關於View的getWidth()和getMeasuredWidth()的知識總結

半夏微涼sheila發表於2017-12-16

1、View的getWidth()和getMeasuredWidth()有什麼區別嗎？

View 的寬高是由 View 本身和 parent 容器共同決定的。

getMeasuredWidth() 與 getWidth() 分別對應於檢視繪製的 measure 與 layout 階段。 getMeasuredWidth()(int widthMeasureSpec, int heightMeasureSpec)方法裡面獲得的，而getWidth()是在onLayout()方法中獲得的。大部分情況下他們是相等，也有一些不相等的情況。比如在父佈局的onLayout()方法或者此View的onDraw()方法裡呼叫measure(0,0);(measure中的引數的值你自己可以定義)的話，兩者的結果可能會不同。

getWidth()原始碼：

/**
     * 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;
    }
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從原始碼可以看出getWidth()返回的是右邊座標減輕座標減去左邊座標，這要在佈局之後才能確定它們的座標，也就是說在佈局後onLayout()方法裡面才能呼叫getWidth()來獲取。所以getWidth()獲得的寬度是View在設定好佈局後整個View的寬度。

getMeasuredWidth()原始碼：

/**
     * Like {@link #getMeasuredWidthAndState()}, but only returns the
     * raw width component (that is the result is masked by
     * {@link #MEASURED_SIZE_MASK}).
     * @return The raw measured width of this view.
     */
    public final int getMeasuredWidth() {
        return mMeasuredWidth & MEASURED_SIZE_MASK;
    }
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從原始碼可以看出getMeasuredWidth()返回的是此檢視的原始測量寬度。所以說getMeasuredWidth()是對View上的內容進行測量後得到的View內容佔據的寬度。

一般情況下，getMeasuredWidth()和getWidth()獲得的結果是一樣的，但是如果在父佈局的onLayout()方法或者此View的onDraw()方法裡呼叫measure(0,0);(measure中的引數的值你自己可以定義)的話，兩者的結果可能會不同。

例如：

public class CustomView extends android.support.v7.widget.AppCompatTextView {
    
    private String TAG = CustomView.class.getSimpleName();
    
    public CustomView(Context context) {
        super(context);
    }

    public CustomView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    public CustomView(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 left, int top, int right, int bottom) {
        super.onLayout(changed, left + 10, top, right + 10, bottom + 10);
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        measure(0, 0);
        Log.d(TAG, "width=" + getWidth());
        Log.d(TAG, "height=" + getHeight());
        Log.d(TAG, "MeasuredWidth=" + getMeasuredWidth());
        Log.d(TAG, "MeasuredHeight=" + getMeasuredHeight());
    }
}
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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:orientation="vertical"
    android:layout_height="match_parent"
    tools:context="com.shzx.viewdemo.MainActivity">
    <com.shzx.viewdemo.CustomView
        android:id="@+id/customView"
        android:layout_width="100dp"
        android:text="ceshi"
        android:layout_height="100dp" />
</LinearLayout>
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此時的列印結果是

12-16 07:13:40.050 8901-8901/com.shzx.viewdemo D/CustomView: width=350
12-16 07:13:40.050 8901-8901/com.shzx.viewdemo D/CustomView: height=350
12-16 07:13:40.050 8901-8901/com.shzx.viewdemo D/CustomView: MeasuredWidth=116
12-16 07:13:40.050 8901-8901/com.shzx.viewdemo D/CustomView: MeasuredHeight=66
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此時getWidth()和getMeasuredWidth()不相等

因此可以得出 getWidth(): View在設定好佈局後整個View的寬度。getMeasuredWidth(): 對View上的內容進行測量後得到的View內容佔據的寬度

2、如何在onCreate中拿到View的寬度和高度？

在onCreate()中獲取View的寬高有三種方法：獲取view的寬高

private void getWidthHeight() {
        int width = customView.getWidth();
        int height = customView.getHeight();
        LogUtils.e("width =" + width);
        LogUtils.e("height =" + height);

        int measuredWidth = customView.getMeasuredWidth();
        int measuredHeight = customView.getMeasuredHeight();
        LogUtils.e("measuredWidth =" + measuredWidth);
        LogUtils.e("measuredHeight =" + measuredHeight);
    }
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1)、View.post(runnable)

利用 Handler 通訊機制，傳送一個 Runnable 到 message queue 中，當 view layout 處理完成時，自動傳送訊息，通知 UI 執行緒。藉此機制，巧妙獲取 View 的寬高屬性。程式碼簡潔，使用簡單，相比 ViewTreeObserver 監聽處理，還不需要手動移除觀察者監聽事件。

 customView.post(new Runnable() {
            @Override
            public void run() {
            getWidthHeight();
            }
        });
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列印結果：

12-16 02:33:49.938 4238-4238/com.shzx.viewdemo E/MainActivity: width =116>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity$1,methodName=run,lineNumber=23 ] 
12-16 02:33:49.941 4238-4238/com.shzx.viewdemo E/MainActivity: height =66>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity$1,methodName=run,lineNumber=24 ] 
12-16 02:33:49.941 4238-4238/com.shzx.viewdemo E/MainActivity: measuredWidth =116>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity$1,methodName=run,lineNumber=28 ] 
12-16 02:33:49.946 4238-4238/com.shzx.viewdemo E/MainActivity: measuredHeight =66>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity$1,methodName=run,lineNumber=29 ] 

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2)、ViewTreeObserver.addOnGlobalLayoutListener(OnGlobalLayoutListener listener)

監聽 View 的 onLayout() 繪製過程，一旦 layout 觸發變化，立即回撥 onLayoutChange 方法。

注意，使用完也要注意呼叫 removeOnGlobalLayoutListener() 方法移除監聽事件。避免後續每一次發生全域性 View 變化均觸發該事件，影響效能。

ViewTreeObserver observer = customView.getViewTreeObserver();
        observer.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                getWidthHeight();
                customView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
            }
        });
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列印結果：

12-16 03:34:06.981 6116-6116/com.shzx.viewdemo E/MainActivity: width =116>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=getWidthHeight,lineNumber=61 ] 
12-16 03:34:06.982 6116-6116/com.shzx.viewdemo E/MainActivity: height =66>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=getWidthHeight,lineNumber=62 ] 
12-16 03:34:06.983 6116-6116/com.shzx.viewdemo E/MainActivity: measuredWidth =116>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=getWidthHeight,lineNumber=66 ] 
12-16 03:34:06.983 6116-6116/com.shzx.viewdemo E/MainActivity: measuredHeight =66>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=getWidthHeight,lineNumber=67 ] 
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3)、View.measure(int widthMeasureSpec,int heightMeasureSpec)

View.MeasureSpec.makeMeasureSpec(@IntRange(from = 0, to = (1 << MeasureSpec.MODE_SHIFT) - 1) int size, @MeasureSpecMode int mode)

其中 MeasureSpec.MODE_SHIFT = 30

size最大值為 (1<<30)-1，即用30位二進位制表示，也就是說最大是30個1 (即2^30-1)。

        int widthMeasureSpec = View.MeasureSpec.makeMeasureSpec(200, View.MeasureSpec.EXACTLY);
        int heigthMeasureSpec = View.MeasureSpec.makeMeasureSpec(200, View.MeasureSpec.EXACTLY);

        customView.measure(widthMeasureSpec,heigthMeasureSpec);

        int width = customView.getWidth();
        int height = customView.getHeight();
        LogUtils.e("width =" + width);
        LogUtils.e("height =" + height);

        int measuredWidth = customView.getMeasuredWidth();
        int measuredHeight = customView.getMeasuredHeight();
        LogUtils.e("measuredWidth =" + measuredWidth);
        LogUtils.e("measuredHeight =" + measuredHeight);
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列印結果：

12-16 03:04:23.278 5444-5444/com.shzx.viewdemo E/MainActivity: width =0>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=onCreate,lineNumber=42 ] 
12-16 03:04:23.278 5444-5444/com.shzx.viewdemo E/MainActivity: height =0>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=onCreate,lineNumber=43 ] 
12-16 03:04:23.278 5444-5444/com.shzx.viewdemo E/MainActivity: measuredWidth =200>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=onCreate,lineNumber=47 ] 
12-16 03:04:23.278 5444-5444/com.shzx.viewdemo E/MainActivity: measuredHeight =200>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=onCreate,lineNumber=48 ] 
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        int widthMeasureSpec = View.MeasureSpec.makeMeasureSpec((1 << 30) - 1, View.MeasureSpec.AT_MOST);
        int heigthMeasureSpec = View.MeasureSpec.makeMeasureSpec((1 << 30) - 1, View.MeasureSpec.AT_MOST);

        customView.measure(widthMeasureSpec,heigthMeasureSpec);

        int width = customView.getWidth();
        int height = customView.getHeight();
        LogUtils.e("width =" + width);
        LogUtils.e("height =" + height);

        int measuredWidth = customView.getMeasuredWidth();
        int measuredHeight = customView.getMeasuredHeight();
        LogUtils.e("measuredWidth =" + measuredWidth);
        LogUtils.e("measuredHeight =" + measuredHeight);
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列印結果：

12-16 03:03:28.394 5344-5344/com.shzx.viewdemo E/MainActivity: width =0>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=onCreate,lineNumber=42 ] 
12-16 03:03:28.395 5344-5344/com.shzx.viewdemo E/MainActivity: height =0>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=onCreate,lineNumber=43 ] 
12-16 03:03:28.395 5344-5344/com.shzx.viewdemo E/MainActivity: measuredWidth =116>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=onCreate,lineNumber=47 ] 
12-16 03:03:28.395 5344-5344/com.shzx.viewdemo E/MainActivity: measuredHeight =66>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=onCreate,lineNumber=48 ] 
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除了在onCreate()中獲得View的寬高，還可以在Activity的onWindowFocusChanged(boolean hasFocus)方法中獲取寬高

原始碼：

 /**
     * Called when the current {@link Window} of the activity gains or loses
     * focus.  This is the best indicator of whether this activity is visible
     * to the user.  The default implementation clears the key tracking
     * state, so should always be called.
     *
     * <p>Note that this provides information about global focus state, which
     * is managed independently of activity lifecycles.  As such, while focus
     * changes will generally have some relation to lifecycle changes (an
     * activity that is stopped will not generally get window focus), you
     * should not rely on any particular order between the callbacks here and
     * those in the other lifecycle methods such as {@link #onResume}.
     *
     * <p>As a general rule, however, a resumed activity will have window
     * focus...  unless it has displayed other dialogs or popups that take
     * input focus, in which case the activity itself will not have focus
     * when the other windows have it.  Likewise, the system may display
     * system-level windows (such as the status bar notification panel or
     * a system alert) which will temporarily take window input focus without
     * pausing the foreground activity.
     *
     * @param hasFocus Whether the window of this activity has focus.
     *
     * @see #hasWindowFocus()
     * @see #onResume
     * @see View#onWindowFocusChanged(boolean)
     */
    public void onWindowFocusChanged(boolean hasFocus) {
    }
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 @Override
    public void onWindowFocusChanged(boolean hasFocus) {
        super.onWindowFocusChanged(hasFocus);
        getWidthHeight();
    }
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列印結果：

12-16 03:46:36.929 6425-6425/com.shzx.viewdemo E/MainActivity: width =116>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=getWidthHeight,lineNumber=58 ] 
12-16 03:46:36.929 6425-6425/com.shzx.viewdemo E/MainActivity: height =66>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=getWidthHeight,lineNumber=59 ] 
12-16 03:46:36.929 6425-6425/com.shzx.viewdemo E/MainActivity: measuredWidth =116>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=getWidthHeight,lineNumber=63 ] 
12-16 03:46:36.929 6425-6425/com.shzx.viewdemo E/MainActivity: measuredHeight =66>>>[ threadID=1,threadName=main,fileName=MainActivity.java,className=com.shzx.viewdemo.MainActivity,methodName=getWidthHeight,lineNumber=64 ] 
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關於View的getWidth()和getMeasuredWidth()的知識總結

1、View的getWidth()和getMeasuredWidth()有什麼區別嗎？

getWidth()原始碼：

getMeasuredWidth()原始碼：

從原始碼可以看出getMeasuredWidth()返回的是此檢視的原始測量寬度。所以說getMeasuredWidth()是對View上的內容進行測量後得到的View內容佔據的寬度。

因此可以得出 getWidth(): View在設定好佈局後整個View的寬度。getMeasuredWidth(): 對View上的內容進行測量後得到的View內容佔據的寬度

2、如何在onCreate中拿到View的寬度和高度？

1)、View.post(runnable)

2)、ViewTreeObserver.addOnGlobalLayoutListener(OnGlobalLayoutListener listener)

監聽 View 的 onLayout() 繪製過程，一旦 layout 觸發變化，立即回撥 onLayoutChange 方法。

注意，使用完也要注意呼叫 removeOnGlobalLayoutListener() 方法移除監聽事件。避免後續每一次發生全域性 View 變化均觸發該事件，影響效能。

3)、View.measure(int widthMeasureSpec,int heightMeasureSpec)

View.MeasureSpec.makeMeasureSpec(@IntRange(from = 0, to = (1 << MeasureSpec.MODE_SHIFT) - 1) int size, @MeasureSpecMode int mode)

其中 MeasureSpec.MODE_SHIFT = 30

size最大值為 (1<<30)-1， 即用30位二進位制表示，也就是說最大是30個1 (即2^30-1)。

除了在onCreate()中獲得View的寬高，還可以在Activity的onWindowFocusChanged(boolean hasFocus)方法中獲取寬高

相關文章

size最大值為 (1<<30)-1，即用30位二進位制表示，也就是說最大是30個1 (即2^30-1)。