android: use onDraw for element drawing in CanvasElement interface

Use onDraw to override the drawing to canvas. CommonCanvasElement
uses the draw method to call onDraw depending on visibility.

Change-Id: Id98991935168caab9d39665e72f33cfb3a91d8dc

android/experimental/LOAndroid3/src/java/org/libreoffice/canvas/CanvasElement.java

@@ -17,11 +17,21 @@ import android.graphics.Canvas;
  */
 public interface CanvasElement {
     /**
-     * Called when the element needs to be draw no the canvas.
+     * Called when the element needs to be draw no the canvas. This method
+     * should call onDraw when conditions to draw are satisfied.
+     *
      * @param canvas - the canvas
      */
     void draw(Canvas canvas);
 
+    /**
+     * Called inside draw if the element is visible. Override this method to
+     * draw the element on the canvas.
+     *
+     * @param canvas - the canvas
+     */
+    void onDraw(Canvas canvas);
+
     /**
      * Hit test - returns true if the object has been hit
      * @param x - x coordinate of the

android/experimental/LOAndroid3/src/java/org/libreoffice/canvas/CommonCanvasElement.java

@@ -1,5 +1,7 @@
 package org.libreoffice.canvas;
 
+import android.graphics.Canvas;
+
 /**
  * Common implementation to canvas elements.
  */
@@ -16,4 +18,11 @@ public abstract class CommonCanvasElement implements CanvasElement {
     public void setVisible(boolean visible) {
         mVisible = visible;
     }
+
+    @Override
+    public void draw(Canvas canvas) {
+        if (isVisible()) {
+            onDraw(canvas);
+        }
+    }
 }

android/experimental/LOAndroid3/src/java/org/libreoffice/canvas/GraphicSelection.java

@@ -103,7 +103,7 @@ public class GraphicSelection extends CommonCanvasElement {
      * @see org.libreoffice.canvas.CanvasElement#draw(android.graphics.Canvas)
      */
     @Override
-    public void draw(Canvas canvas) {
+    public void onDraw(Canvas canvas) {
         canvas.drawRect(mDrawRectangle, mPaintStroke);
         if (mType != DragType.NONE) {
             canvas.drawRect(mDrawRectangle, mPaintFill);

android/experimental/LOAndroid3/src/java/org/libreoffice/canvas/GraphicSelectionHandle.java

@@ -71,7 +71,7 @@ public class GraphicSelectionHandle extends CommonCanvasElement {
      * @see org.libreoffice.canvas.CanvasElement#draw(android.graphics.Canvas)
      */
     @Override
-    public void draw(Canvas canvas) {
+    public void onDraw(Canvas canvas) {
         if (mSelected) {
             drawFilledCircle(canvas, mPosition.x, mPosition.y, mRadius, mStrokePaint, mSelectedFillPaint);
         } else {