title: android - setting LayoutParams programmatically
body: <p>I putting an in-game chat module into an app. I am adding text messages as they are received into a LinearLayout view. I want to set the layout params to the TextView but the following code is crashing and the error messages befuddle me.</p>
  
  <pre><code>private void addChat(String chat, String when,  Boolean mine) {
      int leftMargin;
  
      TextView tv = new TextView(this);
      llview.addView(tv);
      tv.setTextColor(Color.WHITE);
      tv.setTextSize(2,25);
      tv.setText(chat);
      if (mine) {
          leftMargin = 5;
          tv.setBackgroundColor(0x7C5B77);
      }
      else {
          leftMargin = 50;
          tv.setBackgroundColor(0x778F6E);
      }
      final ViewGroup.MarginLayoutParams lpt =(MarginLayoutParams)tv.getLayoutParams();
      lpt.setMargins(leftMargin,lpt.topMargin,lpt.rightMargin,lpt.bottomMargin);
  
      tv.setLayoutParams(new ViewGroup.LayoutParams(
              ViewGroup.LayoutParams.WRAP_CONTENT,
              ViewGroup.LayoutParams.WRAP_CONTENT));
  
  }
  </code></pre>
  
  <p>when it runs, all of the above code executes but it crashes in android runtime as:</p>
  
  <pre><code>03-13 14:15:38.513: E/AndroidRuntime(12985): java.lang.ClassCastException:      android.view.ViewGroup$LayoutParams
  </code></pre>
  
  <p>and stepping through with the debugger, it actually processes all of these lines</p>
  
  <p>but then barfs when trying to render with an equally cryptic exception detailed message:</p>
  
  <pre><code>android.view.ViewGroup$LayoutParams
  </code></pre>
  
  <p>So, what have done to get to this state? What should I be doing to have alternating left/right indented messages ? </p>