Java SWT - listen if new children are added to the Composite?
events, java, swt, user-interface
Solution
The only way to add custom `MyComposite` and create custom `ChildEvent` as well as `ChildEventListener` interface. `MyComposite` is capable of registering listeners of `ChildEvent` and fire this event when a child `Composite` is created.
import org.eclipse.swt.SWT;
import org.eclipse.swt.events.TypedEvent;
import org.eclipse.swt.internal.SWTEventListener;
import org.eclipse.swt.widgets.*;
/*
* This example demonstrates the minimum amount of code required
* to open an SWT Shell and process the events.
*/
public class HelloWorld1 {
public static void main (String [] args) {
Display display = new Display ();
Shell shell = new HelloWorld1 ().open (display);
while (!shell.isDisposed ()) {
if (!display.readAndDispatch ()) display.sleep ();
}
display.dispose ();
}
public Shell open (Display display) {
Shell shell = new Shell (display);
MyComposite parent = new MyComposite(shell, SWT.NONE);
parent.addChildEventListener(new ChildEventListener() {
@Override
public void add(ChildEvent e) {
System.out.println("Child added.");
}
});
MyComposite child = new MyComposite(parent, SWT.NONE);
// shell.open ();
return shell;
}
}
class MyComposite extends Composite {
ChildEventListener[] childEventListeners = new ChildEventListener[0];
public MyComposite(Composite parent, int style) {
super(parent, style);
if (parent instanceof MyComposite){
((MyComposite)parent).fireChildEvent(new ChildEvent(this));
}
}
public void addChildEventListener (ChildEventListener listener) {
checkWidget();
if (listener == null) SWT.error (SWT.ERROR_NULL_ARGUMENT);
ChildEventListener[] newChildEventListeners = new ChildEventListener[childEventListeners.length + 1];
System.arraycopy(childEventListeners, 0, newChildEventListeners, 0, childEventListeners.length);
childEventListeners = newChildEventListeners;
childEventListeners[childEventListeners.length - 1] = listener;
}
public void removeChildEventListener (ChildEventListener listener) {
if (childEventListeners.length == 0) return;
int index = -1;
for (int i = 0; i < childEventListeners.length; i++) {
if (listener == childEventListeners[i]){
index = i;
break;
}
}
if (index == -1) return;
if (childEventListeners.length == 1) {
childEventListeners = new ChildEventListener[0];
return;
}
ChildEventListener[] newChildEventListeners = new ChildEventListener[childEventListeners.length - 1];
System.arraycopy (childEventListeners, 0, newChildEventListeners, 0, index);
System.arraycopy (childEventListeners, index + 1, newChildEventListeners, index, childEventListeners.length - index - 1);
childEventListeners = newChildEventListeners;
}
public void fireChildEvent(ChildEvent event){
for (int i = 0; i < childEventListeners.length; i++) {
childEventListeners[i].add (event);
}
}
}
interface ChildEventListener extends SWTEventListener {
public void add(ChildEvent e);
}
class ChildEvent extends TypedEvent {
public ChildEvent(Widget widget) {
super(widget);
// TODO Auto-generated constructor stub
}
}
Problem
I have a `Composite`. In SWT the children are added, by children, no by parents: ``` Composite parent = new Composite(shell, SWT.none); Composite child = new Composite(parent, SWT.none); ``` That means, that inside of the parent I do not know, in which way and when the children are added to their parents. QUESTION: Inside of the parent I need to know, when new children are added to the parent. Is there any way to register an `onChildAddListener` or any `add()` method to override?