* @attr ref android.R.styleable#ViewGroup_clipChildren
* @attr ref android.R.styleable#ViewGroup_clipToPadding
* @attr ref android.R.styleable#ViewGroup_layoutAnimation
* @attr ref android.R.styleable#ViewGroup_animationCache
* @attr ref android.R.styleable#ViewGroup_persistentDrawingCache
* @attr ref android.R.styleable#ViewGroup_alwaysDrawnWithCache
* @attr ref android.R.styleable#ViewGroup_addStatesFromChildren
* @attr ref android.R.styleable#ViewGroup_descendantFocusability
* @attr ref android.R.styleable#ViewGroup_animateLayoutChanges
*/
public abstract class ViewGroup extends View implements ViewParent, ViewManager {

/**
* Adds a child view. If no layout parameters are already set on the child, the
* default parameters for this ViewGroup are set on the child.
*
* @param child the child view to add
*
* @see #generateDefaultLayoutParams()
*/
public void addView(View child) {
addView(child, -1);
}

/**
* Adds a child view. If no layout parameters are already set on the child, the
* default parameters for this ViewGroup are set on the child.
*
* @param child the child view to add
* @param index the position at which to add the child
*
* @see #generateDefaultLayoutParams()
*/
public void addView(View child, int index) {
LayoutParams params = child.getLayoutParams();
if (params == null) {
params = generateDefaultLayoutParams();
if (params == null) {
throw new IllegalArgumentException("generateDefaultLayoutParams() cannot return null");
}
}
addView(child, index, params);
}

/**
* Adds a child view with this ViewGroup's default layout parameters and the
* specified width and height.
*
* @param child the child view to add
*/
public void addView(View child, int width, int height) {
final LayoutParams params = generateDefaultLayoutParams();
params.width = width;
params.height = height;
addView(child, -1, params);
}

/**
* Adds a child view with the specified layout parameters.
*
* @param child the child view to add
* @param params the layout parameters to set on the child
*/
public void addView(View child, LayoutParams params) {
addView(child, -1, params);
}

/**
* Adds a child view with the specified layout parameters.
*
* @param child the child view to add
* @param index the position at which to add the child
* @param params the layout parameters to set on the child
*/
public void addView(View child, int index, LayoutParams params) {
if (DBG) {
System.out.println(this + " addView");
}

// addViewInner() will call child.requestLayout() when setting the new LayoutParams
// therefore, we call requestLayout() on ourselves before, so that the child's request
// will be blocked at our level
requestLayout();
invalidate(true);
addViewInner(child, index, params, false);
}

public void removeView(View view) {
removeViewInternal(view);
requestLayout();
invalidate(true);
}

/**
* Removes a view during layout. This is useful if in your onLayout() method,
* you need to remove more views.
*
* @param view the view to remove from the group
*/
public void removeViewInLayout(View view) {
removeViewInternal(view);
}

/**
* Removes a range of views during layout. This is useful if in your onLayout() method,
* you need to remove more views.
*
* @param start the index of the first view to remove from the group
* @param count the number of views to remove from the group
*/
public void removeViewsInLayout(int start, int count) {
removeViewsInternal(start, count);
}

/**
* Removes the view at the specified position in the group.
*
* @param index the position in the group of the view to remove
*/
public void removeViewAt(int index) {
removeViewInternal(index, getChildAt(index));
requestLayout();
invalidate(true);
}

/**
* Removes the specified range of views from the group.
*
* @param start the first position in the group of the range of views to remove
* @param count the number of views to remove
*/
public void removeViews(int start, int count) {
removeViewsInternal(start, count);
requestLayout();
invalidate(true);
}

private void removeViewInternal(View view) {
final int index = indexOfChild(view);
if (index >= 0) {
removeViewInternal(index, view);
}
}

private void removeViewInternal(int index, View view) {

if (mTransition != null) {
mTransition.removeChild(this, view);
}

boolean clearChildFocus = false;
if (view == mFocused) {
view.clearFocusForRemoval();
clearChildFocus = true;
}

if (view.getAnimation() != null ||
(mTransitioningViews != null && mTransitioningViews.contains(view))) {
addDisappearingView(view);
} else if (view.mAttachInfo != null) {
view.dispatchDetachedFromWindow();
}

onViewRemoved(view);

needGlobalAttributesUpdate(false);

removeFromArray(index);

if (clearChildFocus) {
clearChildFocus(view);
}
}

/**
* Sets the LayoutTransition object for this ViewGroup. If the LayoutTransition object is
* not null, changes in layout which occur because of children being added to or removed from
* the ViewGroup will be animated according to the animations defined in that LayoutTransition
* object. By default, the transition object is null (so layout changes are not animated).
*
* @param transition The LayoutTransition object that will animated changes in layout. A value
* of null means no transition will run on layout changes.
* @attr ref android.R.styleable#ViewGroup_animateLayoutChanges
*/
public void setLayoutTransition(LayoutTransition transition) {
if (mTransition != null) {
mTransition.removeTransitionListener(mLayoutTransitionListener);
}
mTransition = transition;
if (mTransition != null) {
mTransition.addTransitionListener(mLayoutTransitionListener);
}
}

/**
* Gets the LayoutTransition object for this ViewGroup. If the LayoutTransition object is
* not null, changes in layout which occur because of children being added to or removed from
* the ViewGroup will be animated according to the animations defined in that LayoutTransition
* object. By default, the transition object is null (so layout changes are not animated).
*
* @return LayoutTranstion The LayoutTransition object that will animated changes in layout.
* A value of null means no transition will run on layout changes.
*/
public LayoutTransition getLayoutTransition() {
return mTransition;
}

private void removeViewsInternal(int start, int count) {
final View focused = mFocused;
final boolean detach = mAttachInfo != null;
View clearChildFocus = null;

final View[] children = mChildren;
final int end = start + count;

for (int i = start; i < end; i++) {
final View view = children[i];

if (mTransition != null) {
mTransition.removeChild(this, view);
}

if (view == focused) {
view.clearFocusForRemoval();
clearChildFocus = view;
}

if (view.getAnimation() != null ||
(mTransitioningViews != null && mTransitioningViews.contains(view))) {
addDisappearingView(view);
} else if (detach) {
view.dispatchDetachedFromWindow();
}

needGlobalAttributesUpdate(false);

onViewRemoved(view);
}

removeFromArray(start, count);

if (clearChildFocus != null) {
clearChildFocus(clearChildFocus);
}
}

/**
* Call this method to remove all child views from the
* ViewGroup.
*/
public void removeAllViews() {
removeAllViewsInLayout();
requestLayout();
invalidate(true);
}

/**
* Called by a ViewGroup subclass to remove child views from itself,
* when it must first know its size on screen before it can calculate how many
* child views it will render. An example is a Gallery or a ListView, which
* may "have" 50 children, but actually only render the number of children
* that can currently fit inside the object on screen. Do not call
* this method unless you are extending ViewGroup and understand the
* view measuring and layout pipeline.
*/
public void removeAllViewsInLayout() {
final int count = mChildrenCount;
if (count = 0; i--) {
final View view = children[i];

if (mTransition != null) {
mTransition.removeChild(this, view);
}

if (view == focused) {
view.clearFocusForRemoval();
clearChildFocus = view;
}

if (view.getAnimation() != null ||
(mTransitioningViews != null && mTransitioningViews.contains(view))) {
addDisappearingView(view);
} else if (detach) {
view.dispatchDetachedFromWindow();
}

onViewRemoved(view);

view.mParent = null;
children[i] = null;
}

if (clearChildFocus != null) {
clearChildFocus(clearChildFocus);
}
}

/**
* Finishes the removal of a detached view. This method will dispatch the detached from
* window event and notify the hierarchy change listener.
*
* @param child the child to be definitely removed from the view hierarchy
* @param animate if true and the view has an animation, the view is placed in the
* disappearing views list, otherwise, it is detached from the window
*
* @see #attachViewToParent(View, int, android.view.ViewGroup.LayoutParams)
* @see #detachAllViewsFromParent()
* @see #detachViewFromParent(View)
* @see #detachViewFromParent(int)
*/
protected void removeDetachedView(View child, boolean animate) {
if (mTransition != null) {
mTransition.removeChild(this, child);
}

if (child == mFocused) {
child.clearFocus();
}

if ((animate && child.getAnimation() != null) ||
(mTransitioningViews != null && mTransitioningViews.contains(child))) {
addDisappearingView(child);
} else if (child.mAttachInfo != null) {
child.dispatchDetachedFromWindow();
}

onViewRemoved(child);
}

/**
* Returns the view at the specified position in the group.
*
* @param index the position at which to get the view from
* @return the view at the specified position or null if the position
* does not exist within the group
*/
public View getChildAt(int index) {
if (index < 0 || index >= mChildrenCount) {
return null;
}
return mChildren[index];
}

public class TextView extends View implements ViewTreeObserver.OnPreDrawListener {
。。。
}

public class LinearLayout extends ViewGroup {
public static final int HORIZONTAL = 0;
public static final int VERTICAL = 1;
。。。
}

public class FrameLayout extends ViewGroup {
...
}

public class RelativeLayout extends ViewGroup {
private static final String LOG_TAG = "RelativeLayout";

private static final boolean DEBUG_GRAPH = false;
...
}

public class AbsoluteLayout extends ViewGroup {
public AbsoluteLayout(Context context) {
super(context);
}
}
...