View.getWidth()在onCreate方法中不起作用？

Question

为什么lColorWheel.getWith()方法返回0？我想这与onMeasure事件有关,但我真的无法从文档中了解它是如何工作的.我必须为mDrawable设置尺寸？

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

    ShapeDrawable mDrawable;
    ivColorWheel=(ImageView)findViewById(R.id.ivColorWheel);
    lColorWheel=findViewById(R.id.lColorWheel);
    ld=(LayerDrawable)getResources().getDrawable(R.drawable.colorwheel);  

    mDrawable = new ShapeDrawable(new OvalShape());

    mDrawable.setIntrinsicWidth(lColorWheel.getWidth());
    mDrawable.setIntrinsicHeight(lColorWheel.getHeight());
    Log.d("lColorWheel.getWidth()",Integer.toString(lColorWheel.getWidth())); //returns 0, why?
    Log.d("lColorWheel.getHeight()",Integer.toString(lColorWheel.getHeight())); //returns 0, why ?

和适当的XML文件:

<RelativeLayout 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"
android:background="@drawable/background"
android:gravity="center_horizontal"
android:addStatesFromChildren="true" >

<RelativeLayout
    android:id="@+id/lColorWheel"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_marginLeft="20dp"
    android:layout_marginRight="20dp"
    android:layout_marginTop="20dp" 
    android:layout_centerHorizontal="true" 
    android:adjustViewBounds="true">

     <ImageView
        android:id="@+id/ivColorWheel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:adjustViewBounds="true"
        android:paddingBottom="0dp"
        android:paddingTop="0dp"
        android:src="@drawable/iconwheel"
        />

      <ImageView
          android:id="@+id/ivCenterButton1"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_centerHorizontal="true"
          android:layout_centerVertical="true"
          android:maxHeight="5dp"
          android:maxWidth="5dp"
          android:onClick="clc"
          android:paddingBottom="0dp"
          android:paddingLeft="0dp"
          android:paddingRight="0dp"
          android:paddingTop="0dp"
          android:src="@drawable/center3" />

</RelativeLayout>

<SeekBar
     android:id="@+id/sbColorIntensity"
     android:layout_width="match_parent"
     android:layout_height="50dp"
     android:layout_alignParentLeft="true"
      android:layout_below="@id/lColorWheel"
     android:layout_marginLeft="20dp"
     android:layout_marginRight="20dp"
     android:layout_marginTop="20dp"
     android:background="@drawable/colorintensitystrip"
     android:max="255"
     android:maxHeight="-25dp"
     android:thumb="@drawable/thumb"
     android:thumbOffset="0dp"
 />



<SeekBar
    android:id="@+id/sbOrientation"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:layout_alignParentLeft="true"
    android:layout_below="@id/sbColorIntensity"
    android:layout_marginLeft="20dp"
    android:layout_marginRight="20dp"
    android:layout_marginTop="20dp"
    android:background="@drawable/orientationstrip"
    android:max="255"
    android:maxHeight="-25dp"
    android:thumb="@drawable/thumb"
    android:thumbOffset="0dp"
     />

<SeekBar
    android:id="@+id/sbWhiteIntensity"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:layout_alignParentLeft="true"
    android:layout_below="@id/sbOrientation"
    android:layout_marginLeft="20dp"
    android:layout_marginRight="20dp"
    android:layout_marginTop="20dp"
    android:background="@drawable/whiteintensitystrip"
    android:max="255"
    android:maxHeight="-25dp"
    android:thumb="@drawable/thumb"
    android:thumbOffset="0dp"
     />
 </RelativeLayout>

谢谢

Answer 1

如果要在渲染完成之前使用它们,则需要测量视图的高度和宽度.

以下代码将帮助您测量任何视图的高度和宽度.

imgView.measure(
    MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED),
    MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));
imgView.layout(0, 0,
    imgView.getMeasuredWidth(),
    imgView.getMeasuredHeight());

在使用视图的高度和宽度之前编写此代码.

有时这种方法不会给出正确的结果.还有其他选择.下面的代码将在屏幕上绘制之前计算高度和宽度.

ViewTreeObserver viewTree = imgView.getViewTreeObserver();
viewTree.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
    public boolean onPreDraw() {
        finalHeight = imgView.getMeasuredHeight();
        finalWidth = imgView.getMeasuredWidth();
        //print or do some code
        return true;
    }
});