6.3. Creating advanced dialogs and windows

With itom it is not only possible to add menus and toolbar elements to the main GUI of itom or to use the default set of input and message boxes, but it is also possible to create own user interfaces. These interfaces are designed by help of a WYSIWYG (“what you see is what you get”) design tool (Qt Designer). The logic behind the surfaces is then scripted using Python. Therefore it is possible to change the appearance of control elements at runtime or to connect a signal, emitted when for instance clicking on a button, with a user-defined python method.

In this chapter, the creation of such user interfaces is explained.

6.3.1. Qt Designer

The Qt Designer can be used to create a GUI for interaction with the itom software.
For details see the Qt Designer documentation under http://doc.qt.io/qt-5/qtdesigner-manual.html

In order to start the Qt Designer, click on the corresponding icon in the toolbar of itom:

../_images/mainsymbols2.png

or double-click on a corresponding ui-file in the file system widget of itom. In the first case, Qt Designer shows an initialization dialog, where you can choose the base type of the user interface you want to create.

../_images/designerNew.png

Note

There is a known issue in the setup 1.4.0 (or earlier) concerning an unsuccessful startup of the external Qt designer. If you want to open the designer using the button in the toolbox of the itom main window, the startup may fail. This bug is known and will be fixed in future releases. Until then, please open the designer either by starting the designer.exe in the application folder of itom or open an existing ui-file (e.g. in the demo folder of itom). This issue only affects setup versions (32bit and 64bit) for Windows.

In principle you have the possibility to choose between three different base layouts:

1. Dialog. A Dialog is usually displayed on top of the main window and only has got one close-button in its title bar. Often, dialogs are used for configuration dialogs where the user finally closes the dialog using one of the standard buttons (OK, Cancel, Apply...) in order to confirm or reject the current changes in the dialog. A dialog cannot have its own toolbar, menu or status bar. 2. Main Window. A main window is a fully equipped main window, which can be minimized, maximized, can have toolbars, menus and a status bar. Therefore it is recommended to use this type of user interface for the main window of your measurement system. Like a dialog, it is possible to show the main window on top of itom (as sub-window of itom) or as independent window, which has its own icon in the windows tray. 3. Widget. A widget is the base class for all control elements provided by Qt. Therefore a widget does not have any title bar or windows frame. Nevertheless you can choose a widget for your user interface, since itom provides the possibility to stack this widget into a default dialog which can optionally show some default buttons on the right side or at the bottom of the dialog. This is the easiest way the generate a configuration dialog in itom, since you do not need to script the necessary methods handling clicks on one of these buttons. In this case, itom automatically gets full information about the close status and type of closing of the dialog (accepted, rejected...).

After having chosen one of these base layouts (types), your surface is displayed in the middle of the Qt Designer and you can start to drag elements from the widget library on your surface. If the Qt Designer is started from itom you will even find a section ITOM Plugins in the library list, which contains all loadable designer plugins that are provided by itom and can also be placed on your surface. The choice of these plugins depend on the designer plugins that are currently available in your installation of itom.

../_images/qtdesigner1.png

After having placed one widget on the canvas, you will see its properties in the property toolbox of Qt Designer. Every widget has the common property objectName. If you assign a unique object name to any of your control elements, it is possible to access and manipulate this widget from a Python script in itom using this name, too. In general many of the properties that are visible in the property toolbox can afterwards be read or changed by an appropriate script (depending on the data type of the property).

The alignment of control elements on the surface is mainly controlled by so-called layout elements. These layouts together with size policies that can be assigned to every widget control the appearance of the entire user interface and provide the feature that the dialog can be changed in size whereas all widgets are dynamically repositioned. For more information about layouting your user interface, see http://qt-project.org/doc/qt-4.8/designer-layouts.html.

Finally, save your user interface under a convenient filename with the suffix .ui.

6.3.1.1. Widget Library

In principle, you are allowed to place every widget on your user interface that is available in the widget library (widget box) of Qt Designer. Later, you will learn how you can access properties of any widget (read and/or write) and how you can call specific functions provided by any widget. However, you will also learn that you do not have access using Python to all functions a widget has and you are not able to sub-class any widget, like you can it using a native C++ program. Therefore, it is not recommended to place any widget from the group Item Views (Model-based) on your user interface since only few functions of these widgets are accessible by a Python script. If you need a list box, use the item-based list widget. itom also provides some widgets (section ITOM widgets) that can be placed on your user interfaces, for instance some plot widgets or the widget for plotting the result of the python module matplotlib (see Python-Module matplotlib).

6.3.2. Loading user interface in itom

In this section, an introduction is given how to create and load user interfaces in itom depending on different type-attributes.

6.3.2.1. Widget embedded in itom-dialog (TYPEDIALOG)

Like described above, the easiest and most comfortable way to load user interfaces in itom is to use the type TYPEDIALOG. In Qt Creator you design a widget with your individual content and then when loading this GUI in itom, the widget is embedded in a dialog provided by itom, which optionally adds a horizontal or vertical button bar at the right side or at the bottom of the dialog.

Let us create an exemplary user interface. In Qt Creator the following widget has been created:

../_images/testWidget.png

On the right side of the widget testWidget you see the hierarchical organization of objects that are put on the widget. At first, a group box has been placed on the widget. Inside of this group box two radio buttons have been placed using a simple drag&drop from the widget library. Both radio buttons are aligned inside of the group box with a vertical layout. This is reached by a right-click on the group box and choosing vertical layout from the layout menu. Below the group box, a widget of type lineedit and a push button (type pushbutton) have been placed. Finally the three main elements are also aligned in a vertical layout with respect to the overall widget. This can be achieved by a right click on an empty space of the widget or directly in the object inspector. If you increase now the size of the overall widget, you will see that all sub-elements are resized according to their layout. Since we don’t want sub-widgets to be vertically stretched and distributed, a vertical spacer element has been placed at the bottom of the vertical layout stack.

The following properties have been directly set in Qt Creator:

  • group box: objectName: groupOption, title: ‘Please make your choice’
  • push button: objectName: btnClickMe, text: ‘click me’
  • line edit: objectName: txtInput, text: ‘put here your text...’
  • radio buttons: objectName: radioOpt1 and radioOpt2, text: ‘Option 1’ and ‘Option 2’

The entire widget is saved under the filename testWidget.ui in an arbitrary directory.

Then you can load and show the widget in itom by creating a python-script in the same directory with the following content. You can also directly type these lines into the command line of itom, however, you should then assure that the current directory is equal to the directory where the user interface has been stored.

dialog = ui("testWidget.ui", ui.TYPEDIALOG) #loading dialog
result = dialog.show(1) #modally show, wait until the dialog has been closed
print("The dialog has been closed with code", result)

At first, an instance of class itom.ui is created that is given the name of the user interface file. This instance can then be accessed by the name dialog. By calling the method show(), the dialog is shown. Since the parameter has been set to 1, the dialog is shown in a modal style, such that python waits until the dialog has been closed again and itom is entirely blocked during that time. However, then it is possible to get informed about the way the dialog is closed, such that the variable result will be set to 0 if the user closed the dialog using a cancel button (not available here) or the close button in the title bar or 1 if the user clicked an OK-button.

../_images/testWidgetItom.png

It is also possible to open the dialog in a non-modal version or to open it in a modal style however to immediately force python to continue the script execution. This depends on the parameters of show(). However only in the modal case above, the closing result can be tracked by Python. Additionally, this is also only possible if a widget is embedded in a dialog, given by itom, like it is always the case if you create an instance of itom.ui with the second parameter set to ui.TYPEDIALOG.

Right now, you don’t have the possibility to quit the dialog using any button (OK, Cancel...). In order to obtain a button bar with these buttons, the call to the class itom.ui needs to be changed. There is the choice between two different appearances of a button bar, which can be automatically added to your widget:

../_images/testWidgetButtonBar.png

Next, you need to select which buttons should be included in the button bar. This is done by creating a python dictionary, where each elements corresponds to one button. The key-word of the item corresponds to the role of the button (see enumeration QDialogButtonBox::ButtonRole* of the Qt-library documentation) and the value is the text of the button. Common roles are:

  • “AcceptRole”: Use this role for an OK-button. The dialog is closed and the return value in modal style is 1.
  • “RejectRole”: Use this role for a Cancel-button. The dialog is also closed but the return value is 0.

Finally, the call to itom.ui must be in the following way, in order to get an auto-generated button bar:

dialog = ui("testWidget.ui", ui.TYPEDIALOG, ui.BUTTONBAR_VERTICAL, \
    {"AcceptRole":"OK", "RejectRole":"Cancel"})
#or
dialog = ui("testWidget.ui", ui.TYPEDIALOG, ui.BUTTONBAR_HORIZONTAL, \
    {"AcceptRole":"Yes", "RejectRole":"No"})

Note

You can also use a keyword-based call to ui since every parameter has its default value such that you can omit parameters beside the first one. For more details about all parameters, keywords and its default values see itom.ui.

The dialog is closed and deleted if the variable dialog is deleted using the command del.

6.3.2.2. Main window or dialog (TYPEWINDOW)

If you are not interested in the exact return value of the dialog but you want to have full control and all available functionalities of any dialog or main window, create an user interface based on a dialog or main window in Qt Designer.

../_images/testWindow.png

The figure shows an exemplary user interface (testWindow.ui) that is based on a main window. On the right side, there have been added three buttons, nested in a vertical layout. On the left side, there is a list widget (objectName: listWidget, type: List Widget). Additionally a menu has been added that consists of three items.

This main window can now be shown using the following code snippet:

win = ui("testWindow.ui", ui.TYPEWINDOW)
win.show() #this is equal to win.show(0) -> non-modal

Then, the window is shown on top of the main window of itom, since it is considered to be a child of itom. If you don’t want this, you can also add the keyword-parameter childOfMainWindow=False to the call of itom.ui:

win = ui("testWindow.ui", ui.TYPEWINDOW, childOfMainWindow=False)

Here, you need to use the keyword, since the parameters dialogButtonBar and dialogButtons (used for TYPEDIALOG) are not given in this case, since they are useless in case of TYPEWINDOW. If your window is no child of itom, it gets its own icon in the Windows tray bar and does not stay on top of itom.

6.3.2.3. Main window or widget as dockable toolbox (TYPEDOCKWIDGET)

It is also possible to integrate user-defined main windows or widgets as dockable toolbox in the main window of itom. This is done using the type value ui.TYPEDOCKWIDGET. Then the widget is registered as dockwidget in the main window of itom and once it becomes visible, its startup position is at the top-center position. You can define the initial dock area using the optional argument dockWidgetArea of the class itom.ui.

win = ui("testWindow.ui", ui.TYPEDOCKWIDGET, dockWidgetArea = ui.RIGHTDOCKWIDGETAREA)

Possible values for dockWidgetArea are:

ui.LEFTDOCKWIDGETAREA = 1 ui.RIGHTDOCKWIDGETAREA = 2 ui.TOPDOCKWIDGETAREA = 4 ui.BOTTOMDOCKWIDGETAREA = 8

6.3.3. Accessing control elements

Until now, you know how to design an interface and how to show it using itom. This and the following sections explain how you dynamically interact with the user interface and its elements. One elementary tool for this is to access any desired element of the GUI. For instance, if you want to change properties of a button or the text of a lineedit-widget, you first need to access these elements.

The accessing is simply done by the unique and specific objectName of each element and the dot-operator (.). Let’s take the first example testWidget.ui again. The dialog has been assigned the variable dialog. Then have the following possibilities to access its elements:

elemGroup = dialog.groupOption # access the group box by its objectName

elemRadioOpt1 = dialog.radioOpt1 # OR
elemRadioOpt1 = elemGroup.radioOpt1

textfield = dialog.txtInput

Each variable created by the code block above is an instance of itom.uiItem. It is this class that defines the dot-operator. Looking at the example of accessing the first radio button, which is a child of the group-box, it is both possible to access the group button by its objectName as child of the entire dialog or as child of the groupbox. This is feasible since the class ui is derived from uiItem, such that the dot-operator not only works for entire dialog references but also for accessing sub-elements of other widgets. However, since each objectName is unique among all elements of the entire dialog, is doesn’t matter how to access any element.

But why do we need to access these elements? Why do they returns its own instance of class uiItem. These questions are answered in the following sections...

6.3.4. Getting and setting properties

As already mentioned, you can read or write most properties of any element that are also listed in the property toolbox of Qt Designer. Properties are also separately listed in the corresponding Qt documentation. In general it makes sense to set properties - when offline possible - in the Qt Designer. This is a little bit more efficient and keeps your script tiny. Getting and setting properties is possible if you have an object of type uiItem. Therefore you need to get this object like described in the section above.

Getting the property value can either be done by using the mapping-operator [] or by using the method getProperty(). For instance, if you want to get the current text and the enabled status of the textfield in dialog testWidget.ui from the first example, you can use one of the following possibilities:

#1. possibility
text = dialog.txtInput["text"]
enabled = dialog.txtInput["enabled"]

#2. possibility
[text,enabled] = dialog.txtInput.getProperty(["text", "enabled"])

In order to set one or multiple properties, you can use similar methods. Simply assign a value to the mapping-operator [] or use the method setProperty().

#1. possibility
dialog.txtInput["text"] = "new text for this textfield"
dialog.txtInput["enabled"] = False

#2. possibility
dialog.txtInput.setProperty( {"text":"new text for this textfield", \
    "enabled":False} )

If you use setProperty(), you always need to pass a dictionary as argument. This dictionary can contain one or multiple properties, where the keyword always is the property-name (string) and the value is the corresponding new value (type depends on corresponding C++ type). For more information about supported datatypes, that can be accessed by python in itom see Supported datatypes.

If the property is an enumeration or a bitmask (or-combination of enumeration values), you can either pass the integer value or a string with the enumeration key name. In case of a flag, pass a semicolon-separated string with all values. The return value is always the integer number.

6.3.5. Supported datatypes

The classes itom.ui and itom.uiItem are the connection between any python-script in itom and GUI-elements, written in C++ and provided by Qt. Therefore, it is necessary to transform types from python to corresponding C++-structures and vice-versa. The following table lists some convenient type casts. In general, it is always tried to convert the input type to the desired destination type, such that a number can also be transformed to a string, if it is always known, that the destination requires a string.

C++/Qt-Type Python-Type
QString str or any type, that has a string representation
QByteArray unicode or byte type
QUrl any string that can be interpreted as Url
bool any type that can be casted to a boolean value (1,0,True,False...)
QStringList any sequence that only contains values castable to QString
int, short, long integer, floats are rounded to integer, True=1, False=0
unsigned int ... integer, floats are rounded to integer, True=1, False=0
float, double integer, floats, True=1.0, False=0.0
QVector<int> any sequence whose values are castable to int
QVector<double> any sequence whose values are castable to double
QVector2D any sequence with two values castable to double (x,y)
QVector3D any sequence with three values castable to double (x,y,z)
QVector4D any sequence with four values castable to double (x,y,z,w)
PCLPointCloud pointCloud
PCLPoint point
PCLPolygonMesh polygonMesh
DataObject* dataObject or any type convertable to an array (see numpy)
AddInDataIO* dataIO
AddInActuator* actuator
QVariant any of the types above can be transformed to QVariant
QVariantMap a dictionary where keys are strings and values are generally convertable.
QVariantList any sequence whose items can be convertable.
QRegion region
QColor string with color name or hex-value or rgba
Enumeration integer with value or string with key (setter only)
QTime datetime.time object
QDate datetime.date object
QDateTime datetime.datetime object
QFont font

If a property or other arguments in Qt require other datatypes, it is possibly to implement a converter for them. It only becomes a little bit more difficult for pointers to extended C++ or Qt classes. The conversion is mainly done in the itom class PythonQtConversion.

6.3.6. Connecting signals

Now, you know how to change properties of dialogs at runtime of itom using a small python script snippet. In this section, you will learn how you can let itom a specific python-method for instance if a button on the user interface is clicked. Whenever something is changed in a user interface or the user starts to interact with the interface, any type of event is emitted. In Qt many of these events are specially handled and called signals. For instance, if an user clicks a button, toggles a checkbox, triggers an item in a menu or selects an item in a list widget, a signal is emitted or sent.

The counterpart to a signal is called slot. Qt provides the possibility to connect a signal with a slot, under the only condition, that both have exactly the same order and type of arguments. It is even possible to connect the same signal to various slots. Whenever a signal is emitted, all connected slots are executed. itom provides you the possibility to define slots in form of ordinary python methods or functions and to also connect them to signals of widgets on your user interface.

For establishing the connection, you need again a reference to the specific widget on the user interface. This reference is any variable of type uiItem. Next, you need the name and the arguments of the Qt signal, you want to connec to. This information can be obtained by the Qt documentation. For instance, if you need any signal that a widget of type QPushButton (the type of our push button, placed in the user interface in file testWidget.ui), go to http://qt-project.org/doc/qt-4.8/qpushbutton.html. Unfortunately, you won’t find a headline called Signals at this page, since QPushButton does not directly declare any signal. However, you can see under Additional Inherited Members, that QPushButton inherits signals from its base classes. The most important signals are inherited from QAbstractButton. Click on its link and you will see the available signals for a push button:

void clicked ( bool checked = false )
void pressed ()
void released ()
void toggled ( bool checked )

If any argument provides a default value, you can also omit the specific argument. Select the signal that is convenient for you and create its string-signature. The signature always contains the following structure:

signature = "signalName(typeName1,typeName2,...)"

For instance, the signatures for the signals above are:

"clicked()" or "clicked(bool)"
"pressed()"
"released()"
"toggled(bool)"

Then, create a python method in your script, which you want to consider to be a slot and that should be connected with the signal. This method always requires the same number of arguments than given in the signature. If you want to connect a signal to a method that is a bounded method of a class in python, the first argument self does not count to the number of total arguments, hence, you always need to define the first parameter self, like it is the case for bounded methods.

Finally, use the method connect() in order to establish the connection. For instance let us create a method, that should show a message when the push button “click me” on the first exemplary dialog (testWidget.ui) has been clicked:

dialog = ui("testWidget.ui", ui.TYPEDIALOG, ui.BUTTONBAR_VERTICAL, \
    {"AcceptRole":"OK", "RejectRole":"Cancel"})

def showMsg():
    #slot executed in button 'click me' is clicked
    ui.msgInformation("itom","you pressed the button click me")

#connect(signature, method)
dialog.btnClickMe.connect( "clicked()", showMsg )

#show dialog
dialog.show()

You have seen that the method connect() of the element dialog.btnClickMe (the push button) has been called. Its first argument is the signature of the signal, as second argument the reference to the slot-methods is given. If you integrate the dialog within a class and the slot is a member of this class, too, the exemplary code can look as follows:

class MyDialog():

    def __init__(self):
        self.dialog = ui("testWidget.ui", ui.TYPEDIALOG, ui.BUTTONBAR_VERTICAL, \
            {"AcceptRole":"OK", "RejectRole":"Cancel"})
        self.dialog.btnClickMe.connect("clicked()", self.showMsg)
        self.dialog.show()

    def showMsg(self):
        ui.msgInformation("itom","you pressed the button click me")

#instance of class MyDialog
test = MyDialog()

Let us use the second example testWindow.ui. If you want a python method to be executed if the user clicks an action in the menu of the main window, you should connect the signal triggered() of every item in the menu with your method. In Qt such an item is an instance of QAction and is also accessed by its objectName.

win = ui("testWindow.ui", ui.TYPEWINDOW)

def addItem():
    print("action addItem clicked")

win.actionAddItem.connect("triggered()", addItem)
#actionAddItem is the objectName of the action
win.show()

6.3.7. Calling slots

Widgets on user interfaces not only emit signals but they also have slots defined, such that you can connect other signals (e.g. from other widgets) to these slots. Using a python script in itom you can also call (or: invoke) these slots.

In order to invoke a slot, call the method call() of any element on your user interface. For instance, in order to clear the list widget (objectName: listWidget) of uiWindow.ui, you can invoke its public slot clear():

win = ui("testWindow.ui", ui.TYPEWINDOW)
listWidget = win.listWidget
listWidget.call("clear")

Here, the method call() is only called with one argument, the name of the slot in Qt. If this slot would have any arguments that can be converted from Python (see Supported datatypes), add these arguments as further parameters to the call.

Unfortunately, there are some methods of important widgets in Qt, which are not defined to be a public slot. For instance, the methods to add item(s) to a list widget are no slots. However, there are some exceptions defined in itom such that some public methods of widgets can also be called with the method call(). These exceptions are contained in the following table:

Widget / ClassName Public Method
QWidget void resize(int,int)
QWidget void setGeometry(int,int,int,int)
QListWidget void addItem(QString)
QListWidget void addItems(QStringList)
QListWidget void selectedRows() returns a tuple of all selected row indices
QListWidget void selectedTexts() returns a tuple of all selected values (as strings)
QListWidget void selectRows(QVector<int>) select the rows with the given indices (ListWidget must be in multi-selection mode)
QComboBox void addItem(QString)
QComboBox void addItems(QStringList)
QComboBox void removeItem(int)
QComboBox void setItemData(int,QVariant) sets the value of the Qt::DisplayRole (displayed text) of the item with the indicated index
QComboBox void insertItem(int,QString)
QComboBox QString itemText(int) returns the text of the i-th item in the combo-box as string
QTabWidget int isTabEnabled(int)
QTabWidget void setTabEnabled(int,bool)
QMainWindow uiItem statusBar() returns a reference to the statusbar widget
QMainWindow uiItem centralWidget() returns a reference to the central widget of the mainWindow
QTableWidget void setHorizontalHeaderLabels(QStringList)
QTableWidget void setVerticalHeaderLabels(QStringList)
QTableWidget QVariant getItem(int,int)
QTableWidget void setItem(int,int,QVariant)
QTableWidget int currentColumn() returns index of selected column
QTableWidget int currentRow() returns index of selected row
QTableView uiItem horizontalHeader()
QTableView uiItem verticalHeader()

Please notice, that every method listed above is also valid for a widget, that is derived from the specific class (derived in C++). Therefore the additional slots of QWidget hold for every other widget, since every widget is derived from QWidget.

6.3.8. Connecting internal signals and slots in Qt Designer

If you want to connect the signal, emitted by any widget, with a slot from another widget, you will learn in this section how to do this. This type of connection can for instance be useful if you want to enable or disable certain widgets depending on the status of other ones, like the check-status of a checkbox. The following figure shows an user interface with a checkbox and a textfield. Let us define a signal-slot-connection, such that the textfield gets disabled if the checkbox is unchecked.

../_images/uiSignalSlot1.png

This type of gui-internal connections are completely done in Qt Creator. Therefore chose the “Signal and Slots” editing mode, that is obtained by clicking the symbol qtsignalslotmode in the toolbar or by pressing F4. Then you can make a drag&drop connection between the emitting widget and the receiver-widget. After releasing the mouse button, the connection dialog, depicted in the following figure becomes visible:

../_images/uiSignalSlot2.png

Here you can choose which signal of the emitting widget should be connected with which slot of the destination. At the beginning, only slots and signals of the specific widget classes are visible. However, you can check the checkbox below, in order to also show the signals and slots of the inherited classes. Please make sure, that you only choose pairs of signals and slots which have the same parameter types. In our case, we connect the signal toggled(bool) with the slot setEnabled(bool), which is the setter-method of the property enabled.

This example has also shown, that not only slots defined in the slot-section can be called as slots, but also every setter-method of any property can be called like every slot. However, in this case it is more convenient the property like described in section Getting and setting properties.

6.3.9. Auto-connecting signals using python decorators

itom provides an optional approach to directly connect methods with a specific signal of a widget. An example for this approach is for instance given in the demo script autoConnectDemo.py in the demo/ui subfolder of the itom installation.

The concept is as follows:

  1. import the class ItomUi from the module itomUi (located in the subfolder itom_packages that is part of the Python search path:

    from itomUi import ItomUi
    
  2. Create a class that is derived from ItomUi

  3. In the constructor (method __init__) of your class call the constructor of the base class ItomUi. This constructor has the same arguments than the class itom.ui. This is where you create the GUI from the ui file.

  4. The ui is accessible via the member variable gui of your class, hence, within a member method write self.gui to access the user interface and its widgets.

  5. You can now connect one or multiple signals from one widget to one member method of your class.

  6. The name of the member method must be:

    def on_ObjectNameOfWidget_SignalName(self, [arg1, arg2, ...]):
        pass
    
  7. The argument is self (like it is always the case in object-oriented Python programming) followed by a series of arguments. The number of these arguments must correspond to the number of arguments the signal has.

  8. Write one or multiple decorators above the method signature, to establish the connection. The decorator looks like this:

    @ItomUi.autoslot("args")
    
    Hereby, *args* corresponds to a comma separated list of all type names (in C++) the Qt signal is emitting.
    

As an example, we want to connect the valueChanged signal of a spin box (object-name: spinTestBox, argument obtained from Qt help: one int):

@ItomUi.autoslot("int")
def on_spinTestBox_valueChanged(self, value):
    print("The value of the spin box changed to", value)

6.3.10. Debugging user interfaces and slot-methods

If you established a signal-slot-connection between an element of the GUI and a Python-method, you probably want to debug this method once the signal has been emitted. This is obtained by setting any breakpoint into the specific line and toggling the button Run python code in debug mode in the menu Script of itom.

../_images/runPyCodeInDebug.png

6.3.11. Access the status bar of a main window

If one wants to access and modify the content of the status bar of a main window, the following steps need to be done:

Let’s assume the main window is accessible via Python by the variable name gui, then

statusbar = gui.call("statusBar")

returns an instance of uiItem representing the status bar widget (Qt class QStatusBar). Check the Qt help to see that QStatusBar has the following slots (among others):

  • clearMessage() clears the current text of the status bar
  • showMessage(const QString &message) displays message in the status bar
  • showMessage(const QString &message, int timeout) displays message in the status bar and hides it after the timeout given in milliseconds.

6.3.12. Hints and limitations

All methods described in this chapter explain how to create and use user-defined dialogs and windows using Python scripts in itom. Finally, all dialogs are created using the Qt-framework. The classes itom.ui and itom.uiItem finally are wrappers for the underlying Qt-system. Using pure python, similar things can also be obtained with the famous packages PyQt or PySide. However, in itom you must not use these packages. The reason is, that create a new main instance of the Qt-engine, that needs to be created in the main thread. This is the case, if PyQt or PySide is executed directly in Python. However using itom Python is embedded as scripting language, such that itom is executed in the main thread while Python is moved to its own additional thread. The reason is to enable the execution of longer scripts, while the main application itom still keeps reactive. Therefore, Python does not have access to the real main thread and it is forbidden to explicitly execute some GUI-related stuff in secondary threads. Therefore all methods in itom.ui and itom.uiItem have thread-safe implementations and communicate with an organization structure, that runs in the main thread of itom, in order to interact with all dialogs.