QScriptContext Class

The QScriptContext class represents a Qt Script function invocation. 更多...

头: #include <QScriptContext>
qmake: QT += script
Since: Qt 4.3

该类在 Qt 4.3 引入。

公共类型

enum Error { ReferenceError, SyntaxError, TypeError, RangeError, URIError, UnknownError }
enum ExecutionState { NormalState, ExceptionState }

公共函数

~QScriptContext ()
QScriptValue activationObject () const
QScriptValue argument (int index ) const
int argumentCount () const
QScriptValue argumentsObject () const
QStringList backtrace () const
QScriptValue callee () const
QScriptEngine * engine () const
bool isCalledAsConstructor () const
QScriptContext * parentContext () const
void setActivationObject (const QScriptValue & activation )
void setThisObject (const QScriptValue & thisObject )
QScriptContext::ExecutionState state () const
QScriptValue thisObject () const
QScriptValue throwError (QScriptContext::Error error , const QString & text )
QScriptValue throwError (const QString & text )
QScriptValue throwValue (const QScriptValue & value )
QString toString () const

详细描述

A QScriptContext provides access to the `this' object and arguments passed to a script function. You typically want to access this information when you're writing a native (C++) function (see QScriptEngine::newFunction ()) that will be called from script code. For example, when the script code

foo(20.5, "hello", new Object())
					

is evaluated, a QScriptContext will be created, and the context will carry the arguments as QScriptValues; in this particular case, the arguments will be one QScriptValue containing the number 20.5, a second QScriptValue containing the string "hello" , and a third QScriptValue containing a Qt Script object.

使用 argumentCount () to get the number of arguments passed to the function, and argument () to get an argument at a certain index. The argumentsObject () function returns a Qt Script array object containing all the arguments; you can use the QScriptValueIterator to iterate over its elements, or pass the array on as arguments to another script function using QScriptValue::call ().

使用 thisObject () to get the `this' object associated with the function call, and setThisObject () to set the `this' object. If you are implementing a native "instance method", you typically fetch the thisObject () and access one or more of its properties:

QScriptValue Person_prototype_fullName(QScriptContext *context, QScriptEngine *engine)
{
    QScriptValue self = context->thisObject();
    QString result;
    result += self.property("firstName").toString();
    result += QLatin1String(" ");
    result += self.property("lastName").toString();
    return result;
}
					

使用 isCalledAsConstructor () to determine if the function was called as a constructor (e.g. "new foo()" (as constructor) or just "foo()" ). When a function is called as a constructor, the thisObject () contains the newly constructed object that the function is expected to initialize.

使用 throwValue () 或 throwError () to throw an exception.

使用 callee () to obtain the QScriptValue that represents the function being called. This can for example be used to call the function recursively.

使用 parentContext () to get a pointer to the context that precedes this context in the activation stack. This is mostly useful for debugging purposes (e.g. when constructing some form of backtrace).

The activationObject () function returns the object that is used to hold the local variables associated with this function call. You can replace the activation object by calling setActivationObject (). A typical usage of these functions is when you want script code to be evaluated in the context of the parent context, e.g. to implement an include() function:

QScriptValue myInclude(QScriptContext *ctx, QScriptEngine *eng)
{
    QString fileName = ctx->argument(0).toString();
    QString contents = readTheFile(fileName);
    ctx->setActivationObject(ctx->parentContext()->activationObject());
    ctx->setThisObject(ctx->parentContext()->thisObject());
    return eng->evaluate(contents, fileName);
}
					

使用 backtrace () to get a human-readable backtrace associated with this context. This can be useful for debugging purposes when implementing native functions. The toString () function provides a string representation of the context. ( QScriptContextInfo provides more detailed debugging-related information about the QScriptContext.)

使用 engine () to obtain a pointer to the QScriptEngine that this context resides in.

另请参阅 QScriptContextInfo , QScriptEngine::newFunction (),和 QScriptable .

成员类型文档编制

enum QScriptContext:: Error

This enum specifies types of error.

常量 描述
QScriptContext::ReferenceError 1 A reference error.
QScriptContext::SyntaxError 2 A syntax error.
QScriptContext::TypeError 3 A type error.
QScriptContext::RangeError 4 A range error.
QScriptContext::URIError 5 A URI error.
QScriptContext::UnknownError 0 An unknown error.

enum QScriptContext:: ExecutionState

This enum specifies the frameution state of the context.

常量 描述
QScriptContext::NormalState 0 The context is in a normal state.
QScriptContext::ExceptionState 1 The context is in an exceptional state.

成员函数文档编制

QScriptContext:: ~QScriptContext ()

销毁此 QScriptContext .

QScriptValue QScriptContext:: activationObject () const

Returns the activation object of this QScriptContext . The activation object provides access to the local variables associated with this context.

注意: The activation object might not be available if there is no active QScriptEngineAgent , as it might be optimized.

另请参阅 setActivationObject (), argument (),和 argumentsObject ().

QScriptValue QScriptContext:: argument ( int index ) const

Returns the function argument at the given index .

index >= argumentCount (), QScriptValue of the primitive type Undefined is returned.

另请参阅 argumentCount ().

int QScriptContext:: argumentCount () const

Returns the number of arguments passed to the function in this invocation.

Note that the argument count can be different from the formal number of arguments (the length property of callee ()).

另请参阅 argument ().

QScriptValue QScriptContext:: argumentsObject () const

Returns the arguments object of this QScriptContext .

The arguments object has properties callee (equal to callee ()) and length (equal to argumentCount ()), and properties 0 , 1 , ..., argumentCount () - 1 that provide access to the argument values. Initially, property P (0 <= P < argumentCount ()) has the same value as argument( P ). In the case when P is less than the number of formal parameters of the function, P shares its value with the corresponding property of the activation object ( activationObject ()). This means that changing this property changes the corresponding property of the activation object and vice versa.

另请参阅 argument () 和 activationObject ().

QStringList QScriptContext:: backtrace () const

Returns a human-readable backtrace of this QScriptContext .

Each line is of the form <function-name>(<arguments>)@<file-name>:<line-number> .

To access individual pieces of debugging-related information (for example, to construct your own backtrace representation), use QScriptContextInfo .

另请参阅 QScriptEngine::uncaughtExceptionBacktrace (), QScriptContextInfo ,和 toString ().

QScriptValue QScriptContext:: callee () const

Returns the callee. The callee is the function object that this QScriptContext represents an invocation of.

QScriptEngine *QScriptContext:: engine () const

返回 QScriptEngine that this QScriptContext belongs to.

bool QScriptContext:: isCalledAsConstructor () const

Returns true if the function was called as a constructor (e.g. "new foo()" ); otherwise returns false.

When a function is called as constructor, the thisObject () contains the newly constructed object to be initialized.

注意: This function is only guaranteed to work for a context corresponding to native functions.

QScriptContext *QScriptContext:: parentContext () const

Returns the parent context of this QScriptContext .

void QScriptContext:: setActivationObject (const QScriptValue & activation )

Sets the activation object of this QScriptContext to be the given activation .

activation is not an object, this function does nothing.

注意: For a context corresponding to a JavaScript function, this is only guaranteed to work if there was an QScriptEngineAgent active on the engine while the function was evaluated.

另请参阅 activationObject ().

void QScriptContext:: setThisObject (const QScriptValue & thisObject )

Sets the `this' object associated with this QScriptContext thisObject .

thisObject is not an object, this function does nothing.

另请参阅 thisObject ().

QScriptContext::ExecutionState QScriptContext:: state () const

Returns the frameution state of this QScriptContext .

QScriptValue QScriptContext:: thisObject () const

Returns the `this' object associated with this QScriptContext .

另请参阅 setThisObject ().

QScriptValue QScriptContext:: throwError ( QScriptContext::Error error , const QString & text )

Throws an error 采用给定 text . Returns the created error object.

The text will be stored in the message property of the error object.

The error object will be initialized to contain information about the location where the error occurred; specifically, it will have properties lineNumber , fileName and stack . These properties are described in Qt Script Extensions to ECMAScript .

另请参阅 throwValue () 和 state ().

QScriptValue QScriptContext:: throwError (const QString & text )

这是重载函数。

Throws an error with the given text . Returns the created error object.

另请参阅 throwValue () 和 state ().

QScriptValue QScriptContext:: throwValue (const QScriptValue & value )

Throws an exception with the given value . Returns the value thrown (the same as the argument).

另请参阅 throwError () 和 state ().

QString QScriptContext:: toString () const

Returns a string representation of this context. This is useful for debugging.

该函数在 Qt 4.4 引入。

另请参阅 backtrace ().