The QDeclarativeExpression class evaluates JavaScript in a QML context. 更多...
继承 QObject .
The QDeclarativeExpression class evaluates JavaScript in a QML context.
For example, given a file main.qml 像这样：
import QtQuick 1.0 Item { width: 200; height: 200 }
The following code evaluates a JavaScript expression in the context of the above QML:
QDeclarativeEngine *engine = new QDeclarativeEngine; QDeclarativeComponent component(engine, QUrl.fromLocalFile("main.qml")); QObject *myObject = component.create(); QDeclarativeExpression *expr = new QDeclarativeExpression(engine->rootContext(), myObject, "width * 2"); int result = expr->evaluate().toInt(); // result = 400
Create an invalid QDeclarativeExpression .
As the expression will not have an associated QDeclarativeContext , this will be a null expression object and its value will always be an invalid QVariant .
parent argument, if not None, causes self to be owned by Qt instead of PyQt.
创建 QDeclarativeExpression object that is a child of parent .
expression JavaScript will be executed in the ctxt QDeclarativeContext . If specified, the scope object's properties will also be in scope during the expression's execution.
Clear any expression errors. Calls to hasError () following this will return false.
返回 QDeclarativeContext this expression is associated with, or 0 if there is no association or the QDeclarativeContext has been destroyed.
返回 QDeclarativeEngine this expression is associated with, or 0 if there is no association or the QDeclarativeEngine has been destroyed.
Return any error from the last call to evaluate (). If there was no error, this returns an invalid QDeclarativeError 实例。
另请参阅 hasError () 和 clearError ().
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.
Returns the expression string.
另请参阅 setExpression ().
Returns true if the last call to evaluate () resulted in an error, otherwise false.
另请参阅 error () 和 clearError ().
Returns the source file line number for this expression. The source location must have been previously set by calling setSourceLocation ().
返回 true 若 valueChanged () signal is emitted when the expression's evaluated value 改变。
另请参阅 setNotifyOnValueChanged ().
Returns the expression's scope object, if provided, otherwise 0.
In addition to data provided by the expression's QDeclarativeContext , the scope object's properties are also in scope during the expression's evaluation.
Set the expression to expression .
另请参阅 expression ().
Sets whether the valueChanged () signal is emitted when the expression's evaluated value 改变。
若 notifyOnChange is true, the QDeclarativeExpression will monitor properties involved in the expression's evaluation, and emit QDeclarativeExpression.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 QDeclarativeExpression will not montitor properties involved in the expression's evaluation, and QDeclarativeExpression.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 ().
Set the location of this expression to line of url . This information is used by the script engine.
Returns the source file URL for this expression. The source location must have been previously set by calling setSourceLocation ().
This is the default overload of this signal.
Emitted each time the expression value changes from the last time it was evaluated. The expression must have been evaluated at least once (by calling QDeclarativeExpression.evaluate ()) before this signal will be emitted.
