QQmlExpression ¶

概要 ¶

详细描述 ¶

For example, given a file main.qml 像这样：

The following code evaluates a JavaScript expression in the context of the above QML:

QQmlEngine *engine = new QQmlEngine;
QQmlComponent component(engine, QUrl::fromLocalFile("main.qml"));
QObject *myObject = component.create();
QQmlExpression *expr = new QQmlExpression(engine->rootContext(), myObject, "width * 2");
int result = expr->evaluate().toInt();  // result = 400
											

class QQmlExpression ¶

QQmlExpression(arg__1, arg__2, arg__3[, arg__4=None])

QQmlExpression(arg__1[, arg__2=None[, arg__3=None[, arg__4=None]]])

param arg__1

QQmlContext

param arg__2

QObject

param arg__3

unicode

param arg__4

QObject

Create an invalid QQmlExpression .

As the expression will not have an associated QQmlContext , this will be a null expression object and its value will always be an invalid QVariant .

PySide2.QtQml.QQmlExpression. clearError ( ) ¶

Clear any expression errors. Calls to hasError() following this will return false.

另请参阅

hasError() error()

PySide2.QtQml.QQmlExpression. columnNumber ( ) ¶

返回类型

int

Returns the source file column number for this expression. The source location must have been previously set by calling setSourceLocation() .

PySide2.QtQml.QQmlExpression. context ( ) ¶

返回类型

QQmlContext

返回 QQmlContext this expression is associated with, or 0 if there is no association or the QQmlContext has been destroyed.

PySide2.QtQml.QQmlExpression. engine ( ) ¶

返回类型

QQmlEngine

返回 QQmlEngine this expression is associated with, or 0 if there is no association or the QQmlEngine has been destroyed.

PySide2.QtQml.QQmlExpression. error ( ) ¶

返回类型

QQmlError

Return any error from the last call to evaluate() . If there was no error, this returns an invalid QQmlError 实例。

另请参阅

hasError() clearError()

PySide2.QtQml.QQmlExpression. evaluate ( ) ¶

返回类型

PyTuple

Evaulates the expression, returning the result of the evaluation, or an invalid QVariant if the expression is invalid or has an error.

valueIsUndefined is set to true if the expression resulted in an undefined value.

另请参阅

hasError() error()

PySide2.QtQml.QQmlExpression. expression ( ) ¶

返回类型

unicode

Returns the expression string.

另请参阅

setExpression()

PySide2.QtQml.QQmlExpression. hasError ( ) ¶

返回类型

bool

Returns true if the last call to evaluate() resulted in an error, otherwise false.

另请参阅

error() clearError()

PySide2.QtQml.QQmlExpression. lineNumber ( ) ¶

返回类型

int

Returns the source file line number for this expression. The source location must have been previously set by calling setSourceLocation() .

PySide2.QtQml.QQmlExpression. notifyOnValueChanged ( ) ¶

返回类型

bool

返回 true 若 valueChanged() signal is emitted when the expression’s evaluated value changes.

另请参阅

setNotifyOnValueChanged()

PySide2.QtQml.QQmlExpression. scopeObject ( ) ¶

返回类型

QObject

Returns the expression’s scope object, if provided, otherwise 0.

In addition to data provided by the expression’s QQmlContext , the scope object’s properties are also in scope during the expression’s evaluation.

PySide2.QtQml.QQmlExpression. setExpression ( arg__1 ) ¶

参数

arg__1 – unicode

Set the expression to expression .

另请参阅

expression()

PySide2.QtQml.QQmlExpression. setNotifyOnValueChanged ( arg__1 ) ¶

参数

arg__1 – bool

Sets whether the valueChanged() signal is emitted when the expression’s evaluated value changes.

若 notifyOnChange is true, the QQmlExpression will monitor properties involved in the expression’s evaluation, and emit valueChanged() if they have changed. This allows an application to ensure that any value associated with the result of the expression remains up to date.

若 notifyOnChange is false (default), the QQmlExpression will not montitor properties involved in the expression’s evaluation, and valueChanged() will never be emitted. This is more efficient if an application wants a “one off” evaluation of the expression.

另请参阅

notifyOnValueChanged()

PySide2.QtQml.QQmlExpression. setSourceLocation ( fileName , line [ , column=0 ] ) ¶

参数

• fileName – unicode

• line – int

• column – int

Set the location of this expression to line and column of url . This information is used by the script engine.

PySide2.QtQml.QQmlExpression. sourceFile ( ) ¶

返回类型

unicode

Returns the source file URL for this expression. The source location must have been previously set by calling setSourceLocation() .

PySide2.QtQml.QQmlExpression. valueChanged ( ) ¶