Question

First off, I’ve been reading this site for years now and it’s helped me out of a bind several times, so thank you to the community here who contribute, and hopefully you can help me with a problem of my own.

I’m just starting out with Android development at my company and I’m attempting to port an existing application from Windows Mobile C# to Android Java. Most of it is going smoothly, but one area I’m having some difficulty is the UI.

The Windows Mobile application reads in a survey specification from a file when the WinForm is created. In the case of a closed-ended question (such as multiple choice), I need to populate the screen with either a CheckBox or RadioButton control for each applicable answer in the spec. Creating the layout and controls required is no problem, but we also have a requirement that the screen does not scroll. Because of this our software needs to be able to calculate the best possible fit within the available screen space without overflow (ie. 1-4 columns used for display) before it’s displayed

I have written my UI (at least the layout) as both an XML resource or Java code, but because methods like GetWidth() and GetHeight() return 0 in onCreate(), I haven’t yet been able to add this required pre-processing.

All of this needs to happen prior to the screen showing. If anyone can point me in the right direction, I would be immensely grateful.

Answer 1

When Android builds the UI from a layout, the root of the layout requests all of it’s children to report their desired size by calling onMeasure(). It does this is a recursive fashion bottom up. if necessary, the parent view will then set the size of the children so that they fit. As you have found, this measuring pass is not finished during onCreate().

Try a global layout listener.

public void onCreate(Bundle savedInstanceState)
{
     super.onCreate(savedInstanceState);

     // inflate your main layout here (use RelativeLayout or whatever your root ViewGroup type is
     LinearLayout mainLayout = (LinearLayout ) this.getLayoutInflater().inflate(R.layout.main, null); 

     // set a global layout listener which will be called when the layout pass is completed and the view is drawn
     mainLayout.getViewTreeObserver().addOnGlobalLayoutListener(
     new ViewTreeObserver.OnGlobalLayoutListener() {
          public void onGlobalLayout() {
               // measure your views here
          }
     }
 );

 setContentView(mainLayout);