PATHJava Developer Documentation > Mac OS Runtime for Java > JManager > Programming With JManager

Displaying Frames

As explained earlier, a Java program displays graphical output in virtual windows called frames. Since frames correspond to Mac OS windows, you can manipulate them in a similar manner (for example, create or destroy frames, resize them, and so on).

In order to communicate between the abstract frames and the actual Mac OS windows, you must designate a number of application-defined callback functions. Many of these functions correspond to similar Mac OS Toolbox functions. The application-defined functions and their corresponding Mac OS Toolbox functions are shown in Table 1-1. For details of the structure of these functions, see Application-Defined Functions.

**Table 1-1** Application-defined frame functions
Frame function	Description	Corresponding Mac OS Toolbox function
`MyRequestFrame`	Creates a new window	`GetNewCWindow` , `NewCWindow` , `GetNewWindow` , or `NewWindow`
`MyReleaseFrame`	Disposes of a window	`DisposeWindow`
`MyResizeRequest`	Requests that a window be resized	`SizeWindow`
`MyInvalRect`	Invalidates a portion of a window	`InvalRect`
`MyShowHide`	Shows or hides a window	`ShowHide` or `ShowWindow`and `HideWindow`
`MySetTitle`	Sets the window title bar	`SetWTitle`
`MyCheckUpdate`	Checks to see if a window update is necessary	`CheckUpdate`or `BeginUpdate` and `EndUpdate`
`MyFrameReorder`	Changes the ordering of the frame (bring to front, send to back, etc)	`BringToFront` or `SendBehind`
`MySetResizeable`	Sets whether a frame is resizeable or not	No corresponding function, although the state set by this function affects whether your `DoGrowWindow` callback calls the `SizeWindow` function.

Typically the bulk of an application-defined frame function prepares a call to the corresponding Mac OS Toolbox function. For example, assuming that the application uses the functions in Listing 1-8 and Listing 1-9, you can use the callback function in Listing 1-10 to set the window title.

Listing 1-10 A callback function to change the title of a window



 
void MySetTitle(JMFrameRef frame, JMTextRef titleObj)

{

    Handle title; 

    Str255 ptitle;



    title = JMTextToMacOSCStringHandle(titleObj);

    Hlock(title);



    convertToPascalString(*title, &ptitle); /* this is a dummy utility */



    WindowPtr win = getFrameWindow(frame);

    if (win)

        SetWTitle(win, ptitle);



    HUnlock(title);

    DisposeHandle(title); 

}

Since the Mac OS Toolbox function SetWTitle requires a Pascal string, you must convert the handle title before calling SetWTitle .