Class: QgsExpressionLineEdit

A widget which includes a line edit for entering expressions together with a button to open the expression creation dialog.

This widget is designed for use in contexts where no layer fields are available for use in an expression. In contexts where the expression is directly associated with a layer and fields can be used, then QgsFieldExpressionWidget is a more appropriate choice as it gives users direct access to select fields from a drop-down list.

QgsExpressionLineEdit also supports a multiline editor mode which is useful where more space is available for the widget, but where QgsExpressionBuilderWidget is too complex or large for use.

Class Hierarchy

Base classes

QWidget
QObject
QPaintDevice

Methods

expectedOutputFormat	Returns the expected format string, which is shown in the expression builder dialog for the widget.
expression	Returns the current expression shown in the widget.
expressionDialogTitle	Returns the title used for the expression dialog.
isValidExpression	Determines if the current expression is valid.
registerExpressionContextGenerator	Register an expression context generator class that will be used to retrieve an expression context for the widget.
setExpectedOutputFormat	Set the expected format string, which is shown in the expression builder dialog for the widget.
setExpression	Sets the current expression to show in the widget.
setExpressionDialogTitle	Sets the title used in the expression builder dialog
setGeomCalculator	Set the geometry calculator used in the expression dialog.
setLayer	Sets a layer associated with the widget.
setMultiLine	Sets whether the widget should show a multiline text editor.

Signals

expressionChanged

Emitted when the expression is changed.

class qgis.gui.QgsExpressionLineEdit

Bases: QWidget

__init__(parent: QWidget | None = None)

Constructor for QgsExpressionLineEdit.

Parameters:

parent (Optional[QWidget] = None) – parent widget

expectedOutputFormat(self) → str

Returns the expected format string, which is shown in the expression builder dialog for the widget. This is purely a text format and no expression validation is done against it.

See also

setExpectedOutputFormat()

Added in version 3.4.

Return type:

str

expression(self) → str

Returns the current expression shown in the widget.

See also

setExpression()

Return type:

str

signal expressionChanged(expression: str)

Emitted when the expression is changed.

Parameters:

expression (str) – new expression

expressionDialogTitle(self) → str

Returns the title used for the expression dialog.

See also

setExpressionDialogTitle()

Return type:

str

isValidExpression(self)

Determines if the current expression is valid.

Returns:

• True if the current expression is valid.

• expressionError: any generated error message

registerExpressionContextGenerator(self, generator: QgsExpressionContextGenerator | None)

Register an expression context generator class that will be used to retrieve an expression context for the widget.

Parameters:

generator (Optional[QgsExpressionContextGenerator]) – A QgsExpressionContextGenerator class that will be used to create an expression context when required.

setExpectedOutputFormat(self, expected: str | None)

Set the expected format string, which is shown in the expression builder dialog for the widget. This is purely a text format and no expression validation is done against it.

See also

expectedOutputFormat()

Added in version 3.4.

Parameters:

expected (Optional[str])

setExpression(self, expression: str | None)

Sets the current expression to show in the widget.

Parameters:

expression (Optional[str]) – expression string

See also

expression()

setExpressionDialogTitle(self, title: str | None)

Sets the title used in the expression builder dialog

Parameters:

title (Optional[str]) – dialog title

See also

expressionDialogTitle()

setGeomCalculator(self, distanceArea: QgsDistanceArea)

Set the geometry calculator used in the expression dialog.

Parameters:

distanceArea (QgsDistanceArea) – calculator

setLayer(self, layer: QgsVectorLayer | None)

Sets a layer associated with the widget. Required in order to get the fields and values from the layer. This will also automatically register the layer as expression context generator if no generator has been set before or the previous layer has been used as generator.

See also

registerExpressionContextGenerator()

Parameters:

layer (Optional[QgsVectorLayer])

setMultiLine(self, multiLine: bool)

Sets whether the widget should show a multiline text editor.

Parameters:

multiLine (bool) – set to True to show multiline editor, or False to show single line editor (the default).