9.4 The DesktopManager Interface

This interface is responsible for much of the management of internal frames contained by JDesktopPanes. It allows an L&F to define exactly how it wants to manage things such as frame activation, movement, and iconification. Most of the methods in InternalFrameUI implementations should delegate to a DesktopManager object. As described earlier, DesktopManagers are contained by JDesktopPane objects and are intended to be set by the L&F. You can also create your own variations on the supplied implementations to provide custom behavior, as shown in the example that concludes this chapter.

9.4.1 Methods

The majority of the methods in this interface act on a given JInternalFrame. However, those methods that could be applied to other types of components do not restrict the parameter unnecessarily (they accept any JComponent), despite the fact that they are typically used only with JInternalFrames. If you implement your own DesktopManager or other L&F classes, you may find a need for this flexibility.

public abstract void activateFrame( JInternalFrame f )

Called to indicate that the specified frame should become active (is gaining focus).

public abstract void beginDraggingFrame( JComponent f )

Called to indicate that the specified frame is now being dragged. The given component is normally a JInternalFrame.

public abstract void beginResizingFrame( JComponent f, int direction)

Called to indicate that the specified frame will be resized. The direction comes from SwingConstants and must be NORTH, SOUTH, EAST, WEST, NORTH_EAST, NORTH_WEST, SOUTH_EAST, or SOUTH_WEST, representing the edge or corner being dragged (although this value is currently ignored by all provided implementations). The given component is normally a JInternalFrame. When resizing is complete, endResizingFrame( ) is called.

public abstract void closeFrame( JInternalFrame f )

Called to indicate that the specified frame should be closed.

public abstract void deactivateFrame( JInternalFrame f )

Called to indicate that the specified frame is no longer active (has lost focus).

public abstract void deiconifyFrame( JInternalFrame f )

Called to indicate that the specified frame should no longer be iconified.

public abstract void dragFrame( JComponent f, int newX, int newY)

Called to indicate that the specified frame should be moved from its current location to the newly specified coordinates. The given component is normally a JInternalFrame.

public abstract void endDraggingFrame( JComponent f )

Called to indicate that the specified frame is no longer being dragged. The given component is normally a JInternalFrame.

public abstract void endResizingFrame( JComponent f )

Called to indicate that the specified frame is no longer being resized. The given component is normally a JInternalFrame.

public abstract void iconifyFrame( JInternalFrame f )

Called to indicate that the specified frame should be iconified.

public abstract void maximizeFrame( JInternalFrame f )

Called to indicate that the specified frame should be maximized.

public abstract void minimizeFrame( JInternalFrame f )

Called to indicate that the specified frame should be minimized. Note that this is not the same as iconifying the frame. Typically, calling this method causes the frame to return to its size and position before it was maximized.

public abstract void openFrame( JInternalFrame f )

Called to add a frame and display it at a reasonable location. This is not often called because frames are normally added directly to their parent.

public abstract void resizeFrame( JComponent f, int newX, int newY, int newWidth, int newHeight)

Called to indicate that the specified frame has been resized. Note that resizing is still in progress (many calls to this method may be made while the frame is being resized) after this method completes. The given component is normally a JInternalFrame.

public abstract void setBoundsForFrame( JComponent f, int newX, int newY, int newWidth, int newHeight)

Called to set a new size and location for a frame. The given component will normally be a JInternalFrame.

9.4.2 The DefaultDesktopManager Class

DefaultDesktopManager is a default implementation of the DesktopManager interface. It serves as the base class for the Windows and Motif L&Fs, while the Metal L&F uses it without modification. In this section, we'll give a brief explanation of how each of the methods in the interface is implemented by this class.

9.4.2.1 Methods

public void activateFrame( JInternalFrame f )

Call setSelected(false) on all other JInternalFrames contained by the specified frame's parent that are in the same layer as the given frame. It then moves the given frame to the front of its layer and selects it.

public void closeFrame( JInternalFrame f )

Remove the given frame from its parent. It also removes the frame's icon (if displayed). It sets the frame's previous bounds to null.

public void deiconifyFrame( JInternalFrame f )

Remove the given frame's icon from its parent and add the frame itself in its place. This method then tries to select the given frame if it can receive focus.

public void dragFrame( JComponent f, int newX, int newY)

Call setBoundsForFrame( ) with the given location and current dimensions.

public void iconifyFrame( JInternalFrame f )

Remove the given frame from its parent and add the frame's desktop icon. Before adding the icon, it checks to see if it has ever been iconified. If not, it calls getBoundsForIconOf( ) to set the icon's bounds. This is done only once for a given frame, ensuring that each time a frame is iconified, it returns to the same location on the desktop.

public void maximizeFrame( JInternalFrame f )

Maximize the given frame so that it fills its parent. This method also saves the frame's previous bounds for use in minimizeFrame( ). Once the frame has been maximized, it is also selected. This method can be called on an iconified frame, causing it to be deiconified and maximized.

public void minimizeFrame( JInternalFrame f )

Set the frame's bounds to its previous bounds. If there are no previous bounds (previous bounds are set by calling maximizeFrame( )), the frame is not resized.

public void openFrame( JInternalFrame f )

Get the desktop icon for the given frame. If the icon's parent is non-null, the icon is removed from the parent, and the frame is added. If its parent is null, this method does nothing.

public void resizeFrame( JComponent f, int newX, int newY, int newWidth, int newHeight)

Call setBoundsForFrame( ) with the given location and dimensions.

public void setBoundsForFrame( JComponent f, int newX, int newY, int newWidth, int newHeight)

Move and resize the given frame (using setBounds( )) and validate the frame if the size was actually changed.

public void beginDraggingFrame( JComponent f )

public void beginResizingFrame( JComponent f, int direction)

public void endDraggingFrame( JComponent f )

public void endResizingFrame( JComponent f )

Provide support for faster dragging if the desktop's dragMode requires it.

public void deactivateFrame( JInternalFrame f )

If the frame was selected, deselect it.

9.4.2.2 Protected methods

This default implementation provides several convenience methods, which it uses in the methods described above. The methods relate to desktop icon management and the management of a frame's previous size (when maximized). If you subclass DefaultDesktopManager, these methods will probably be of use to you.

The frame's previous bounds and an indication of whether it has ever been iconified are stored in client properties on the frame itself.^[3] The property names used are previousBounds (which holds a Rectangle) and wasIconOnce (which holds a Boolean).

^[3] See Section 3.5.9 for an explanation of JComponent's client property feature.

protected Rectangle getBoundsForIconOf( JInternalFrame f )

Get the bounds for the given frame's icon. The width and height are taken directly from the size of the icon. The icon is placed in the lower-left corner of the desktop. If an icon has already been placed in this corner, the icon is placed directly to the right, continuing until an unclaimed position along the bottom of the frame is found. If there is no space along the bottom, a new row of icons is started directly above the first row. Once a frame has been iconified, its icon's location is set, and the icon always returns to the same spot (unless it is moved by the user).

protected Rectangle getPreviousBounds( JInternalFrame f )

Return the frame's previous bounds (set when the frame is maximized). These bounds are retrieved from the frame's previousBounds client property.

protected void removeIconFor( JInternalFrame f )

Remove the given frame's icon from its parent and repaint the region under the icon.

protected void setPreviousBounds( JInternalFrame f, Rectangle r)

Save the previous bounds of a frame. This is done by saving the frame's previous bounds in the frame itself, using the client property, previousBounds. This is generally called by maximizeFrame( ), with the data being used in a subsequent minimizeFrame( ) call.

protected void setWasIcon( JInternalFrame f, Boolean value)

Called by iconifyFrame( ) to indicate whether the frame has, at some time, been iconified. This is done by saving the boolean value in the frame itself, using the client property wasIconOnce. This is used to determine whether the icon's bounds have been defined.

protected boolean wasIcon( JInternalFrame f )

Determine whether a frame has ever been iconified (if it has, bounds are already defined for the icon). This is done by returning the wasIconOnce client property on the frame.