Class 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.
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      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 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 void reset()
      Immediately wipes out all native level state associated with all callbacks.
      static 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.
    • Constructor Detail

      • 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.
        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.
        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.
        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
    • Method Detail

      • 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.