android中getWidth()和getMeasuredWidth()之間的區別

     先給出一個結論：getMeasuredWidth()獲取的是view原始的大小，也就是這個view在XML文件中配置或者是代碼中設置的大小。getWidth（）獲取的是這個view最終顯示的大小，這個大小有可能等於原始的大小也有可能不等於原始大小。

     從源碼上開始分析一下這兩個方法的區別。首先來看一下getMeasuredWidth()這個方法。

  public final int getMeasuredWidth() {
        return mMeasuredWidth & MEASURED_SIZE_MASK;
    }

  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
 setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
                getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
    }

  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);
    }

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

        mPrivateFlags |= PFLAG_MEASURED_DIMENSION_SET;
    }

   從源碼上來看，getMeasuredWidth（）獲取的是mMeasuredWidth的這個值。這個值是一個8位的十六進制的數字，高兩位表示的是這個measure階段的Mode的值，具體可以查看MeasureSpec的原理。這里mMeasuredWidth & MEASURED_SIZE_MASK表示的是測量階段結束之后，view真實的值。而且這個值會在調用了setMeasuredDimensionRaw（）函數之后會被設置。所以getMeasuredWidth（）的值是measure階段結束之后得到的view的原始的值。

 

     再來看看getWidth（）的源碼：

  public final int getWidth() {
        return mRight - mLeft;
    }

   那么問題來了，mRight和mLeft是什么值，是在什么時候被設置的。我們再看layout階段的源碼：

  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);

      ... 
}

   在layout階段會去調用setOpticalFrame（）或者調用setFrame（）方法，從源碼中可知setOpticalFrame（）方法，最終還是調用的setFrame（）方法。

  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;
   ...
}

  所以最終的mLeft和mRight的值是在setFrame（）方法中被設置的。而且這些mLeft，mRight代表了view最終顯示在界面中的大小。

 

    下面我們自定義一個簡單的ViewGroup，在layout階段改變left，right的值，觀察getMeasuredWidth（）和getWidth（）方法之間的區別。

package com.gearmotion.app.customviewgroup;

import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.widget.RelativeLayout;

/**
 * Created by Charles on 2015/11/21.
 */
public class CustomViewGroup extends RelativeLayout {

    public CustomViewGroup(Context context) {
        super(context);
    }

    public CustomViewGroup(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public CustomViewGroup(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        View child = this.getChildAt(1);  //the textview
        //add 100px for right
        child.layout(child.getLeft(), child.getTop(),child.getRight() + 100,child.getBottom());


    }

<?xml version="1.0" encoding="utf-8"?>
<com.gearmotion.app.customviewgroup.CustomViewGroup 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"
    tools:context="com.gearmotion.app.customviewgroup.MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/left"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="center"
            android:text="width" />

        <Button
            android:id="@+id/right"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="center"
            android:text="measuredWidth" />
    </LinearLayout>

    <TextView
        android:id="@+id/textview"
        android:layout_width="100px"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:background="#8EE5EE"
        android:gravity="center"
        android:text="textview" />

</com.gearmotion.app.customviewgroup.CustomViewGroup>

package com.gearmotion.app.customviewgroup;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    TextView mTextView;
    Button mLeftBtn;
    Button mRightBtn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mTextView = (TextView) this.findViewById(R.id.textview);
        mLeftBtn = (Button) this.findViewById(R.id.left);
        mRightBtn = (Button) this.findViewById(R.id.right);
        mLeftBtn.setOnClickListener(this);
        mRightBtn.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        int id = v.getId();
        switch (id) {
            case R.id.left:   //width
                Toast.makeText(MainActivity.this, "width:" + mTextView.getWidth(), Toast.LENGTH_SHORT).show();
                break;
            case R.id.right:  //measuredWidth
                Toast.makeText(MainActivity.this,"measuredWidth:"+mTextView.getMeasuredWidth(),Toast.LENGTH_SHORT).show();
                break;
        }
    }
}

 在這個demo中，我們給textview設置寬度為100px，但是在layout階段給它加大到200，最終結果是：點擊width按鈕，顯示為200，點解measuredWidth按鈕顯示為100.