private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int yoff,
            boolean scalingRequired, Rect dirty) {
       .......
       canvas = mSurface.lockCanvas(dirty);    //Obtain and Lock Canvas Drawing Objects through Surface Objects
       .......
       mView.draw(canvas);  //Drawing from DecorView, which is the root view of the whole Window s, will result in drawing the whole tree.
       .......
       surface.unlockCanvasAndPost(canvas);    //Release the Canvas lock and notify Surface Flinger to update the area
       .......
}

public void draw(Canvas canvas) {
	final int privateFlags = mPrivateFlags;
	final boolean dirtyOpaque = (privateFlags & PFLAG_DIRTY_MASK) == PFLAG_DIRTY_OPAQUE &&
			(mAttachInfo == null || !mAttachInfo.mIgnoreDirtyState);
	mPrivateFlags = (privateFlags & ~PFLAG_DIRTY_MASK) | PFLAG_DRAWN;

	/*
	 * Draw traversal performs several drawing steps which must be executed
	 * in the appropriate order:
	 *
	 *      1. Draw the background
	 *      2. If necessary, save the canvas' layers to prepare for fading
	 *      3. Draw view's content
	 *      4. Draw children
	 *      5. If necessary, draw the fading edges and restore layers
	 *      6. Draw decorations (scrollbars for instance)
	 */

	// Step 1, draw the background, if needed
	int saveCount;

	if (!dirtyOpaque) {
		drawBackground(canvas);//Drawing background
	}

	// skip step 2 & 5 if possible (common case)
	final int viewFlags = mViewFlags;
	boolean horizontalEdges = (viewFlags & FADING_EDGE_HORIZONTAL) != 0;
	boolean verticalEdges = (viewFlags & FADING_EDGE_VERTICAL) != 0;
	if (!verticalEdges && !horizontalEdges) {//The fading Edge property is not set, and the gradient projection effect is not set.
		// Step 3, draw the content
		if (!dirtyOpaque) {
			onDraw(canvas);
		}

		// Step 4, draw the children
		dispatchDraw(canvas);

		// Step 6, draw decorations (scrollbars)
		onDrawScrollBars(canvas);

		if (mOverlay != null && !mOverlay.isEmpty()) {
			mOverlay.getOverlayView().dispatchDraw(canvas);
		}

		// we're done...
		return;
	}
	...//Processing settings for gradient projection effects
}

protected void onDraw(Canvas canvas) {
	if (mDivider == null) {
		return;
	}

	if (mOrientation == VERTICAL) {
		drawDividersVertical(canvas);
	} else {
		drawDividersHorizontal(canvas);
	}
}

void drawDividersVertical(Canvas canvas) {
	final int count = getVirtualChildCount();
	for (int i = 0; i < count; i++) {
		final View child = getVirtualChildAt(i);

		if (child != null && child.getVisibility() != GONE) {
			if (hasDividerBeforeChildAt(i)) {
				final LayoutParams lp = (LayoutParams) child.getLayoutParams();
				final int top = child.getTop() - lp.topMargin - mDividerHeight;
				drawHorizontalDivider(canvas, top);
			}
		}
	}

	if (hasDividerBeforeChildAt(count)) {
		final View child = getVirtualChildAt(count - 1);
		int bottom = 0;
		if (child == null) {
			bottom = getHeight() - getPaddingBottom() - mDividerHeight;
		} else {
			final LayoutParams lp = (LayoutParams) child.getLayoutParams();
			bottom = child.getBottom() + lp.bottomMargin;
		}
		drawHorizontalDivider(canvas, bottom);
	}
}