The EditText widget has a string property named Error, which simplifies the effort of displaying errors to the user, particularly if you want to be able to show all the fields with errors at once. The following screenshot displays the error received for leaving the Name field empty:

To use this facility, simply set the property to an error message and clear the property when no errors exist. The following example demonstrates implementing the rule for the Name property.

bool errors = false;

if (String.IsNullOrEmpty (_nameEditText.Text)) {
_nameEditText.Error = "Name cannot be empty";
  errors = true;
}
else
  _nameEditText.Error = null;

Notice the local Boolean variable named errors, which is used to keep track of whether any errors have been found. Edits for Latitude and Longitude are a little more involved, as you need to account for converting text to a double value and allow for a null value to be specified. The following code demonstrates one of the approaches to implement the edits:

double? tempLatitude = null;
if (!String.IsNullOrEmpty(_latEditText.Text)) {
  try {
    tempLatitude = Double.Parse(_latEditText.Text);
    if ((tempLatitude > 90) | (tempLatitude < -90)) {
      _latEditText.Error = "Latitude must be a decimal valuebetween -90 and 90";
      errors = true;
    }
    else
      _latEditText.Error = null;
  }
  catch {
    _latEditText.Error = "Latitude must be valid decimal number";
  errors = true;
  }
}

Implement the rules identified at the start of this section in the SavePOI() method using the EditText.Error property.

The actual updating of the POI properties and saving should only be performed if all of the edits are passed. The following listing shows one of the ways to structure the logic:

if (!errors) {
  _poi.Name = _nameEditText.Text;
  _poi.Description = _descrEditText.Text;
  _poi.Address = _addrEditText.Text;
  _poi.Latitude = tempLatitude;
  _poi.Longitude = tempLongitude;
  POIData.Service.SavePOI (_poi);
  Finish ();
}

Notice that the Finish() method is called at the end of the preceding code snippet. This causes the POIDetailActivity activity to be closed and the previous activity on the stack will be brought back to the foreground; in our case, POIListActivity. Refer to the code bundle for a more complete example.

Run POIApp and confirm that the validations are working correctly.