android自定义控件的最大高度MaxHeightView

android中部分控件具有maxHeight功能，如button，但是对于ViewGroup类的控件，没有此属性，那么，如何为ViewGroup添加一个最大高度的属性呢？其实很简单，主要就是使用onMeasure()函数，在函数中控制高度即可。

先看下效果图：

这是一个dialog，dialog中添加了共有17个button，如果不使用最大高度可控的view，则体验效果不好，可能会完全遮住后边的背景。

java代码实现如下：

  1 package cn.carbs.maxheightview;
  2
  3 import android.content.Context;
  4 import android.content.res.TypedArray;
  5 import android.util.AttributeSet;
  6 import android.util.Log;
  7 import android.view.View;
  8 import android.view.WindowManager;
  9 import android.widget.FrameLayout;
 10
 11 /**
 12  * 先判断是否设定了mMaxHeight，如果设定了mMaxHeight，则直接使用mMaxHeight的值，
 13  * 如果没有设定mMaxHeight，则判断是否设定了mMaxRatio，如果设定了mMaxRatio的值
 14  * 则使用此值与屏幕高度的乘积作为最高高度
 15  * @author Rick.Wang
 16  *
 17  */
 18 public class MaxHeightView extends FrameLayout{
 19
 20     private static final float DEFAULT_MAX_RATIO = 0.4f;
 21     private static final float DEFAULT_MAX_HEIGHT = -1f;
 22
 23     private Context mContext;
 24     private float mMaxHeight = DEFAULT_MAX_HEIGHT;//优先级高
 25     private float mMaxRatio = DEFAULT_MAX_RATIO;//优先级低
 26
 27     public MaxHeightView(Context context) {
 28         this(context, null);
 29     }
 30
 31     public MaxHeightView(Context context, AttributeSet attrs) {
 32         this(context, attrs, 0);
 33     }
 34
 35     public MaxHeightView(Context context, AttributeSet attrs, int defStyle) {
 36         super(context, attrs, defStyle);
 37         mContext = context;
 38
 39         TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.maxHeightView);
 40
 41         final int count = a.getIndexCount();
 42         for (int i = 0; i < count; ++i) {
 43             int attr = a.getIndex(i);
 44             switch (attr) {
 45             case R.styleable.maxHeightView_maxHeightRatio:
 46                 mMaxRatio = a.getFloat(attr, DEFAULT_MAX_RATIO);
 47                 break;
 48             case R.styleable.maxHeightView_maxHeightDimen:
 49                 mMaxHeight = a.getDimension(attr, DEFAULT_MAX_HEIGHT);
 50                 break;
 51             }
 52         }
 53         a.recycle();
 54
 55         if(mMaxHeight < 0){
 56             mMaxHeight = mMaxRatio * (float)getScreenHeight(mContext);
 57         }
 58     }
 59
 60     @Override
 61     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
 62
 63         int heightMode = View.MeasureSpec.getMode(heightMeasureSpec);
 64         int heightSize = View.MeasureSpec.getSize(heightMeasureSpec);
 65
 66         Log.d("wang", "onMeasure heightSize is " + heightSize + " | mMaxHeight is " + mMaxHeight);
 67
 68         if(heightMode == View.MeasureSpec.EXACTLY){
 69             Log.d("wang", "heightMode == View.MeasureSpec.EXACTLY");
 70             heightSize = heightSize <= mMaxHeight ? heightSize : (int)mMaxHeight;
 71         }
 72
 73         if(heightMode == View.MeasureSpec.UNSPECIFIED){
 74             Log.d("wang", "heightMode == View.MeasureSpec.UNSPECIFIED");
 75             heightSize = heightSize <= mMaxHeight ? heightSize : (int)mMaxHeight;
 76         }
 77         if(heightMode == View.MeasureSpec.AT_MOST){
 78             Log.d("wang", "heightMode == View.MeasureSpec.AT_MOST");
 79             heightSize = heightSize <= mMaxHeight ? heightSize : (int)mMaxHeight;
 80         }
 81
 82         int maxHeightMeasureSpec = View.MeasureSpec.makeMeasureSpec(heightSize, heightMode);
 83
 84         super.onMeasure(widthMeasureSpec, maxHeightMeasureSpec);
 85     }
 86
 87
 88     /**
 89      * 获取屏幕高度
 90      * @param context
 91      */
 92     public static int getScreenHeight(Context context){
 93         WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
 94         return wm.getDefaultDisplay().getHeight();
 95     }
 96
 97     /**
 98      * 获取屏幕宽度
 99      * @param context
100      */
101     public static int getScreenWidth(Context context){
102         WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
103         return wm.getDefaultDisplay().getWidth();
104     }
105
106     /**
107      * 获取屏幕大小
108      * @param context
109      * @param outDimension
110      */
111     public static void getScreenDimension(Context context, int[] outDimension){
112         WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
113         outDimension[0] = wm.getDefaultDisplay().getWidth();
114         outDimension[1] = wm.getDefaultDisplay().getHeight();
115     }
116
117 }

属性文件如下：

attrs.xml

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <resources>
 3
 4     <declare-styleable name="maxHeightView">
 5         <attr name="maxHeightRatio" format="reference|float" />
 6         <attr name="maxHeightDimen" format="reference|dimension" />
 7     </declare-styleable>
 8
 9
10 </resources>

使用方法：

在布局中使用如下代码：

 1 <cn.carbs.maxheightview.MaxHeightView
 2         android:id="@+id/maxview"
 3         android:layout_width="match_parent"
 4         android:layout_height="wrap_content"
 5         app:maxHeightRatio="0.7" >
 6
 7         <ScrollView
 8             android:layout_width="match_parent"
 9             android:layout_height="wrap_content" >
10
11             <LinearLayout
12                 android:layout_width="match_parent"
13                 android:layout_height="wrap_content"
14                 android:orientation="vertical" >
15
16                 <Button
17                     android:id="@+id/button0"
18                     android:layout_width="match_parent"
19                     android:layout_height="60dp"
20                     android:text="button0" />
21               ...............
22
23             </LinearLayout>
24         </ScrollView>
25     </cn.carbs.maxheightview.MaxHeightView>

要注意，此自定义view继承自FrameLayout，使用时最好嵌套一个ScrollView，以提高用户体验