原博文地址：http://blog.csdn.net/baidu_nod/article/details/38815269

原理是在onMeasure中得到隱藏內容的高度，點選這個view的時候對隱藏的view startAnimation,讓它的高度從0增長到onMeasure得到的這個View的measureHeight

具體這樣寫:

1. publicclass ExpandableLayout extends LinearLayout {  
2.     private Context mContext;  
3.     private LinearLayout mHandleView;  
4.     private
    RelativeLayout mContentView;  
5.     private ImageView mIconExpand;  
6.     int mContentHeight = 0;  
7.     int mTitleHeight = 0;  
8.     privateboolean isExpand;  
9.     private Animation animationDown;  
10.     private Animation animationUp;  
11.     public ExpandableLayout(Context context, AttributeSet attrs) {  
12.         super(context, attrs);  
13.         this.mContext = context;  
14.     }  
15.     @Override
16.     protectedvoid onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  
17.         if (this.mContentHeight == 0) {  
18.             this.mContentView.measure(widthMeasureSpec, 0);  
19.             this.mContentHeight = 
    this.mContentView.getMeasuredHeight();  
20.         }  
21.         if (this.mTitleHeight == 0) {  
22.             this.mHandleView.measure(widthMeasureSpec, 0);  
23.             this.mTitleHeight = this.mHandleView.getMeasuredHeight();  
24.         }  
25.         super.onMeasure(widthMeasureSpec, heightMeasureSpec);  
26.     }  
27.     @Override
28.     protectedvoid onFinishInflate() {  
29.         super.onFinishInflate();  
30.         this.mHandleView = (LinearLayout) this
31.                 .findViewById(R.id.collapse_value);  
32.         this.mContentView = (RelativeLayout) this.findViewById(R.id.expand_value);  
33.         this.mIconExpand = (ImageView) this.findViewById(R.id.icon_value);  
34.         this.mHandleView.setOnClickListener(new ExpandListener());  
35.         this.mContentView.setOnClickListener(new ExpandListener());  
36.         mContentView.setVisibility(View.GONE);  
37.     }  
38.     privateclass ExpandListener implements View.OnClickListener {  
39.         @Override
40.         publicfinalvoid onClick(View paramView) {  
41.             //clearAnimation是view的方法
42.             clearAnimation();  
43.             if (!isExpand) {  
44.                 if (animationDown == null) {  
45.                     animationDown = new DropDownAnim(mContentView,  
46.                             mContentHeight, true);  
47.                     animationDown.setDuration(200); // SUPPRESS CHECKSTYLE
48.                 }  
49.                 startAnimation(animationDown);  
50.                 mContentView.startAnimation(AnimationUtils.loadAnimation(  
51.                         mContext, R.anim.animalpha));  
52.                 mIconExpand.setImageResource(R.drawable.update_detail_up);  
53.                 isExpand = true;  
54.             } else {  
55.                 isExpand = false;  
56.                 if (animationUp == null) {  
57.                     animationUp = new DropDownAnim(mContentView,  
58.                             mContentHeight, false);  
59.                     animationUp.setDuration(200); // SUPPRESS CHECKSTYLE
60.                 }  
61.                 startAnimation(animationUp);  
62.                 mIconExpand.setImageResource(R.drawable.update_detail_down);  
63.             }  
64.         }  
65.     }  
66.     class DropDownAnim extends Animation {  
67.         /** 目標的高度 */
68.         privateint targetHeight;  
69.         /** 目標view */
70.         private View view;  
71.         /** 是否向下展開 */
72.         privateboolean down;  
73.         /** 
74.          * 構造方法 
75.          *  
76.          * @param targetview 
77.          *            需要被展現的view 
78.          * @param vieweight 
79.          *            目的高 
80.          * @param isdown 
81.          *            true:向下展開，false:收起 
82.          */
83.         public DropDownAnim(View targetview, int vieweight, boolean isdown) {  
84.             this.view = targetview;  
85.             this.targetHeight = vieweight;  
86.             this.down = isdown;  
87.         }  
88.         //down的時候，interpolatedTime從0增長到1，這樣newHeight也從0增長到targetHeight
89.         @Override
90.         protectedvoid applyTransformation(float interpolatedTime,  
91.                 Transformation t) {  
92.             int newHeight;  
93.             if (down) {  
94.                 newHeight = (int) (targetHeight * interpolatedTime);  
95.             } else {  
96.                 newHeight = (int) (targetHeight * (1 - interpolatedTime));  
97.             }  
98.             view.getLayoutParams().height = newHeight;  
99.             view.requestLayout();  
100.             if (view.getVisibility() == View.GONE) {  
101.                 view.setVisibility(View.VISIBLE);  
102.             }  
103.         }  
104.         @Override
105.         publicvoid initialize(int width, int height, int parentWidth,  
106.                 int parentHeight) {  
107.             super.initialize(width, height, parentWidth, parentHeight);  
108.         }  
109.         @Override
110.         publicboolean willChangeBounds() {  
111.             returntrue;  
112.         }  
113.     }  
114. }  

1. <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
2.     xmlns:tools="http://schemas.android.com/tools"
3.     android:layout_width="match_parent"
4.     android:layout_height="match_parent"
5.     android:background="#FFFFFF" >  
6.     <com.example.view.ExpandableLayout  
7.         android:id="@+id/app_detail_safety_info"
8.         android:layout_width="fill_parent"
9.         android:layout_height="wrap_content"
10.         android:orientation="vertical" >  
11.         <LinearLayout  
12.             android:id="@+id/collapse_value"
13.             android:layout_width="fill_parent"
14.             android:layout_height="34dip"
15.             android:layout_marginLeft="14dip"
16.             android:gravity="center_vertical"
17.             android:orientation="horizontal" >  
18.             <TextView  
19.                 android:layout_width="wrap_content"
20.                 android:layout_height="wrap_content"
21.                 android:layout_marginLeft="30dp"
22.                 android:text="點選我會顯示隱藏的內容"
23.                 android:textColor="#000000"
24.                 android:textSize="18sp" >  
25.             </TextView>  
26.             <LinearLayout  
27.                 android:layout_width="fill_parent"
28.                 android:layout_height="fil