Why is onMeasure() called twice in my custom View?

Question

Below is my code for my custom View:

XML layout:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res/com.project.summary"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" 
    android:background="@color/BgColor">

    <com.project.summary.customview.CustomView
        android:id="@+id/customView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:colorValue="@color/textRed"
        app:textString="This the Custom View!!!"
        app:textSize="20sp"
        />

</LinearLayout>

Code in my CustomView.java:

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    Log.e("140117", "onMeasure()"+this.getHeight()+"||"+this.getWidth());
}

Code of the test activity:

    public class CustomViewActivity extends Activity{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.customview_layout);
    }
}

logcat output:

01-17 13:47:01.203: E/140117(11467): onMeasure()0||0
01-17 13:47:01.243: E/140117(11467): onMeasure()28||212

I searched StackOverflow, but no one give an clear answer. Could someone help me?

Answer 1

A parent View may call measure() more than once on its children. For example, the parent may measure each child once with unspecified dimensions to find out how big they want to be, then call measure() on them again with actual numbers if the sum of all the children's unconstrained sizes is too big or too small (that is, if the children don't agree among themselves as to how much space they each get, the parent will intervene and set the rules on the second pass). as https://developer.android.com/guide/topics/ui/how-android-draws.html says.