自定义View(一)，初识自定义View

看了无数资料，总结一下自定义View
先明白一个自定义View的三大流程

• onMeasure()
  测量,决定View的大小

• onLayout()
  布局,决定View在ViewGroup中的位置

• onDraw()
  绘制,画出这个View的内容

这三个方法都存在于View类中，我们自定义View需要针对这三个方法做出修改来达到我们需要的目标或功能
先来一个最基本的例子，我们单纯的画一个圆，我们只需修改onDraw()方法即可
MyCustomVew.java

1. public class MyCustomView extends View { 
   

   ---

2. ---

3. public MyCustomView(Context context, AttributeSet attrs, int defStyleAttr) { 
   

   ---

4. super(context, attrs, defStyleAttr); 
   

   ---

5. // TODO Auto-generated constructor stub 
   

   ---

6. } 
   

   ---

7. ---

8. public MyCustomView(Context context, AttributeSet attrs) { 
   

   ---

9. super(context, attrs); 
   

   ---

10. // TODO Auto-generated constructor stub 
    

    ---

11. } 
    

    ---

12. ---

13. public MyCustomView(Context context) { 
    

    ---

14. super(context); 
    

    ---

15. // TODO Auto-generated constructor stub 
    

    ---

16. } 
    

    ---

17. ---

18. @Override 
    

    ---

19. protected void onDraw(Canvas canvas) { 
    

    ---

20. // TODO Auto-generated method stub 
    

    ---

21. super.onDraw(canvas); 
    

    ---

22. // 实例化画笔并打开抗锯齿 
    

    ---

23. Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG); 
    

    ---

24. // 设置画笔颜色 
    

    ---

25. paint.setColor(Color.RED); 
    

    ---

26. /** 
    

    ---

27. * 画笔样式分三种：  
    

    ---

28. * 1.Paint.Style.STROKE：描边  
    

    ---

29. * 2.Paint.Style.FILL_AND_STROKE：描边并填充 
    

    ---

30. * 3.Paint.Style.FILL：填充 既然是画圆，那么就选择样式为描边 
    

    ---

31. */ 
    

    ---

32. paint.setStyle(Paint.Style.STROKE); 
    

    ---

33. /* 
    

    ---

34. * 设置描边的粗细，单位：像素px 注意：当setStrokeWidth(0)的时候描边宽度并不为0而是只占一个像素 
    

    ---

35. */ 
    

    ---

36. paint.setStrokeWidth(10); 
    

    ---

37. // 参数含义依次为：圆心X坐标、圆心Y坐标、圆半径、画笔 
    

    ---

38. canvas.drawCircle(500, 500, 200, paint); 
    

    ---

39. } 
    

    ---

40. } 
    

    ---

在Activity的布局文件中引入这个自定义View

1. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
   

   ---

2. xmlns:app="http://schemas.android.com/apk/res-auto" 
   

   ---

3. android:id="@+id/main_root_ll" 
   

   ---

4. android:layout_width="match_parent" 
   

   ---

5. android:layout_height="match_parent" 
   

   ---

6. android:orientation="vertical" > 
   

   ---

7. ---

8. <com.example.testcustomview.MyCustomView 
   

   ---

9. android:id="@+id/main_cv" 
   

   ---

10. android:layout_width="match_parent" 
    

    ---

11. android:layout_height="match_parent" /> 
    

    ---

12. ---

13. </LinearLayout> 
    

    ---

运行结果如下

如果我们想要让这个圆动起来呢？我们只要不断的去修改onDraw()不断的绘制就可以了
譬如我们想要画一个由小到大的实心圆，我们需要做的就是不断的改变的半径
MyCustomView

1. public class MyCustomView extends View implements Runnable { 
   

   ---

2. ---

3. private int radiu;// 圆的半径 
   

   ---

4. private Paint paint; 
   

   ---

5. ---

6. public MyCustomView(Context context, AttributeSet attrs) { 
   

   ---

7. super(context, attrs); 
   

   ---

8. initPaint(); 
   

   ---

9. } 
   

   ---

10. ---

11. public MyCustomView(Context context) { 
    

    ---

12. this(context, null); 
    

    ---

13. } 
    

    ---

14. ---

15. public void initPaint() { 
    

    ---

16. paint = new Paint(Paint.ANTI_ALIAS_FLAG); 
    

    ---

17. // 设置画笔颜色 
    

    ---

18. paint.setColor(Color.RED); 
    

    ---

19. /** 
    

    ---

20. * 画笔样式分三种： 1.Paint.Style.STROKE：描边 2.Paint.Style.FILL_AND_STROKE：描边并填充 
    

    ---

21. * 3.Paint.Style.FILL：填充 既然是画圆，那么就选择样式为描边 
    

    ---

22. */ 
    

    ---

23. paint.setStyle(Paint.Style.FILL_AND_STROKE); 
    

    ---

24. /* 
    

    ---

25. * 设置描边的粗细，单位：像素px 注意：当setStrokeWidth(0)的时候描边宽度并不为0而是只占一个像素 
    

    ---

26. */ 
    

    ---

27. paint.setStrokeWidth(10); 
    

    ---

28. } 
    

    ---

29. ---

30. @Override 
    

    ---

31. protected void onDraw(Canvas canvas) { 
    

    ---

32. // TODO Auto-generated method stub 
    

    ---

33. super.onDraw(canvas); 
    

    ---

34. canvas.drawCircle(500, 500, radiu, paint); 
    

    ---

35. } 
    

    ---

36. ---

37. @Override 
    

    ---

38. public void run() { 
    

    ---

39. while (radiu <= 200) { 
    

    ---

40. try { 
    

    ---

41. radiu += 10; 
    

    ---

42. Thread.sleep(300); 
    

    ---

43. //刷新View 
    

    ---

44. postInvalidate(); 
    

    ---

45. } catch (InterruptedException e) { 
    

    ---

46. // TODO Auto-generated catch block 
    

    ---

47. e.printStackTrace(); 
    

    ---

48. } 
    

    ---

49. } 
    

    ---

50. } 
    

    ---

51. } 
    

    ---

可以看到我们在run方法中调用了一个postInvalidate()，这个方法还有一个对应的方法Invalidate(),这两个方法的区别在于

• postInvalidate()
  前者是在非UI线程中使,用来刷新界面

• Invalidate()
  在UI线程自身中使用,用来刷新界面

刚才的例子是画了一个圆，canvas还提供了其他一系列方法来供我们调用，用来画各种各样的图形
下篇文章来介绍