（4.1.6.1）getMeasuredHeight()与getHeight的区别

最新推荐文章于 2019-02-21 14:45:01 发布

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本文详细解析了Android中View的高度获取方法getHeight()与getMeasuredHeight()的区别。探讨了这两种方法的具体应用场景，以及它们在View生命周期中的调用时机。通过源码分析，揭示了这两种方法返回值的真正含义。

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前提知识点：
1. 在一个类初始化时，即在构造函数当中是得不到View的实际大小的。getWidth()和getMeasuredWidth()得到的结果都是0，但是可以从onDraw()方法或者dispatchDraw()方法里面获得。可以通过调用invalidate()来执行onDraw()和dispatchDraw()方法。
2. 这两个方法所得到的结果的单位是像素即pixel

我们分析下这两个方法的不同，先看官方文档：

这里写图片描述

getHeight 表示的是 View实际绘制出来的的大小
getMeasuredHeight()是实际View的大小，也就是在父容器在计算当前view大小时，当前View的OnMeasure中设置的大小，与屏幕无关，与父容器大小无关。
getMeasuredHeight()与getHeight()并没有直接关系，但是我们在layout的时候一般会遵循一定的原则

getMeasuredHeight取出的就是setMeasuredDimension的值

当然，上述其实只是一个概念，我们进一步的研究下，按照我们一个自定义View的过程中，我们会在onMeasure(int widthMeasureSpec, int heightMeasureSpec)方法中完成测量后，必须调用View#setMeasuredDimension(int measuredWidth, int measuredHeight)：

    protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) {
        boolean optical = isLayoutModeOptical(this);
        if (optical != isLayoutModeOptical(mParent)) {
            Insets insets = getOpticalInsets();
            int opticalWidth  = insets.left + insets.right;
            int opticalHeight = insets.top  + insets.bottom;

            measuredWidth  += optical ? opticalWidth  : -opticalWidth;
            measuredHeight += optical ? opticalHeight : -opticalHeight;
        }
        setMeasuredDimensionRaw(measuredWidth, measuredHeight);
    }

其最终调用:

    private void setMeasuredDimensionRaw(int measuredWidth, int measuredHeight) {
        mMeasuredWidth = measuredWidth;
        mMeasuredHeight = measuredHeight;

        mPrivateFlags |= PFLAG_MEASURED_DIMENSION_SET;
    }

而我们getMeasuredHeight()取出来的就是mMeasuredHeight ：

    public final int getMeasuredHeight() {
        return mMeasuredHeight & MEASURED_SIZE_MASK;
    }

getHeight 取出的是父布局在绘制当前View的onLayout（）中调用child.Layout（。。。）传入的参数

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        Log.e("test", "MyViewGroup.onLayout  left = " + l + "  top = " + t + "  right = " + r + "  bottom = " + b);
        View view = getChildAt(0);
        int d = 200;
        d = -d;
//        d = t;
//        view.layout(0, 0, view.getMeasuredWidth(), view.getMeasuredHeight());

        l = -100 + new Random().nextInt(100);
        t = 0;
        r = view.getMeasuredWidth() - 100;
        b = view.getMeasuredHeight() - 100;
        //view.getHeight= t- b;
        view.layout(l, t, r, b);
    }

  public void layout(int l, int t, int r, int b) {
        if ((mPrivateFlags3 & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) != 0) {
            onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec);
            mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
        }

        int oldL = mLeft;
        int oldT = mTop;
        int oldB = mBottom;
        int oldR = mRight;

        boolean changed = isLayoutModeOptical(mParent) ?
                setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);

        if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {
            onLayout(changed, l, t, r, b);
            mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;

            ListenerInfo li = mListenerInfo;
            if (li != null && li.mOnLayoutChangeListeners != null) {
                ArrayList<OnLayoutChangeListener> listenersCopy =
                        (ArrayList<OnLayoutChangeListener>)li.mOnLayoutChangeListeners.clone();
                int numListeners = listenersCopy.size();
                for (int i = 0; i < numListeners; ++i) {
                    listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB);
                }
            }
        }

        mPrivateFlags &= ~PFLAG_FORCE_LAYOUT;
        mPrivateFlags3 |= PFLAG3_IS_LAID_OUT;
    }

我们来看看getHeight():

    public final int getHeight() {
        return mBottom - mTop;
    }