浅谈自定义View的宽高获取

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:

<?xml version="1.0" encoding="utf-8"?><mchenys.net.csdn.blog.testlayout.view.TestLayout    xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    >    <TextView        android:layout_width="match_parent"        android:layout_height="300dp"        android:background="#f00"        android:gravity="center"        android:text="First Part"        android:textSize="30sp"/>    <TextView        android:layout_width="match_parent"        android:layout_height="match_parent"        android:layout_marginTop="300dp"        android:background="#00f"        android:gravity="center"        android:text="Second Part"        android:textSize="30sp"/></mchenys.net.csdn.blog.testlayout.view.TestLayout>

代码:

/** * Created by mChenys on 2015/12/23. */public class TestLayout extends FrameLayout {    private View mFistPart, mSecondPart;    private int mFistHeight, mSecondHeight;    public TestLayout(Context context) {        this(context, null);    }    public TestLayout(Context context, AttributeSet attrs) {        this(context, attrs, 0);    }    public TestLayout(Context context, AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);        System.out.println("----------Constructor-------------");        mFistPart = getChildAt(0);        mSecondPart = getChildAt(1);        System.out.println("mFistPart:" + mFistPart + " mSecondPart:" + mSecondPart);    }    @Override    protected void onFinishInflate() {        super.onFinishInflate();        mFistPart = getChildAt(0);        mSecondPart = getChildAt(1);        mFistHeight = mFistPart.getMeasuredHeight();        mSecondHeight = mSecondPart.getMeasuredHeight();        System.out.println("----------onFinishInflate-------------");        System.out.println("mFistPart:" + mFistPart + " mSecondPart:" + mSecondPart);        System.out.println("mFistPart.getMeasuredHeight():" + mFistHeight + " mSecondPart.getMeasuredHeight():" + mSecondHeight);        System.out.println("mFistPart.getHeight():" + mFistPart.getHeight() + " mSecondPart.getHeight():" + mSecondPart.getHeight());        mFistPart.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {            @TargetApi(Build.VERSION_CODES.JELLY_BEAN)            @Override            public void onGlobalLayout() {                System.out.println("----------addOnGlobalLayoutListener-------------");                mFistPart.getViewTreeObserver().removeOnGlobalLayoutListener(this);                System.out.println("mFistPart.getMeasuredHeight():" + mFistPart.getMeasuredHeight() + "mFistPart.getHeight():" + mFistPart.getMeasuredHeight());            }        });        mSecondPart.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {            @TargetApi(Build.VERSION_CODES.JELLY_BEAN)            @Override            public void onGlobalLayout() {                System.out.println("----------addOnGlobalLayoutListener-------------");                mSecondPart.getViewTreeObserver().removeOnGlobalLayoutListener(this);                System.out.println("mFistPart.getMeasuredHeight():" + mSecondPart.getMeasuredHeight() + "mFistPart.getHeight():" + mSecondPart.getMeasuredHeight());            }        });    }    @Override    protected void onSizeChanged(int w, int h, int oldw, int oldh) {        super.onSizeChanged(w, h, oldw, oldh);        mFistHeight = mFistPart.getMeasuredHeight();        mSecondHeight = mSecondPart.getMeasuredHeight();        System.out.println("----------onSizeChanged-------------");        System.out.println("mFistPart:" + mFistPart + " mSecondPart:" + mSecondPart);        System.out.println("mFistPart.getMeasuredHeight():" + mFistHeight + " mSecondPart.getMeasuredHeight():" + mSecondHeight);        System.out.println("mFistPart.getHeight():" + mFistPart.getHeight() + " mSecondPart.getHeight():" + mSecondPart.getHeight());    }    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        super.onMeasure(widthMeasureSpec, heightMeasureSpec);        mFistHeight = mFistPart.getMeasuredHeight();        mSecondHeight = mSecondPart.getMeasuredHeight();        System.out.println("----------onMeasure-------------");        System.out.println("mFistPart:" + mFistPart + " mSecondPart:" + mSecondPart);        System.out.println("mFistPart.getMeasuredHeight():" + mFistHeight + " mSecondPart.getMeasuredHeight():" + mSecondHeight);        System.out.println("mFistPart.getHeight():" + mFistPart.getHeight() + " mSecondPart.getHeight():" + mSecondPart.getHeight());    }    @Override    public void onWindowFocusChanged(boolean hasWindowFocus) {        super.onWindowFocusChanged(hasWindowFocus);        mFistHeight = mFistPart.getMeasuredHeight();        mSecondHeight = mSecondPart.getMeasuredHeight();        System.out.println("----------onWindowFocusChanged-------------");        System.out.println("mFistPart:" + mFistPart + " mSecondPart:" + mSecondPart + " hasWindowFocus:" + hasWindowFocus);        System.out.println("mFistPart.getMeasuredHeight():" + mFistHeight + " mSecondPart.getMeasuredHeight():" + mSecondHeight);        System.out.println("mFistPart.getHeight():" + mFistPart.getHeight() + " mSecondPart.getHeight():" + mSecondPart.getHeight());    }    @Override    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {        super.onLayout(changed, left, top, right, bottom);        mFistHeight = mFistPart.getMeasuredHeight();        mSecondHeight = mSecondPart.getMeasuredHeight();        System.out.println("----------onLayout-------------");        System.out.println("mFistPart:" + mFistPart + " mSecondPart:" + mSecondPart);        System.out.println("mFistPart.getMeasuredHeight():" + mFistHeight + " mSecondPart.getMeasuredHeight():" + mSecondHeight);        System.out.println("mFistPart.getHeight():" + mFistPart.getHeight() + " mSecondPart.getHeight():" + mSecondPart.getHeight());    }}

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:

System.out: ----------Constructor-------------System.out: mFistPart:null mSecondPart:nullSystem.out: ----------onFinishInflate-------------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}System.out: mFistPart.getMeasuredHeight():0 mSecondPart.getMeasuredHeight():0System.out: mFistPart.getHeight():0 mSecondPart.getHeight():0System.out: ----------onMeasure-------------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}System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():328System.out: mFistPart.getHeight():0 mSecondPart.getHeight():0System.out: ----------onMeasure-------------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}System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424System.out: mFistPart.getHeight():0 mSecondPart.getHeight():0System.out: ----------onSizeChanged-------------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}System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424System.out: mFistPart.getHeight():0 mSecondPart.getHeight():0System.out: ----------onLayout-------------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}System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424System.out: mFistPart.getHeight():600 mSecondPart.getHeight():424System.out: ----------addOnGlobalLayoutListener-------------System.out: mFistPart.getMeasuredHeight():600mFistPart.getHeight():600System.out: ----------addOnGlobalLayoutListener-------------System.out: mFistPart.getMeasuredHeight():424mFistPart.getHeight():424System.out: ----------onWindowFocusChanged-------------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:trueSystem.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424System.out: mFistPart.getHeight():600 mSecondPart.getHeight():424System.out: ----------onMeasure-------------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}System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424System.out: mFistPart.getHeight():600 mSecondPart.getHeight():424System.out: ----------onLayout-------------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}System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424System.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.