OnMeasure get wrong value when in XML width and height are all fixed

Question

I was developing a customized view when I encountered this problem. In the XML I set the layout_width & layout_height with fixed value 100dp. But in onMeaure() method I got widthMeasureSpec with measureMode EXACTLY, but heightMeasureSpec with measureMode AT_MOST. What's more weird is that they come with different size value. Here's the XML and related code fragment:

CODE:

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

    int widthMeasureMode = MeasureSpec.getMode(widthMeasureSpec);
    int widthMeasureSize = MeasureSpec.getSize(widthMeasureSpec);
    int heightMeasureMode = MeasureSpec.getMode(heightMeasureSpec);
    int heightMeasureSize = MeasureSpec.getSize(heightMeasureSpec);
}

XML:

<com.my.view
    android:layout_width="100dp"
    android:layout_height="100dp"
    android:background="@color/theme"
    app:contentSizeRatio="50%"
    app:imageSource="@drawable/ic_logo_white_48"/>