android - 如何计算 Android 中的 EditText 值？

Question

在 Android 应用程序中，我使用了两个 EditText 控件并将它们的两个值相乘。如果一个 EditText 是 null 而在第二个中我输入了一个值，它就无法正常工作。我该如何处理这种情况，我在一个 EditText 中有一个值，在另一个中有一个 null，我想将这两个值相乘？

Answer 1

首先，您需要有一个触发器来确定何时执行计算。假设它是一个按钮，或者更好的是，每当您的 EditText 之一的值发生变化时:

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());
}