How to calculate EditText value in Android?

In an Android app, I'm using two EditText controls and multiplying their two values. If one EditText is null and in the second one I put a value, it's not working properly. How can I deal with this case, in whi开发者_开发百科ch I have a value in one EditText and a null in the other and I want to multiply the two values?

First of all, you need to have a trigger for when to perform the calculation. Say it's a button, or, even better, every time the value of one of your EditTexts changes:

private EditText editText1,
                 editText2;
private TextView resultsText;

...............................

// Obtains references to your components, assumes you have them defined
// within your Activity's layout file
editText1 = (EditText)findViewById(R.id.editText1);
editText2 = (EditText)findViewById(R.id.editText2);

resultsText = (TextView)findViewById(R.id.resultsText);

// Instantiates a TextWatcher, to observe your EditTexts' value changes
// and trigger the result calculation
TextWatcher textWatcher = new TextWatcher() {
    public void afterTextChanged(Editable s) {
        calculateResult();
    }
    public void beforeTextChanged(CharSequence s, int start, int count, int after){}
    public void onTextChanged(CharSequence s, int start, int before, int count){}
};

// Adds the TextWatcher as TextChangedListener to both EditTexts
editText1.addTextChangedListener(textWatcher);
editText2.addTextChangedListener(textWatcher);

.....................................

// The function called to calculate and display the result of the multiplication
private void calculateResult() throws NumberFormatException {
  // Gets the two EditText controls' Editable values
  Editable editableValue1 = editText1.getText(),
           editableValue2 = editText2.getText();

  // Initializes the double values and result
  double value1 = 0.0,
         value2 = 0.0,
         result;

  // If the Editable values are not null, obtains their double values by parsing
  if (editableValue1 != null)
    value1 = Double.parseDouble(editableValue1.toString());

  if (editableValue2 != null)
    value2 = Double.parseDouble(editableValue2.toString());

  // Calculates the result
  result = value1 * value2;

  // Displays the calculated result
  resultsText.setText(result.toString());
}

On button click it multiplies 2 values of the EditText boxes and checks wether they are empty or not:

private EditText txtOne;
private EditText txtTwo;
private EditText txtResult;
private Button btnCount;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    txtOne = (EditText) findViewById(R.id.editText1);
    txtTwo = (EditText) findViewById(R.id.editText2);
    txtResult = (EditText) findViewById(R.id.editText3);

    btnCount = (Button) findViewById(R.id.button1);
    btnCount.setText("Count");

    btnCount.setOnClickListener(new OnClickListener() {
        public void onClick(View v) {               
            if (txtOne.getText() != null || txtTwo.getText() != null)
                txtResult.setText(String.valueOf(Double.parseDouble(txtOne.getText().toString()) * Double.parseDouble(txtTwo.getText().toString())));       
        }
    });
}

Slight variation of @luvieere code:

//import all the importables

public class MainActivity extends ActionBarActivity 
{

 EditText   Text1,
            Text2;

 double value1,
        value2,
        result;


@Override
protected void onCreate(Bundle savedInstanceState) 
{   
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ResultField = (TextView)findViewById(R.id.ResultField);

    TextWatcher textWatcher = new TextWatcher(){
        public void afterTextChanged(Editable s){
            calcResult(); 
        }
        public void beforeTextChanged(CharSequence s, int start, int count, int after){}
        public void onTextChanged(CharSequence s, int start, int before, int count){}
        };

    Text1 = (EditText)findViewById(R.id.Text1);
    Text2 = (EditText)findViewById(R.id.Text2);

    Text1.addTextChangedListener(textWatcher);
    Text2.addTextChangedListener(textWatcher);
    }


    private void calcResult() throws NumberFormatException {
    Editable editableText1 = Text1.getText(),
            editableText2 = Text2.getText();

    double  value1 = 0.0,
            value2 = 0.0,
            result;

    // NOTE: “&& editableText1.length() >= 1” prevents possible “invalid Double” errors!

    if (editableText1 != null && editableText1.length() >= 1)    
    value1 = Double.parseDouble(editableText1.toString());

    if (editableText2 != null && editableText2.length() >= 1)   
    value2 = Double.parseDouble(editableText2.toString());

    // Whatever your magic formula is
    result = value1 * value2; 

    ResultField.setText(Double.toString(result));
    {// Displays result to 2 decimal places
        ResultField.setText(String.format("%1.2f", result));    
    }
}           
}