1、View的getWidth()和getMeasuredWidth()有什么區(qū)別嗎？

A、賦值時(shí)機(jī)
getMeasureWidth()方法中的值是通過(guò)setMeasuredDimension()方法來(lái)進(jìn)行設(shè)置的。

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

        mPrivateFlags |= PFLAG_MEASURED_DIMENSION_SET;
    }

getWidth()方法中的值則是通過(guò)layout(left,top,right,bottom)方法里的一個(gè)setFrame來(lái)進(jìn)行確定left,top,right,bottom 四個(gè)頂點(diǎn)位置，既初始化mLeft,mTop,mRight,mBottom這四個(gè)值,View的四個(gè)頂點(diǎn)一旦確認(rèn) 那么View在父容器中的位置也就確認(rèn)了.

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

getMeasuredWidth() 當(dāng)View繪制流程中的measure流程結(jié)束以后有值,獲取的是View測(cè)量寬度
getWidth() 當(dāng)View繪制流程中的layout流程結(jié)束之后有值,獲取的是View的實(shí)際高度

正常情況下這兩者獲取的值都是相同的，除非在onMeasure和onLayout過(guò)程之后，在去手動(dòng)調(diào)用measure()這個(gè)方法 去改變對(duì)應(yīng)的數(shù)值，才可能造成兩者值不同.

public class CustomView extends android.support.v7.widget.AppCompatTextView {

    public CustomView(Context context) {
        this(context, null);
    }

    public CustomView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public CustomView(Context context, @Nullable 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 left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right , bottom );
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        measure(0,0);
        int measuredWidth = getMeasuredWidth();
        int measuredHeight = getMeasuredHeight();
        int width = getWidth();
        int height = getHeight();
        Log.e("Charles2", "measuredWidth==" + measuredWidth + "--measuredHeight==" + measuredHeight);
        Log.e("Charles2", "width==" + width + "---height==" + height);
    }

打印日志如下 ：

12-18 15:22:50.878 17332-17332/com.example.administrator.myapplication E/Charles2: measuredWidth==117--measuredHeight==53
12-18 15:22:50.879 17332-17332/com.example.administrator.myapplication E/Charles2: width==275---height==275

2、如何在onCreate中拿到View的寬度和高度？

   (1)重寫 onWindowFocusChanged，需要注意的是此方法會(huì)被調(diào)用多次。當(dāng)Activity的窗口
    得到焦點(diǎn)和失去焦點(diǎn)時(shí)均會(huì)被調(diào)用一次,使用會(huì)頻繁調(diào)用（不推薦）

   (2))View.post (new Runnable)
     通過(guò)post可以將一個(gè)runnable投遞到消息隊(duì)列中，等待Looper調(diào)用次runnable的時(shí)候,View也已經(jīng)初始化好了.

        viewById.post(new Runnable() {
            @Override
            public void run() {
                Log.e("Charles2","寬=" + viewById.getWidth() + " --高=="+ viewById.getHeight());
            }
        });

    (3)ViewTreeObserver,比如使用 OnGlobalLayoutListener這個(gè)接口, 當(dāng)View樹(shù)的狀態(tài)發(fā)生改變或者View樹(shù)的內(nèi)部的View的可見(jiàn)性發(fā)
        生改變。onGlobalLayout方法將被回調(diào),因此可以獲取寬度，但是onGlobalLayout會(huì)被調(diào)用多次.如果使用還必須記得銷毀這個(gè)監(jiān)聽(tīng)(不推薦)

        ViewTreeObserver viewTreeObserver = viewById.getViewTreeObserver();
        viewTreeObserver.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                Log.e("Charles2","寬=" + viewById.getWidth() + " --高=="+ viewById.getHeight());
            }
        });