自定义View的时候经常少不了获取View的宽高信息,当然不一定是自定义View的时候才会需要获取宽高信息,其他情况下我们也会有这样的需求,获取方式和获取的时机也十分讲究.下面分别从这几个api讲起:
1.构造方法
2.onFinishInflate
3.onSizeChanged
4.onMeasure
5.onWindowFocusChanged
6.onLayout
7.View.getViewTreeObserver().addOnGlobalLayoutListener
以上几种方式获取的时机各有不同,且回调次数和条件也不相同.先来看看demo,下面是一个自定义的FrameLayout的子类,包含2个TextView控件.
布局如下:
[html]
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1. <?xml version="1.0" encoding="utf-8"?>
2. <mchenys.net.csdn.blog.testlayout.view.TestLayout
3. xmlns:android="http://schemas.android.com/apk/res/android"
4. xmlns:tools="http://schemas.android.com/tools"
5. android:layout_width="match_parent"
6. android:layout_height="match_parent"
7. >
8. <TextView
9. android:layout_width="match_parent"
10. android:layout_height="300dp"
11. android:background="#f00"
12. android:gravity="center"
13. android:text="First Part"
14. android:textSize="30sp"/>
15.
16. <TextView
17. android:layout_width="match_parent"
18. android:layout_height="match_parent"
19. android:layout_marginTop="300dp"
20. android:background="#00f"
21. android:gravity="center"
22. android:text="Second Part"
23. android:textSize="30sp"/>
24. </mchenys.net.csdn.blog.testlayout.view.TestLayout>
代码:
[java]
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1. /**
2. * Created by mChenys on 2015/12/23.
3. */
4. public class TestLayout extends FrameLayout {
5. private View mFistPart, mSecondPart;
6. private int mFistHeight, mSecondHeight;
7.
8. public TestLayout(Context context) {
9. this(context, null);
10. }
11.
12. public TestLayout(Context context, AttributeSet attrs) {
13. this(context, attrs, 0);
14. }
15.
16. public TestLayout(Context context, AttributeSet attrs, int defStyleAttr) {
17. super(context, attrs, defStyleAttr);
18. "----------Constructor-------------");
19. 0);
20. 1);
21. "mFistPart:" + mFistPart + " mSecondPart:" + mSecondPart);
22. }
23.
24. @Override
25. protected void onFinishInflate() {
26. super.onFinishInflate();
27. 0);
28. 1);
29. mFistHeight = mFistPart.getMeasuredHeight();
30. mSecondHeight = mSecondPart.getMeasuredHeight();
31. "----------onFinishInflate-------------");
32. "mFistPart:" + mFistPart + " mSecondPart:" + mSecondPart);
33. "mFistPart.getMeasuredHeight():" + mFistHeight + " mSecondPart.getMeasuredHeight():" + mSecondHeight);
34. "mFistPart.getHeight():" + mFistPart.getHeight() + " mSecondPart.getHeight():" + mSecondPart.getHeight());
35. new ViewTreeObserver.OnGlobalLayoutListener() {
36. @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
37. @Override
38. public void onGlobalLayout() {
39. "----------addOnGlobalLayoutListener-------------");
40. this);
41. "mFistPart.getMeasuredHeight():" + mFistPart.getMeasuredHeight() + "mFistPart.getHeight():" + mFistPart.getMeasuredHeight());
42. }
43. });
44. new ViewTreeObserver.OnGlobalLayoutListener() {
45. @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
46. @Override
47. public void onGlobalLayout() {
48. "----------addOnGlobalLayoutListener-------------");
49. this);
50. "mFistPart.getMeasuredHeight():" + mSecondPart.getMeasuredHeight() + "mFistPart.getHeight():" + mSecondPart.getMeasuredHeight());
51. }
52. });
53. }
54.
55. @Override
56. protected void onSizeChanged(int w, int h, int oldw, int oldh) {
57. super.onSizeChanged(w, h, oldw, oldh);
58. mFistHeight = mFistPart.getMeasuredHeight();
59. mSecondHeight = mSecondPart.getMeasuredHeight();
60. "----------onSizeChanged-------------");
61. "mFistPart:" + mFistPart + " mSecondPart:" + mSecondPart);
62. "mFistPart.getMeasuredHeight():" + mFistHeight + " mSecondPart.getMeasuredHeight():" + mSecondHeight);
63. "mFistPart.getHeight():" + mFistPart.getHeight() + " mSecondPart.getHeight():" + mSecondPart.getHeight());
64. }
65.
66. @Override
67. protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
68. super.onMeasure(widthMeasureSpec, heightMeasureSpec);
69. mFistHeight = mFistPart.getMeasuredHeight();
70. mSecondHeight = mSecondPart.getMeasuredHeight();
71. "----------onMeasure-------------");
72. "mFistPart:" + mFistPart + " mSecondPart:" + mSecondPart);
73. "mFistPart.getMeasuredHeight():" + mFistHeight + " mSecondPart.getMeasuredHeight():" + mSecondHeight);
74. "mFistPart.getHeight():" + mFistPart.getHeight() + " mSecondPart.getHeight():" + mSecondPart.getHeight());
75. }
76.
77. @Override
78. public void onWindowFocusChanged(boolean hasWindowFocus) {
79. super.onWindowFocusChanged(hasWindowFocus);
80. mFistHeight = mFistPart.getMeasuredHeight();
81. mSecondHeight = mSecondPart.getMeasuredHeight();
82. "----------onWindowFocusChanged-------------");
83. "mFistPart:" + mFistPart + " mSecondPart:" + mSecondPart + " hasWindowFocus:" + hasWindowFocus);
84. "mFistPart.getMeasuredHeight():" + mFistHeight + " mSecondPart.getMeasuredHeight():" + mSecondHeight);
85. "mFistPart.getHeight():" + mFistPart.getHeight() + " mSecondPart.getHeight():" + mSecondPart.getHeight());
86. }
87.
88. @Override
89. protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
90. super.onLayout(changed, left, top, right, bottom);
91. mFistHeight = mFistPart.getMeasuredHeight();
92. mSecondHeight = mSecondPart.getMeasuredHeight();
93. "----------onLayout-------------");
94. "mFistPart:" + mFistPart + " mSecondPart:" + mSecondPart);
95. "mFistPart.getMeasuredHeight():" + mFistHeight + " mSecondPart.getMeasuredHeight():" + mSecondHeight);
96. "mFistPart.getHeight():" + mFistPart.getHeight() + " mSecondPart.getHeight():" + mSecondPart.getHeight());
97. }
98. }
上面每一种方法都分别打印了该自定义控件的2个子控件引用,2个子控件的getMeasuredHeight和2个子控件的getHeight,来看下log:
[html]
view plain
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1. System.out: ----------Constructor-------------
2. System.out: mFistPart:null mSecondPart:null
3. System.out: ----------onFinishInflate-------------
4. System.out: mFistPart:android.support.v7.widget.AppCompatTextView{fb4034c V.ED..... ......ID 0,0-0,0} mSecondPart:android.support.v7.widget.AppCompatTextView{16ebf95 V.ED..... ......ID 0,0-0,0}
5. System.out: mFistPart.getMeasuredHeight():0 mSecondPart.getMeasuredHeight():0
6. System.out: mFistPart.getHeight():0 mSecondPart.getHeight():0
7. System.out: ----------onMeasure-------------
8. System.out: mFistPart:android.support.v7.widget.AppCompatTextView{fb4034c V.ED..... ......ID 0,0-0,0} mSecondPart:android.support.v7.widget.AppCompatTextView{16ebf95 V.ED..... ......ID 0,0-0,0}
9. System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():328
10. System.out: mFistPart.getHeight():0 mSecondPart.getHeight():0
11.
12. System.out: ----------onMeasure-------------
13. System.out: mFistPart:android.support.v7.widget.AppCompatTextView{fb4034c V.ED..... ......ID 0,0-0,0} mSecondPart:android.support.v7.widget.AppCompatTextView{16ebf95 V.ED..... ......ID 0,0-0,0}
14. System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424
15. System.out: mFistPart.getHeight():0 mSecondPart.getHeight():0
16. System.out: ----------onSizeChanged-------------
17. System.out: mFistPart:android.support.v7.widget.AppCompatTextView{fb4034c V.ED..... ......ID 0,0-0,0} mSecondPart:android.support.v7.widget.AppCompatTextView{16ebf95 V.ED..... ......ID 0,0-0,0}
18. System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424
19. System.out: mFistPart.getHeight():0 mSecondPart.getHeight():0
20. System.out: ----------onLayout-------------
21. System.out: mFistPart:android.support.v7.widget.AppCompatTextView{fb4034c V.ED..... ......ID 0,0-720,600} mSecondPart:android.support.v7.widget.AppCompatTextView{16ebf95 V.ED..... ......ID 0,600-720,1024}
22. System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424
23. System.out: mFistPart.getHeight():600 mSecondPart.getHeight():424
24. System.out: ----------addOnGlobalLayoutListener-------------
25. System.out: mFistPart.getMeasuredHeight():600mFistPart.getHeight():600
26. System.out: ----------addOnGlobalLayoutListener-------------
27. System.out: mFistPart.getMeasuredHeight():424mFistPart.getHeight():424
28. System.out: ----------onWindowFocusChanged-------------
29. System.out: mFistPart:android.support.v7.widget.AppCompatTextView{fb4034c V.ED..... ......ID 0,0-720,600} mSecondPart:android.support.v7.widget.AppCompatTextView{16ebf95 V.ED..... ......ID 0,600-720,1024} hasWindowFocus:true
30. System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424
31. System.out: mFistPart.getHeight():600 mSecondPart.getHeight():424
32. System.out: ----------onMeasure-------------
33. System.out: mFistPart:android.support.v7.widget.AppCompatTextView{fb4034c V.ED..... ......ID 0,0-720,600} mSecondPart:android.support.v7.widget.AppCompatTextView{16ebf95 V.ED..... ......ID 0,600-720,1024}
34. System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424
35. System.out: mFistPart.getHeight():600 mSecondPart.getHeight():424
36. System.out: ----------onLayout-------------
37. System.out: mFistPart:android.support.v7.widget.AppCompatTextView{fb4034c V.ED..... ......ID 0,0-720,600} mSecondPart:android.support.v7.widget.AppCompatTextView{16ebf95 V.ED..... ......ID 0,600-720,1024}
38. System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424
39. System.out: mFistPart.getHeight():600 mSecondPart.getHeight():424
总结:
1.从执行顺序分析
Constructor->onFinishInflate->onMeasure..->onSizeChanged->onLayout->addOnGlobalLayoutListener->onWindowFocusChanged->onMeasure->onLayout
由上可知,onMeasure和onLayout会被多次调用.
2.从api上分析
1)Constructor:构造方法,View初始化的时候调用,在这里是无法获取其子控件的引用的.更加无法获取宽高了.
2)onFinishInflate:当布局初始化完毕后回调,在这里可以获取所有直接子View的引用,但是无法获取宽高.
3)onMeasure:当测量控件宽高时回调,当调用了requestLayout()也会回调onMeasure.在这里一定可以通过getMeasuredHeight()和getMeasuredWidth()来获取控件的高和宽,但不一定可以通过getHeight()和getWidth()来获取控件宽高,因为getHeight()和getWidth()必须要等onLayout方法回调之后才能确定.
4)onSizeChanged:当控件的宽高发生变化时回调,和onMeasure一样,一定可以通过getMeasuredHeight()和getMeasuredWidth()来获取控件的高和宽,因为它是在onMeasure方法执行之后和onLayout方法之前回调的.
5)onLayout:当确定控件的位置时回调,当调用了requestLayout()也会回调onLayout.在这里一定可以通过getHeight()和getWidth()获取控件的宽高,同时由于onMeasure方法比onLayout方法先执行,所以在这里也可以通过getMeasuredHeight()和getMeasuredWidth()来获取控件的高和宽.
6)addOnGlobalLayoutListener:当View的位置确定完后会回调改监听方法,它是紧接着onLayout方法执行而执行的,只要onLayout方法调用了,那么addOnGlobalLayoutListener的监听器就会监听到.在这里getMeasuredHeight()和getMeasuredWidth()和getHeight()和getWidth()都可以获取到宽高.
7)onWindowFocusChanged:当View的焦点发送改变时回调,在这里getMeasuredHeight()和getMeasuredWidth()和getHeight()和getWidth()都可以获取到宽高.Activity也可以通过重写该方法来判断当前的焦点是否发送改变了;需要注意的是这里View获取焦点和失去焦点都会回调.
那么,上面分析了那么多方法来获取控件的宽高,那到底用哪一种呢?
具体要用哪一种,是需要根据View的宽高是否会发生变化来决定:
1.如果自定义的View在使用的过程中宽高信息是不会改变的,那么上面方式3~方式7都可以使用.
2.如果自定义的View在使用过程中宽高信息都会发生改变的,而且又需要获取一开始时的宽高信息,那么建议使用View.getViewTreeObserver().addOnGlobalLayoutListener(OnGlobalLayoutListener listener)的方式,因为这种方式有getViewTreeObserver().removeOnGlobalLayoutListener(this);来避免回调函数因宽高信息的变化而多次调用,如果使用其他方式的话,就要借助额外的变量来保证获取到的宽高是View的初始高度.
