Package org.eclipse.swt.internal

Class Callback

java.lang.Object
org.eclipse.swt.internal.Callback
public class Callback extends Object
Instances of this class represent entry points into Java which can be invoked from operating system level callback routines.

IMPORTANT: A callback is only valid when invoked on the thread which created it. The results are undefined (and typically bad) when a callback is passed out to the operating system (or other code) in such a way that the callback is called from a different thread.

  • Constructor Summary

    Constructors
    Constructor
    Description
    Callback(Object object, String method, int argCount)
    Constructs a new instance of this class given an object to send the message to, a string naming the method to invoke and an argument count.
    Callback(Object object, String method, int argCount, boolean isArrayBased)
    Constructs a new instance of this class given an object to send the message to, a string naming the method to invoke, an argument count and a flag indicating whether or not the arguments will be passed in an array.
    Callback(Object object, String method, int argCount, boolean isArrayBased, long errorResult)
    Constructs a new instance of this class given an object to send the message to, a string naming the method to invoke, an argument count, a flag indicating whether or not the arguments will be passed in an array and a value to return when an exception happens.
    Callback(Object object, String method, Type returnType, Type[] arguments)
    Register the java method to be a C callback.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    dispose()
    Releases the native level resources associated with the callback, and removes all references between the callback and other objects.
    long
    getAddress()
    Returns the address of a block of machine code which will invoke the callback represented by the receiver.
    static final boolean
    getEnabled()
    Returns whether or not callbacks which are triggered at the native level should cause the messages described by the matching Callback objects to be invoked.
    static int
    getEntryCount()
    Returns the number of times the system has been recursively entered through a callback.
    static String
    getPlatform()
    Returns the SWT platform name.
    static final void
    reset()
    Immediately wipes out all native level state associated with all callbacks.
    static final void
    setEnabled(boolean enable)
    Indicates whether or not callbacks which are triggered at the native level should cause the messages described by the matching Callback objects to be invoked.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • Callback

      public Callback(Object object, String method, int argCount)
      Constructs a new instance of this class given an object to send the message to, a string naming the method to invoke and an argument count. Note that, if the object is an instance of Class it is assumed that the method is a static method on that class.

      Note, do not use this if the method arguments have a double, as arguments will be shifted/corrupted. See Bug 510538. Instead use the following constructor:
      Callback (Object, String, Type, Type [])

      Parameters:
      object - the object to send the message to
      method - the name of the method to invoke
      argCount - the number of arguments that the method takes

    • Callback

      public Callback(Object object, String method, int argCount, boolean isArrayBased)
      Constructs a new instance of this class given an object to send the message to, a string naming the method to invoke, an argument count and a flag indicating whether or not the arguments will be passed in an array. Note that, if the object is an instance of Class it is assumed that the method is a static method on that class.

      Note, do not use this if the method arguments have a double, as arguments will be shifted/corrupted. See Bug 510538. Instead use the following constructor:
      Callback (Object, String, Type, Type [])

      Parameters:
      object - the object to send the message to
      method - the name of the method to invoke
      argCount - the number of arguments that the method takes
      isArrayBased - true if the arguments should be passed in an array and false otherwise

    • Callback

      public Callback(Object object, String method, int argCount, boolean isArrayBased, long errorResult)
      Constructs a new instance of this class given an object to send the message to, a string naming the method to invoke, an argument count, a flag indicating whether or not the arguments will be passed in an array and a value to return when an exception happens. Note that, if the object is an instance of Class it is assumed that the method is a static method on that class.

      Note, do not use this if the method arguments have a double, as arguments will be shifted/corrupted. See Bug 510538. Instead use the following constructor:
      Callback (Object, String, Type, Type [])

      Parameters:
      object - the object to send the message to
      method - the name of the method to invoke
      argCount - the number of arguments that the method takes
      isArrayBased - true if the arguments should be passed in an array and false otherwise
      errorResult - the return value if the java code throws an exception

    • Callback

      public Callback(Object object, String method, Type returnType, Type[] arguments)

      Register the java method to be a C callback. I.e, C will be able to make a call to this java method directly (through callback.c)

      The other constructors hard-code int/long into the method signature:
      long method (long ...)
      Which is suitable for int/long and pointers.
      This constructor is used if you need to use a different return/argument type, e.g double. See Bug 510538

      Note:

      • Array support is not implemented/supported by this constructor. Use other constructors.
      • If the object is an instance of Class it is assumed that the method is a static method on that class.
      • Note, long types are converted to ints on 32 bit system automatically to account for smaller pointers. This means if you use 'long', you need to cast int next to it. like: long /*int*/

      The following types are supported:

      • void (for return values only)
      • int
      • long
      • byte
      • char
      • double
      • float
      • short
      • boolean

      For example if you want to link the following method:
      void myMethod(long /*int*/ arg1, double arg2)
      Then you would call this callback like:
      Callback (this, "myMethod", void.class, new Type []{long.class, double.class});

      Parameters:
      object - the object to send the message to
      method - method the name of the method to invoke
      returnType - specify the type like void.class, long.class, double.class
      arguments - specify the list of arguments like new Type [] {long.class, double.class }

  • Method Details

    • dispose

      public void dispose()
      Releases the native level resources associated with the callback, and removes all references between the callback and other objects. This helps to prevent (bad) application code from accidentally holding onto extraneous garbage.

    • getAddress

      public long getAddress()
      Returns the address of a block of machine code which will invoke the callback represented by the receiver.
      Returns:
      the callback address

    • getPlatform

      public static String getPlatform()
      Returns the SWT platform name.
      Returns:
      the platform name of the currently running SWT

    • getEntryCount

      public static int getEntryCount()
      Returns the number of times the system has been recursively entered through a callback.

      Note: This should not be called by application code.

      Returns:
      the entry count
      Since:
      2.1

    • setEnabled

      public static final void setEnabled(boolean enable)
      Indicates whether or not callbacks which are triggered at the native level should cause the messages described by the matching Callback objects to be invoked. This method is used to safely shut down SWT when it is run within environments which can generate spurious events.

      Note: This should not be called by application code.

      Parameters:
      enable - true if callbacks should be invoked

    • getEnabled

      public static final boolean getEnabled()
      Returns whether or not callbacks which are triggered at the native level should cause the messages described by the matching Callback objects to be invoked. This method is used to safely shut down SWT when it is run within environments which can generate spurious events.

      Note: This should not be called by application code.

      Returns:
      true if callbacks should not be invoked

    • reset

      public static final void reset()
      Immediately wipes out all native level state associated with all callbacks.

      WARNING: This operation is extremely dangerous, and should never be performed by application code.