Java Android，无效的双引号&引用；空白字段使程序崩溃

在用户输入后，我尝试使用按钮进行计算。当我没有填写字段并按下按钮时，我的程序会崩溃，但我只想发送一条消息。。我读过很多其他类似的问题，但我不明白我必须做些什么来修复我的代码。。 有人能帮我吗？？谢谢

activity_main.xml：

我得到的错误是：

谢谢

使用以下代码：

    public void calculate()
{        
        if(String.valueOf(mEditText1.getText()).length() == 0)    
        mEditText1.setError("Required only alphabets");    
        else if(String.valueOf(mEditText2.getText()).length() == 0)    
        mEditText2.setError("Required only alphabets");    
        else if(String.valueOf(mEditText3.getText()).length() == 0)
            mEditText3.setError("Required only alphabets");    
        else{
        Double value1 = Double.parseDouble(String.valueOf(mEditText1.getText()));
        Double value2 = Double.parseDouble(String.valueOf(mEditText2.getText()));
        Double value3 =    Double.parseDouble(String.valueOf(mEditText3.getText()));
        calculatedValue = (value2 * value3) / value1;
        mTextView.setText(calculatedValue.toString());
       }
 }  

---

实现尝试。。。抓住。。从哪里可以找到crashWonder为什么

“

不能被视为有效数字？因为Java不会将

“

转换为

0

。Double value1=Double.parseDouble（String.valueOf（mEditText1.getText（））；Double value2=Double.parseDouble（String.valueOf（mEditText2.getText（））；Double value3=Double.parseDouble（String.valueOf（mEditText3.getText（））；你知道这会导致完全相同的异常，对吗？这里的问题是解析double。在解析之前，您必须检查输入是否正确，@0xDEADC0DE，谢谢您的通知，它工作正常！！非常感谢！！！：）

......
mEditText1 = (EditText)findViewById(R.id.editText1);
mEditText2 = (EditText)findViewById(R.id.editText2);
mEditText3 = (EditText)findViewById(R.id.editText3);
mTextView = (TextView)findViewById(R.id.textView1);
cButton =  (Button)findViewById(R.id.calculateButton);
    cButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            //When the button is clicked, call the calucate method.
            calculate();
        }
    });

......

public void calculate(){

    Double value1 = Double.parseDouble(mEditText1.getText().toString());
    Double value2 = Double.parseDouble(mEditText2.getText().toString());
    Double value3 = Double.parseDouble(mEditText3.getText().toString());
    if((value1!=0)&&(value2!=0)) {

        if ((value1 != null) && (value2 != null) && (value3 != null)) {
            calculatedValue = (value2 * value3) / value1;
            mTextView.setText(calculatedValue.toString());}
    else {
            Toast.makeText(getApplicationContext(), "Please fill them all", Toast.LENGTH_LONG).show();
          }
 }

12-22 20:09:26.694 18523-18523/com.example.nigi.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
    java.lang.NumberFormatException: Invalid double: ""
    at java.lang.StringToReal.invalidReal(StringToReal.java:63)
    at java.lang.StringToReal.parseDouble(StringToReal.java:248)
    at java.lang.Double.parseDouble(Double.java:295)
    at android.view.View.performClick(View.java:4442)
    at android.view.View$PerformClick.run(View.java:18473)
    at android.os.Handler.handleCallback(Handler.java:733)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:136)
    at android.app.ActivityThread.main(ActivityThread.java:5105)

    public void calculate()
{        
        if(String.valueOf(mEditText1.getText()).length() == 0)    
        mEditText1.setError("Required only alphabets");    
        else if(String.valueOf(mEditText2.getText()).length() == 0)    
        mEditText2.setError("Required only alphabets");    
        else if(String.valueOf(mEditText3.getText()).length() == 0)
            mEditText3.setError("Required only alphabets");    
        else{
        Double value1 = Double.parseDouble(String.valueOf(mEditText1.getText()));
        Double value2 = Double.parseDouble(String.valueOf(mEditText2.getText()));
        Double value3 =    Double.parseDouble(String.valueOf(mEditText3.getText()));
        calculatedValue = (value2 * value3) / value1;
        mTextView.setText(calculatedValue.toString());
       }
 }