Qt 4.3: QScriptContext Class Reference

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# QScriptContext Class Reference
[QtScript module]

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

     #include <QScriptContext>

This class was introduced in Qt 4.3.

- List of all members, including inherited members

### Public Types

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

### Public Functions

- ~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 )
- ExecutionState state () const
- QScriptValue thisObject () const
- QScriptValue throwError ( Error error, const QString & text )
- QScriptValue throwError ( const QString & text )
- QScriptValue throwValue ( const QScriptValue & value )

## Detailed Description

The QScriptContext class represents a Qt Script function invocation.

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.

Use argumentCount() to get the number of arguments passed to the function, and argument() to get an argument at a certain index.

Use thisObject() to get the `this' object associated with the function call, and setThisObject() to set the `this' object.

Use isCalledAsConstructor() to determine if the function was called as a constructor (e.g. `"new foo()"` (as constructor) or just `"foo()"`).

Use throwValue() or throwError() to throw an exception.

Use callee() to obtain the QScriptValue that represents the function being called.

Use parentContext() to get a pointer to the context that precedes this context in the activation stack.

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

Use backtrace() to get a human-readable backtrace associated with this context. This can be useful for debugging purposes when implementing native functions.

See also QScriptEngine::newFunction() and QScriptable.

## Member Type Documentation

### enum QScriptContext::Error

This enum specifies types of error.

Constant | Value | Description
--- | --- | ---
`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 execution state of the context.

Constant | Value | Description
--- | --- | ---
`QScriptContext::NormalState` | `0` | The context is in a normal state.
`QScriptContext::ExceptionState` | `1` | The context is in an exceptional state.

## Member Function Documentation

### QScriptContext::~QScriptContext ()

Destroys this 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.

See also setActivationObject(), argument(), and argumentsObject().

### QScriptValue QScriptContext::argument ( int index ) const

Returns the function argument at the given index.

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

See also 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()).

See also 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.

See also argument() and 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>`.

See also QScriptEngine::uncaughtExceptionBacktrace().

### QScriptValue QScriptContext::callee () const

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

### QScriptEngine * QScriptContext::engine () const

Returns the 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.

### 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.

See also activationObject().

### void QScriptContext::setThisObject ( const QScriptValue & thisObject )

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

See also thisObject().

### ExecutionState QScriptContext::state () const

Returns the execution state of this QScriptContext.

### QScriptValue QScriptContext::thisObject () const

Returns the `this' object associated with this QScriptContext.

See also setThisObject().

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

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

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

See also throwValue() and state().

### QScriptValue QScriptContext::throwError ( const QString & text )

This is an overloaded member function, provided for convenience.

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

See also throwValue() and state().

### QScriptValue QScriptContext::throwValue ( const QScriptValue & value )

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

See also throwError() and state().