QGIS Plugin Development – How to Add or Select Layer in QGIS Plugin Like QgsProcessingAlgorithm

Question

I want to have this add from the file or select layer in my plugin widget like:

I think it can be done with some combination of QgsFileWidget and QgsMapLayerComboBox yet one just selects a file path into text input while another only selects existing layers.

So How to add or select a layer in QGIS standalone plugin (inside any QDialog) (like they do it in QgsProcessingAlgorithm)?

Answer 1

Processing algorithm dialogs use widget wrappers for different parameters such as QgsProcessingMapLayerComboBox, which is what you are referring to. I don't know of a similar generic out-of-the-box 'map layer/ file selection combination widget' which you can use in standard, non-processing Python plugins. I may be wrong here, but I think you will have to implement your own solution by writing a basic kind of widget wrapper. I present a simple example below, for vector layers, which should give you an idea of how this would work and how you could use this idea in a plugin.

from pathlib import Path

class InputLayerFileWidget(QWidget):
    def __init__(self, parent=None):
        self.parent = parent
        QWidget.__init__(self)
        self.v_layout = QVBoxLayout()
        self.lbl = QLabel('Input layer:')
        self.selection_widget = QWidget()
        self.h_layout = QHBoxLayout()
        self.mlcb = QgsMapLayerComboBox(self.selection_widget)
        self.mlcb.setFilters(QgsMapLayerProxyModel.VectorLayer)
        self.file_selection_button = QPushButton("\u2026", self.selection_widget)
        self.file_selection_button.setMaximumWidth(30)
        self.file_selection_button.setToolTip('Select from file')
        for c in self.selection_widget.children():
            self.h_layout.addWidget(c)
        self.selection_widget.setLayout(self.h_layout)
        self.v_layout.addWidget(self.lbl)
        self.v_layout.addWidget(self.selection_widget)
        self.setLayout(self.v_layout)
        
        self.file_selection_button.clicked.connect(self.getFile)
        
    def getFile(self):
        file_name = QFileDialog.getOpenFileName(None, 'Select file', '', filter='*.shp; *.gpkg; *.tab')
        if file_name:
            self.mlcb.setAdditionalItems([file_name[0]])
            self.mlcb.setCurrentIndex(self.mlcb.model().rowCount()-1)
                
    def currentLayer(self):
        layer = self.mlcb.currentLayer()
        if layer is not None:
            return layer
        else:
            path = self.mlcb.currentText()
            name = Path(path).stem
            layer = QgsVectorLayer(path, name, 'ogr')
            if layer.isValid():
                return layer
        return None

class MainDialog(QDialog):
    def __init__(self):
        QDialog.__init__(self)
        self.layout = QVBoxLayout()
        self.input_layer_widget = InputLayerFileWidget(self)
        self.lbl = QLabel('Layer object info...', self)
        self.btn = QPushButton('Get Input Layer', self)
        self.layout.addWidget(self.input_layer_widget)
        for _widget in self.children():
            self.layout.addWidget(_widget)
        self.setLayout(self.layout)
        self.setGeometry(200, 200, 1000, 250)
        
        self.btn.clicked.connect(self.get_input_layer)
    
    def get_input_layer(self):
        self.lbl.setText(str(self.input_layer_widget.currentLayer()))
        
        
w = MainDialog()
w.show()

Demonstration screencast of resulting functionality: