如何計算Android中的EditText值？

Question

在Android應用程序中，我使用兩個EditText控件並將它們的兩個值相乘。 如果其中一個EditText是null，並且在第二個中我提出了一個值，它不能正常工作。 我該如何處理這種情況，其中我在另一個EditText和null中有一個值，我想將這兩個值相乘？

Answer 1

首先，你需要有關於何時執行計算的觸發器。說這是一個按鈕，或者，甚至更好，每一次你EditText變遷之一的值：

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()); 
} 

Answer 2

在按鈕單擊它們是否是空的，或者不是相乘的EditText箱2點的值，並檢查：

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())));  
     } 
    }); 
} 

Answer 3

@luvieere代碼的輕微變化：

//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));  
    } 
}   
}