PyQGIS – Making a Feature Form for Standalone Application

pyqgispyqtqgisstandalone

In QGIS, there is a method named openFeatureForm defined in QgisInterface class. It opens a form that shows value of attributes for a given feature.

layer = iface.activeLayer()
feature = layer.getFeature(0)

iface.openFeatureForm(layer, feature)

This method doesn't work in a standalone PyQGIS application. Because iface is predefined variable that refers QGIS interface.

How can I make a form like that showing the attribute values of a given feature? I also would prefer to filter the attributes.

Best Answer

The following script generates a simple form. You can use it in your standalone PyQGIS application to display attributes for a given feature. You can also specify fields to be displayed (or not to be displayed).


from qgis.PyQt.QtWidgets import *

class FeatureForm(QWidget):
    
    def __init__(self, layer, feature, only=None, exclude=None):                
        super(FeatureForm, self).__init__()
        field_names = layer.fields().names()

        # 'only' parameter is primary. If given, 'exclude' is skipped 
        if only:
            field_names = [f for f in field_names if f in only]
        elif exclude:
            field_names = [f for f in field_names if f not in exclude]
        
        v_layout = QVBoxLayout()
        f_layout = QFormLayout()
        
        for field_name in field_names:
            text_field = QLineEdit()
            text_field.setReadOnly(True)
            text_field.setText(str(feature[field_name]))
            f_layout.addRow(QLabel(field_name), text_field)
        
            self.setLayout(f_layout)

# Sample `layer` and `feature`:
layer = QgsVectorLayer('file_path.shp', "layer_name", "ogr")
feature = layer.getFeature(0)

Without only and exclude:

form = FeatureForm(layer, feature)
form.show()

With only parameter: Just Type and Area are displayed

form = FeatureForm(layer, feature, only=["Type", "Area"])
form.show()

With exclude parameter: All fields are displayed except of Type and Area

form = FeatureForm(layer, feature, exclude=["Type", "Area"])
form.show()

Related Solutions

PyQGIS – Accessing iface API from Standalone Python Script

I'm not the QGIS Standalone application expert, but it seems logical to me that you can't access the iface variable, because it represents the QGIS Dialog, but your are in a standalone application, without the QGIS DIalog by definition.

Side note, in your question, you are referring to QgsMapVectorLayer and QgsMapVectorRegistry which doesn't exist. I guess you are talking about QgsVectorLayer. The QgsMapLayerRegistry has been removed since QGIS 3: https://gis.stackexchange.com/a/244467/24505 If you are still using QGIS 2, I suggest you to update to QGIS 3.4 which the LTR version.

So to add a layer, you can use addMapLayer from QgsProject: https://qgis.org/pyqgis/master/core/QgsProject.html?highlight=project#qgis.core.QgsProject.addMapLayer

Here is a example of a dialog showing a point.

#!/usr/bin/env python3

from qgis.core import (
    QgsApplication, QgsVectorLayer, QgsProject, QgsFeature, QgsGeometry)
from qgis.gui import QgsMapCanvas, QgsLayerTreeMapCanvasBridge
from qgis.PyQt.QtWidgets import QDialog, QVBoxLayout


class MyDialog(QDialog):

    def __init__(self, parent):
        QDialog.__init__(self)
        self.parent = parent
        self.setLayout(QVBoxLayout())

        project = QgsProject()
        canvas = QgsMapCanvas()
        bridge = QgsLayerTreeMapCanvasBridge(
            project.layerTreeRoot(),
            canvas
        )
        bridge.setCanvasLayers()
        self.layout().addWidget(canvas)

        layer = QgsVectorLayer(
            'Point?'
            'crs=epsg:4326&'
            'field=id:integer&field=name:string(20)&index=yes',
            'layer', 'memory')

        feature = QgsFeature()
        feature.setGeometry(QgsGeometry.fromWkt('POINT(10 10)'))
        feature.setAttributes([1, 'Point'])
        layer.startEditing()
        layer.addFeature(feature)
        layer.commitChanges()
        layer.updateExtents()
        project.addMapLayer(layer)
        canvas.zoomToFullExtent()
        self.exec_()


if __name__ == '__main__':
    QgsApplication.setPrefixPath('/application/path/to/adapt', True)
    application = QgsApplication([], True)
    application.initQgis()
    dialog = MyDialog(application)
    application.exitQgis()

The bridge makes the link between your QgsProject and your QgsMapCanvas. So you when you add a layer in project, it displayed in the map canvas.

PyQGIS – Unexpected Behavior in Custom Feature Form with Python Logic

I concur that there seems to be an issue with disconnecting the save() and resetValues() slots from the accepted and rejected signals of the QDialogButtonBox of QgsAttributeForm. Indeed, perusing the docs, I saw that the QgsAttributeForm class has a method disconnectButtonBox() which should take care of this nicely. Inspecting the c++ source code you can see that this method should simply disconnect both those slots from the button box signals. Unfortunately, I was just not able to get it to work.

Below is an effective workaround which makes use of the QgsAttributeForm.hideButtonBox() method which does work. The basic idea is that we add two new, separate QPushButtons to the custom .ui, which we connect to our own slot functions. We also hide the existing button box (which is the workaround for disconnecting the slots from it's signals).

It takes a little more effort to set up the custom .ui file in QtDesigner. Instead of using the 'create dialog with buttons bottom' option, I created a dialog without buttons. I then added the two QPushButton objects (with a horizontal box layout); the rest of the form dialog is much the same. You still need to make sure the line edit object names match your field names. Additionally, I renamed the two push buttons btn_OK and btn_Cancel as we will be accessing them in the Python logic later. To make things look nice, I used a form layout for the whole dialog, set a maximum width for the two push buttons of 75, and added a couple of spacers. My dialog in QtDesigner looks like this:

The object names are:

Segment ID line edit --> Segment_ID

Name line edit --> Name

OK push button --> btn_OK

Cancel push button --> btn_Cancel

The Python file to add the logic looks like this:

from PyQt5.QtCore import *
from PyQt5.QtWidgets import *
 
nameField = None
myDialog = None
 
def formOpen(dialog, layerid, featureid):
    global myDialog
    myDialog = dialog
    global nameField
    nameField = dialog.findChild(QLineEdit,'Name')
    buttonOK = dialog.findChild(QPushButton, 'btn_OK')
    buttonCancel = dialog.findChild(QPushButton, 'btn_Cancel')
    myDialog.hideButtonBox()
    buttonOK.clicked.connect(validate)
    buttonCancel.clicked.connect(close_dialog)
    
def validate():
  # Make sure that the name field isn't empty.
    if not len(nameField.text()) > 0 or nameField.text() == 'NULL':
        msgBox = QMessageBox()
        msgBox.setText('Name field can not be null.')
        msgBox.exec_()
        myDialog.resetValues()
    else:
        # Return the form as accpeted to QGIS.
        myDialog.save()
        close_dialog()
            
def close_dialog():
    if isinstance(myDialog.parent(), QDialog):
        myDialog.parent().close()

After enabling macros in Settings-> Options-> General-> Project Files, I recorded the following two short screencasts showing the resulting behavior when adding and editing features.

Adding a new feature:

Editing an existing feature:

Best Answer

Related Solutions

PyQGIS – Accessing iface API from Standalone Python Script

PyQGIS – Unexpected Behavior in Custom Feature Form with Python Logic

Related Question