浅谈自定义View的宽高获取

Posted 2023-01-27 mChenys

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:null
System.out: ----------onFinishInflate-------------
System.out: mFistPart:android.support.v7.widget.AppCompatTextViewfb4034c V.ED..... ......ID 0,0-0,0 mSecondPart:android.support.v7.widget.AppCompatTextView16ebf95 V.ED..... ......ID 0,0-0,0
System.out: mFistPart.getMeasuredHeight():0 mSecondPart.getMeasuredHeight():0
System.out: mFistPart.getHeight():0 mSecondPart.getHeight():0
System.out: ----------onMeasure-------------
System.out: mFistPart:android.support.v7.widget.AppCompatTextViewfb4034c V.ED..... ......ID 0,0-0,0 mSecondPart:android.support.v7.widget.AppCompatTextView16ebf95 V.ED..... ......ID 0,0-0,0
System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():328
System.out: mFistPart.getHeight():0 mSecondPart.getHeight():0

System.out: ----------onMeasure-------------
System.out: mFistPart:android.support.v7.widget.AppCompatTextViewfb4034c V.ED..... ......ID 0,0-0,0 mSecondPart:android.support.v7.widget.AppCompatTextView16ebf95 V.ED..... ......ID 0,0-0,0
System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424
System.out: mFistPart.getHeight():0 mSecondPart.getHeight():0
System.out: ----------onSizeChanged-------------
System.out: mFistPart:android.support.v7.widget.AppCompatTextViewfb4034c V.ED..... ......ID 0,0-0,0 mSecondPart:android.support.v7.widget.AppCompatTextView16ebf95 V.ED..... ......ID 0,0-0,0
System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424
System.out: mFistPart.getHeight():0 mSecondPart.getHeight():0
System.out: ----------onLayout-------------
System.out: mFistPart:android.support.v7.widget.AppCompatTextViewfb4034c V.ED..... ......ID 0,0-720,600 mSecondPart:android.support.v7.widget.AppCompatTextView16ebf95 V.ED..... ......ID 0,600-720,1024
System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424
System.out: mFistPart.getHeight():600 mSecondPart.getHeight():424
System.out: ----------addOnGlobalLayoutListener-------------
System.out: mFistPart.getMeasuredHeight():600mFistPart.getHeight():600
System.out: ----------addOnGlobalLayoutListener-------------
System.out: mFistPart.getMeasuredHeight():424mFistPart.getHeight():424
System.out: ----------onWindowFocusChanged-------------
System.out: mFistPart:android.support.v7.widget.AppCompatTextViewfb4034c V.ED..... ......ID 0,0-720,600 mSecondPart:android.support.v7.widget.AppCompatTextView16ebf95 V.ED..... ......ID 0,600-720,1024 hasWindowFocus:true
System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424
System.out: mFistPart.getHeight():600 mSecondPart.getHeight():424
System.out: ----------onMeasure-------------
System.out: mFistPart:android.support.v7.widget.AppCompatTextViewfb4034c V.ED..... ......ID 0,0-720,600 mSecondPart:android.support.v7.widget.AppCompatTextView16ebf95 V.ED..... ......ID 0,600-720,1024
System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424
System.out: mFistPart.getHeight():600 mSecondPart.getHeight():424
System.out: ----------onLayout-------------
System.out: mFistPart:android.support.v7.widget.AppCompatTextViewfb4034c V.ED..... ......ID 0,0-720,600 mSecondPart:android.support.v7.widget.AppCompatTextView16ebf95 V.ED..... ......ID 0,600-720,1024
System.out: mFistPart.getMeasuredHeight():600 mSecondPart.getMeasuredHeight():424
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.