(Sample code by Steve Garman posted in the DroidScript Google Group)

Please note that this sample does not allow negative numbers but it does allow more than 1 dot, so the string will still need to be checked later to see if it is a valid number. You can look at this sample too.

//Called when application is started.
function OnStart()
{
    //Create a layout with objects vertically centered.
    lay = app.CreateLayout( "linear", "VCenter,FillXY" );    
 
    //Create a text label and add it to layout.
    txt = app.CreateTextEdit( "",-1,-1,"Number" );
    txt.lastPos=0;
    txt.SetOnChange( txtOnChange );
    lay.AddChild( txt );
 
    //Add layout to app.    
    app.AddLayout( lay );
}
 
function txtOnChange()
{
   var s1 = this.GetText();
   var s2 = s1.replace(/[^0-9\.]/g, "");
   if(s1 != s2)
   {
      this.SetText(s2);
      this.SetCursorPos(this.lastPos); 
   }else
   {
      this.lastPos = this.GetCursorPos();
 
   }
}