Android 自定义view 和 onMeasure方法介绍

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http://blog.csdn.net/gf771115/article/details/9730439

http://blog.csdn.net/gf771115/article/details/9730439

http://blog.csdn.net/gf771115/article/details/9730439

http://blog.csdn.net/gf771115/article/details/9730439

http://blog.csdn.net/gf771115/article/details/9730439

http://blog.csdn.net/gf771115/article/details/9730439

Android 自定义view 和 onMeasure方法介绍

分类： Android/OMS 2013-08-03 10:47  616人阅读  评论(0)  收藏  举报

转自：http://blog.csdn.net/cyq1028/article/details/7390631

http://blog.csdn.net/sunny2come/article/details/7287298

哈哈，兄弟我终于自己写了一个view，不是网上那种简单的哦，还是有一定技术含量的，

我是通过学习ApiDemo（android自带的sample）里面LabelView实现的，

先谈谈学习过程，觉得一开始不应当盲目的动手做，应对想把原理搞明白，哪怕一个很小的View，也应当将各个细节弄清楚，

等这些搞定了，接下来的工作就是水道渠成了！

自定义一个View那必须继承View，

首先说说我的View是啥，恩，很简单，就是一个椭圆，其中可以设置4个参数，分别是top、left、right、bottom，应该很清楚吧，因为canvas.drawOval时用到了4个值，

首先得定义4个属性值，是我的View专有的，

建立attr.xml放到values下面

 <?xml version="1.0" encoding="UTF-8"?>
 <resources>
 <declare-styleable name="RocketView">
 <attr name="ovalLeft" format="dimension" />
 <attr name="ovalTop" format="dimension" />
 <attr name="ovalRight" format="dimension" />
 <attr name="ovalBottom" format="dimension" />
 </declare-styleable>
 </resources>

 <?xml version="1.0" encoding="UTF-8"?>
 <resources>
      <declare-styleable name="RocketView">
         <attr name="ovalLeft" format="dimension" />
         <attr name="ovalTop" format="dimension" />
         <attr name="ovalRight" format="dimension" />
         <attr name="ovalBottom" format="dimension" />
     </declare-styleable>
 </resources>

然后写个RocketView

 package com.myos;

 import android.content.Context;
 import android.content.res.TypedArray;
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.graphics.Paint;
 import android.graphics.RectF;
 import android.util.AttributeSet;
 import android.util.Log;
 import android.view.View;
 import android.view.View.MeasureSpec;

 public class RocketView extends View{
 private Paint mOvalPaint;
 private int mStrokeWidth = 2;
 private int padding = 3;

 //椭圆参数
 private int mOval_l;
 private int mOval_t;
 private int mOval_r;
 private int mOval_b;



 //构造
 public RocketView(Context context, AttributeSet attrs) {
 super(context, attrs);
 initRocketView();

 TypedArray a = context.obtainStyledAttributes(attrs,
 R.styleable.RocketView);

 mOval_l = a.getDimensionPixelOffset(R.styleable.RocketView_ovalLeft, padding);
 mOval_t = a.getDimensionPixelOffset(R.styleable.RocketView_ovalTop, padding);
 mOval_r = a.getDimensionPixelOffset(R.styleable.RocketView_ovalRight, 100);
 mOval_b = a.getDimensionPixelOffset(R.styleable.RocketView_ovalBottom, 100);

 a.recycle();
 }

 private void initRocketView() {
 mOvalPaint = new Paint();
 mOvalPaint.setAntiAlias(true);
 mOvalPaint.setColor(Color.BLUE);
 mOvalPaint.setStyle(Paint.Style.STROKE);
 mOvalPaint.setStrokeWidth(mStrokeWidth);
 setPadding(padding,padding,padding,padding);
 }

 public void setOvalRect(int l, int t, int r, int b){
 mOval_l = l + padding;
 mOval_t = t + padding;
 mOval_r = r;
 mOval_b = b;
 requestLayout();
 invalidate();
 }
 @Override
 protected void onDraw(Canvas canvas) {
 // TODO Auto-generated method stub
 super.onDraw(canvas);
 canvas.drawColor(Color.WHITE);
 // 绘制椭圆
 RectF re11 = new RectF(mOval_l, mOval_t, mOval_r, mOval_b);
 canvas.drawOval(re11, mOvalPaint);

 // // 绘制圆形
 // canvas.drawCircle(mCircle_x, mCircle_y, mCircle_r, mPaint);
 }

 /**
 * @see android.view.View#measure(int, int)
 */
 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
 setMeasuredDimension(measureWidth(widthMeasureSpec),
 measureHeight(heightMeasureSpec));
 }

 /**
 * Determines the width of this view
 * @param measureSpec A measureSpec packed into an int
 * @return The width of the view, honoring constraints from measureSpec
 */
 private int measureWidth(int measureSpec) {
 int result = 0;
 int specMode = MeasureSpec.getMode(measureSpec);
 int specSize = MeasureSpec.getSize(measureSpec);

 if (specMode == MeasureSpec.EXACTLY) {
 // We were told how big to be
 result = specSize;
 } else {
 // Measure the text
 result = mOval_r + getPaddingLeft()
 + getPaddingRight();
 if (specMode == MeasureSpec.AT_MOST) {
 // Respect AT_MOST value if that was what is called for by measureSpec
 result = Math.min(result, specSize);
 }
 }

 return result;
 }

 /**
 * Determines the height of this view
 * @param measureSpec A measureSpec packed into an int
 * @return The height of the view, honoring constraints from measureSpec
 */
 private int measureHeight(int measureSpec) {
 int result = 0;
 int specMode = MeasureSpec.getMode(measureSpec);
 int specSize = MeasureSpec.getSize(measureSpec);

 if (specMode == MeasureSpec.EXACTLY) {
 // We were told how big to be
 result = specSize;
 } else {
 // Measure the text (beware: ascent is a negative number)
 result = mOval_b + getPaddingTop()
 + getPaddingBottom();
 if (specMode == MeasureSpec.AT_MOST) {
 // Respect AT_MOST value if that was what is called for by measureSpec
 result = Math.min(result, specSize);
 }
 }

 return result;
 }
 }

 package com.myos;

 import android.content.Context;
 import android.content.res.TypedArray;
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.graphics.Paint;
 import android.graphics.RectF;
 import android.util.AttributeSet;
 import android.util.Log;
 import android.view.View;
 import android.view.View.MeasureSpec;

 public class RocketView extends View{
     private Paint mOvalPaint;
     private int mStrokeWidth = 2;
     private int padding = 3;

     //椭圆参数
     private int mOval_l;
     private int mOval_t;
     private int mOval_r;
     private int mOval_b;



     //构造
     public RocketView(Context context, AttributeSet attrs) {
         super(context, attrs);
         initRocketView();

         TypedArray a = context.obtainStyledAttributes(attrs,
                 R.styleable.RocketView);

         mOval_l = a.getDimensionPixelOffset(R.styleable.RocketView_ovalLeft, padding);
         mOval_t = a.getDimensionPixelOffset(R.styleable.RocketView_ovalTop, padding);
         mOval_r = a.getDimensionPixelOffset(R.styleable.RocketView_ovalRight, 100);
         mOval_b = a.getDimensionPixelOffset(R.styleable.RocketView_ovalBottom, 100);

         a.recycle();
     }

     private void initRocketView() {
         mOvalPaint = new Paint();
         mOvalPaint.setAntiAlias(true);
         mOvalPaint.setColor(Color.BLUE);
         mOvalPaint.setStyle(Paint.Style.STROKE);
         mOvalPaint.setStrokeWidth(mStrokeWidth);
         setPadding(padding,padding,padding,padding);
     }

     public void setOvalRect(int l, int t, int r, int b){
         mOval_l = l + padding;
         mOval_t = t + padding;
         mOval_r = r;
         mOval_b = b;
         requestLayout();
         invalidate();
     }
     @Override
     protected void onDraw(Canvas canvas) {
         // TODO Auto-generated method stub
         super.onDraw(canvas);
         canvas.drawColor(Color.WHITE);
         // 绘制椭圆
         RectF re11 = new RectF(mOval_l, mOval_t, mOval_r, mOval_b);
         canvas.drawOval(re11, mOvalPaint);

 //      // 绘制圆形
 //      canvas.drawCircle(mCircle_x, mCircle_y, mCircle_r, mPaint);
     }

      /**
       * @see android.view.View#measure(int, int)
       */
      @Override
      protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
          setMeasuredDimension(measureWidth(widthMeasureSpec),
                  measureHeight(heightMeasureSpec));
      }

      /**
       * Determines the width of this view
       * @param measureSpec A measureSpec packed into an int
       * @return The width of the view, honoring constraints from measureSpec
       */
      private int measureWidth(int measureSpec) {
          int result = 0;
          int specMode = MeasureSpec.getMode(measureSpec);
          int specSize = MeasureSpec.getSize(measureSpec);

          if (specMode == MeasureSpec.EXACTLY) {
              // We were told how big to be
              result = specSize;
          } else {
              // Measure the text
              result = mOval_r + getPaddingLeft()
                      + getPaddingRight();
              if (specMode == MeasureSpec.AT_MOST) {
                  // Respect AT_MOST value if that was what is called for by measureSpec
                  result = Math.min(result, specSize);
              }
          }

          return result;
      }

      /**
       * Determines the height of this view
       * @param measureSpec A measureSpec packed into an int
       * @return The height of the view, honoring constraints from measureSpec
       */
      private int measureHeight(int measureSpec) {
          int result = 0;
          int specMode = MeasureSpec.getMode(measureSpec);
          int specSize = MeasureSpec.getSize(measureSpec);

          if (specMode == MeasureSpec.EXACTLY) {
              // We were told how big to be
              result = specSize;
          } else {
              // Measure the text (beware: ascent is a negative number)
              result = mOval_b + getPaddingTop()
                      + getPaddingBottom();
              if (specMode == MeasureSpec.AT_MOST) {
                  // Respect AT_MOST value if that was what is called for by measureSpec
                  result = Math.min(result, specSize);
              }
          }

          return result;
      }
 }

在构造中getDimensionPixelOffset检索出一个属性值，没有的话就使用第2个参数做默认值，

可以在布局xml中初始化这个属性值，下面是我main.xml

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:app="http://schemas.android.com/apk/res/com.myos"
 android:orientation="vertical"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent"
 >

 <TextView
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="@string/hello"
 />

 <com.myos.RocketView
 app:ovalLeft="0dp"
 android:id="@+id/rv"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content" />


 </LinearLayout>

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res/com.myos"
     android:orientation="vertical"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
     >

     <TextView
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:text="@string/hello"
         />

     <com.myos.RocketView
         app:ovalLeft="0dp"
         android:id="@+id/rv"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content" />


 </LinearLayout>

我这里没啥用处，仅仅试一下，待扩展属性时再说，说明一下xmlns:app中app可以随便命名的，这个android的规矩还真多

另外构造函数中onMeasure很重要的，onDraw很明显就是画椭圆了，android在画的时候呢，会去先测量，需要我们来提供View的宽和高，

大家都知道wrap_content、fill_parent，测量时会有3种模式，分别是UNSPECIFIED、EXACTLY、AT_MOST，

当使用

wrap_content时就是AT_MOST模式，fill_parent就是EXACTLY模式，可以看看官方文档：

http://developer.android.com/guide/topics/ui/how-android-draws.html

相信研读一下代码就明白了

RocketView定义好了，接下来就是使用了

 package com.myos;

 import android.app.Activity;
 import android.os.Bundle;

 public class MainActivity extends Activity {
 RocketView mRocketView;
 /** Called when the activity is first created. */
 @Override
 public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.main);

 mRocketView = (RocketView)findViewById(R.id.rv);
 mRocketView.setOvalRect(0, 0, 500, 100);
 }
 }

 package com.myos;

 import android.app.Activity;
 import android.os.Bundle;

 public class MainActivity extends Activity {
     RocketView mRocketView;
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.main);

         mRocketView = (RocketView)findViewById(R.id.rv);
         mRocketView.setOvalRect(0, 0, 500, 100);
     }
 }

可以通过setOvalRect函数来动态调整椭圆的大小！

下面是运行效果，ko啦！

onMeasure方法在控件的父元素正要放置它的子控件时调用.它会问一个问题，“你想要用多大地方啊？”，然后传入两个参数——widthMeasureSpec和heightMeasureSpec.

　　它们指明控件可获得的空间以及关于这个空间描述的元数据.
　　比返回一个结果要好的方法是你传递View的高度和宽度到setMeasuredDimension方法里.
(请发邮件到 [email protected] 获得翻强软件，能上youtube哟。)
　　接下来的代码片段给出了如何重写onMeasure.注意，调用的本地空方法是来计算高度和宽度的.它们会译解widthHeightSpec和heightMeasureSpec值，并计算出合适的高度和宽度值.

java代码：

1. @Override
   
2. protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
   
3. 
   
4. int measuredHeight = measureHeight(heightMeasureSpec);
   
5. int measuredWidth = measureWidth(widthMeasureSpec);
   
6. setMeasuredDimension(measuredHeight, measuredWidth);
   
7. }
   
8. 
   
9. private int measureHeight(int measureSpec) {
   
10. 
    
11. 
    
12. // Return measured widget height.
    
13. }
    
14. 
    
15. private int measureWidth(int measureSpec) {
    
16. 
    
17. // Return measured widget width.
    
18. }

复制代码

边界参数——widthMeasureSpec和heightMeasureSpec ，效率的原因以整数的方式传入。

MeasureSpec封装了父布局传递给子布局的布局要求，每个MeasureSpec代表了一组宽度和高度的要求。一个MeasureSpec由大小和模式组成。

它有三种模式：

UNSPECIFIED(未指定), 父元素不对自元素施加任何束缚，子元素可以得到任意想要的大小；

EXACTLY(完全)，父元素决定自元素的确切大小，子元素将被限定在给定的边界里而忽略它本身大小；

AT_MOST(至多)，子元素至多达到指定大小的值。

它常用的三个函数：

　　 1.static int getMode(int measureSpec):根据提供的测量值(格式)提取模式(上述三个模式之一)

　　2.static int getSize(int measureSpec):根据提供的测量值(格式)提取大小值(这个大小也就是我们通常所说的大小)

　　3.static int makeMeasureSpec(int size,int mode):根据提供的大小值和模式创建一个测量值(格式)

这个类的使用呢，通常在view组件的onMeasure方法里面调用但也有少数例外

在它们使用之前，首先要做的是使用MeasureSpec类的静态方法getMode和getSize来译解，如下面的片段所示：

java代码：

1. int specMode = MeasureSpec.getMode(measureSpec);
   
2. int specSize = MeasureSpec.getSize(measureSpec);

复制代码

依据specMode的值，如果是AT_MOST，specSize 代表的是最大可获得的空间；如果是EXACTLY，specSize 代表的是精确的尺寸；如果是UNSPECIFIED，对于控件尺寸来说，没有任何参考意义。
　　当以EXACT方式标记测量尺寸，父元素会坚持在一个指定的精确尺寸区域放置View。在父元素问子元素要多大空间时，AT_MOST指示者会说给我最大的范围。在很多情况下，你得到的值都是相同的。
　　在两种情况下，你必须绝对的处理这些限制。在一些情况下，它可能会返回超出这些限制的尺寸，在这种情况下，你可以让父元素选择如何对待超出的View，使用裁剪还是滚动等技术。

　　接下来的框架代码给出了处理View测量的典型实现：

java代码：

1. @Override
   
2. 
   
3. protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
   
4. 
   
5. int measuredHeight = measureHeight(heightMeasureSpec);
   
6. 
   
7. int measuredWidth = measureWidth(widthMeasureSpec);
   
8. 
   
9. setMeasuredDimension(measuredHeight, measuredWidth);
   
10. 
    
11. }
    
12. 
    
13. private int measureHeight(int measureSpec) {
    
14. 
    
15. int specMode = MeasureSpec.getMode(measureSpec);
    
16. int specSize = MeasureSpec.getSize(measureSpec);
    
17. 
    
18. // Default size if no limits are specified.
    
19. 
    
20. int result = 500;
    
21. if (specMode == MeasureSpec.AT_MOST){
    
22. 
    
23. // Calculate the ideal size of your
    
24. // control within this maximum size.
    
25. // If your control fills the available
    
26. // space return the outer bound.
    
27. 
    
28. result = specSize;
    
29. } 
    
30. else if (specMode == MeasureSpec.EXACTLY){
    
31. 
    
32. // If your control can fit within these bounds return that value.
    
33. result = specSize;
    
34. }
    
35. 
    
36. return result;
    
37. }
    
38. 
    
39. private int measureWidth(int measureSpec) {
    
40. int specMode = MeasureSpec.getMode(measureSpec);
    
41. int specSize = MeasureSpec.getSize(measureSpec);
    
42. 
    
43. // Default size if no limits are specified.
    
44. int result = 500;
    
45. if (specMode == MeasureSpec.AT_MOST){
    
46. // Calculate the ideal size of your control
    
47. // within this maximum size.
    
48. // If your control fills the available space
    
49. // return the outer bound.
    
50. result = specSize;
    
51. } 
    
52. 
    
53. else if (specMode == MeasureSpec.EXACTLY){
    
54. // If your control can fit within these bounds return that value.
    
55. 
    
56. result = specSize;
    
57. }
    
58. 
    
59. return result;
    
60. }