title: NumberPicker is not showing in AlertDialog
body: <p>I'm trying to add a NumberPicker to an AlertDialog, but it does not apper even though there seems to be no error. I'm pretty newbie at Android coding so I assume it's something really stupid that's missing there.</p>
  
  <pre><code>        AlertDialog.Builder alert = new AlertDialog.Builder(MainActivity.this);
  
          alert.setTitle("Select the value: ");
  
          NumberPicker np = new NumberPicker(MainActivity.this);
          String[] nums = new String[100];
          for(int i=0; i&lt;nums.length; i++)
                 nums[i] = Integer.toString(i);
  
          np.setMinValue(1);
          np.setMaxValue(nums.length-1);
          np.setWrapSelectorWheel(false);
          np.setDisplayedValues(nums);
          np.setValue(50);
  
          alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
          public void onClick(DialogInterface dialog, int whichButton) {
            // Do something with value!
            }
          });
  
          alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int whichButton) {
              // Cancel.
            }
          });
  
          alert.show();
  </code></pre>