自定义view2--getMeasuredWidth和getWidth方法区分

   从源代码的角度发现：

   1.对于-getMeasuredWidth打开源码发现

 

**

* Like {@link#getMeasuredWidthAndState()}, but only returns the

* raw width component (that is the result is masked by

* {@link#MEASURED_SIZE_MASK}).

*

*@returnThe raw measured width of this view.

*/

public final intgetMeasuredWidth() {

returnmMeasuredWidth& MEASURED_SIZE_MASK;

}

这里我们看到它的返回值与mMeasuredWidth相关，这个mMeasuredWidth是哪儿来的呢？

看源码setMeasuredDimension：

protected final voidsetMeasuredDimension(intmeasuredWidth, intmeasuredHeight) {

booleanoptical =isLayoutModeOptical(this);

if(optical !=isLayoutModeOptical(mParent)) {

Insets insets = getOpticalInsets();

intopticalWidth = insets.left + insets.right;

intopticalHeight = insets.top + insets.bottom;

measuredWidth += optical ? opticalWidth : -opticalWidth;

measuredHeight += optical ? opticalHeight : -opticalHeight;

}

setMeasuredDimensionRaw(measuredWidth,measuredHeight);

}

其中 setMeasuredDimensionRaw(源码：

private voidsetMeasuredDimensionRaw(intmeasuredWidth, intmeasuredHeight) {

mMeasuredWidth= measuredWidth;

mMeasuredHeight= measuredHeight;

mPrivateFlags|= PFLAG_MEASURED_DIMENSION_SET;

}

所以可以得等到getMeasuredWidth实际上是从setMeasuredDimension（）中传递过来的参数

2.对于getWidth

/** * Return the width of the your view. * * @return The width of your view, in pixels. */@ViewDebug.ExportedProperty(category = "layout")public final int getWidth() {    return mRight - mLeft;}

可以发现结果与

mRight - mLeft;有关

那么这两个变量来自哪里呢？接着看源码发现 其实它是onlayout过程传过来的四个参数中的两个，那还等什么去看看

onlayout源码

protected void onLayout(boolean changed, int left, int top, int right, int bottom) {}/** * Assign a size and position to this view. * * This is called from layout. * * @param left Left position, relative to parent * @param top Top position, relative to parent * @param right Right position, relative to parent * @param bottom Bottom position, relative to parent * @return true if the new size and position are different than the *         previous ones * {@hide} */protected boolean setFrame(int left, int top, int right, int bottom) {    boolean changed = false;    if (DBG) {        Log.d("View", this + " View.setFrame(" + left + "," + top + ","                + right + "," + bottom + ")");    }    if (mLeft != left || mRight != right || mTop != top || mBottom != bottom) {        changed = true;        // Remember our drawn bit        int drawn = mPrivateFlags & PFLAG_DRAWN;        int oldWidth = mRight - mLeft;        int oldHeight = mBottom - mTop;        int newWidth = right - left;        int newHeight = bottom - top;        boolean sizeChanged = (newWidth != oldWidth) || (newHeight != oldHeight);        // Invalidate our old position        invalidate(sizeChanged);        mLeft = left;        mTop = top;        mRight = right;        mBottom = bottom;        mRenderNode.setLeftTopRightBottom(mLeft, mTop, mRight, mBottom);        mPrivateFlags |= PFLAG_HAS_BOUNDS;        if (sizeChanged) {            sizeChange(newWidth, newHeight, oldWidth, oldHeight);        }        if ((mViewFlags & VISIBILITY_MASK) == VISIBLE || mGhostView != null) {            // If we are visible, force the DRAWN bit to on so that            // this invalidate will go through (at least to our parent).            // This is because someone may have invalidated this view            // before this call to setFrame came in, thereby clearing            // the DRAWN bit.            mPrivateFlags |= PFLAG_DRAWN;            invalidate(sizeChanged);            // parent display list may need to be recreated based on a change in the bounds            // of any child            invalidateParentCaches();        }        // Reset drawn bit to original value (invalidate turns it off)        mPrivateFlags |= drawn;        mBackgroundSizeChanged = true;        if (mForegroundInfo != null) {            mForegroundInfo.mBoundsChanged = true;        }        notifySubtreeAccessibilityStateChangedIfNeeded();    }    return changed;}

 到这里我们找到了getWidth方法的返回值的两个参数①mRight②mLeft。这样大家明白了getWidth返回值了吗？

综述：

①getMeasuredWidth方法获得的值是setMeasuredDimension方法设置的值，它的值在measure方法运行后就会确定

②getWidth方法获得是layout方法中传递的四个参数中的mRight-mLeft，它的值是在layout方法运行后确定的

③一般情况下在onLayout方法中使用getMeasuredWidth方法，而在除onLayout方法之外的地方用getWidth方法。