A component that can be added to a hierarchy that won't add its sub-components

until it is visible.


git-svn-id: https://samskivert.googlecode.com/svn/trunk@1435 6335cc39-0255-0410-8fd6-9bcaacd3b74c

projects/samskivert/src/java/com/samskivert/swing/LazyComponent.java

@@ -0,0 +1,71 @@
+//
+// $Id: LazyComponent.java,v 1.1 2004/05/21 20:57:12 ray Exp $
+
+package com.samskivert.swing;
+
+import java.awt.BorderLayout;
+import java.awt.Container;
+
+import javax.swing.JComponent;
+
+/**
+ * A component that doesn't actually create its content until it is
+ * visible and actually showing. This was made to support lazy-creation
+ * in JTabbedPane, since normally adding a compent to a JTabbedPane
+ * creates each component and their associated controllers.
+ */
+public class LazyComponent extends JComponent
+{
+    /**
+     * An interface for creating the actual content that will live
+     * in this component.
+     */
+    public interface ContentCreator
+    {
+        /**
+         * Create the content at the time that it is needed.
+         */
+        public JComponent createContent ();
+    }
+
+    /**
+     * Create a lazy component.
+     */
+    public LazyComponent (ContentCreator creator)
+    {
+        _creator = creator;
+    }
+
+    // documentation inherited
+    public void addNotify ()
+    {
+        super.addNotify();
+
+        checkCreate();
+    }
+
+    // documentation inherited
+    public void setVisible (boolean vis)
+    {
+        super.setVisible(vis);
+
+        checkCreate();
+    }
+
+    /**
+     * Check to see if we should now create the content.
+     */
+    protected void checkCreate ()
+    {
+        if (_creator != null && isShowing()) {
+            // ideally, we would replace ourselves in our parent, but that
+            // doesn't seem to work in JTabbedPane
+            setLayout(new BorderLayout());
+            add(_creator.createContent(), BorderLayout.CENTER);
+            _creator = null;
+        }
+    }
+
+    /** The content creator. */
+    protected ContentCreator _creator;
+}