检查editText是否为空

我有一个editText（称为输入），其中用户输入一个值，然后选择一个单选按钮将该值转换为不同的度量单位。我正在尝试设置一个if语句，以便在未选中单选按钮并且edittext为空的情况下显示一条文本消息，但它会使程序崩溃！检查editText是否为空

public void startCalculation() { 
    RadioGroup rg = (RadioGroup)findViewById(R.id.radioGroup); 
    int selectedConversion = rg.getCheckedRadioButtonId(); 
    double input = Double.parseDouble(((EditText) findViewById(R.id.currentSpeed)).getText().toString()); 
    double speed = 0; 
    String measurement = ""; 
    System.out.println("The Value of Input is: " + input); 

    //If its 0 then no unit has been selected 
    if(selectedConversion != -1 && input > 0) {

任何想法什么导致程序崩溃？

编辑：下面是日志：

10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime: FATAL EXCEPTION: main 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime: Process: com.example.dan14.windproject, PID: 2058 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime: java.lang.NumberFormatException: Invalid double: "" 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at java.lang.StringToReal.invalidReal(StringToReal.java:63) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at java.lang.StringToReal.parseDouble(StringToReal.java:267) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at java.lang.Double.parseDouble(Double.java:301) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at com.example.dan14.windproject.MainActivity.startCalculation(MainActivity.java:88) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at com.example.dan14.windproject.MainActivity$2.onClick(MainActivity.java:49) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at android.view.View.performClick(View.java:5198) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at android.view.View$PerformClick.run(View.java:21147) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at android.os.Handler.handleCallback(Handler.java:739) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at android.os.Handler.dispatchMessage(Handler.java:95) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at android.os.Looper.loop(Looper.java:148) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at android.app.ActivityThread.main(ActivityThread.java:5417) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at java.lang.reflect.Method.invoke(Native Method) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
10-27 13:39:02.357 2058-2058/com.example.dan14.windproject E/AndroidRuntime:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

来源

2015-10-27 Haldamir

什么是errormessage的？请向我们展示onCreate方法。顺便说一下， –

和日志请 – AsfK

。如果您的editText为空，则必须导致NumberFormatException –

问题是这行代码：

double input = Double.parseDouble(((EditText) findViewById(R.id.currentSpeed)).getText().toString());

你传递一个空字符串，并导致一个NumberFormatException的像你的情况。

使其与代码更易读：

public void startCalculation() { 
    RadioGroup rg = (RadioGroup)findViewById(R.id.radioGroup); 
    int selectedConversion = rg.getCheckedRadioButtonId(); 
    String lInputString = ((EditText) findViewById(R.id.currentSpeed)).getText().toString(); 
    double input = 0; 
    if (!lInputString.trim().equals("")){ 
     input = Double.parseDouble(lInputString); 
    } 
    double speed = 0; 
    String measurement = ""; 
    System.out.println("The Value of Input is: " + input); 

    //If its 0 then no unit has been selected 
    if(selectedConversion != -1 && input > 0) {

来源

2015-10-27 13:41:55

啊！好。那么我如何在if语句中通过这个呢？ – Haldamir

看到我更新的答案。 –

完美地工作！谢谢！ – Haldamir

你String是空的，所以当你尝试分析它有一个错误。检查字符串不是空

String text = ((EditText) findViewById(R.id.currentSpeed)).getText().toString(); 

if(!text.isEmpty()) { 
    double input = Double.parseDouble(text); 
}

或捕捉NumberFormatException的

try { 
    double input = Double.parseDouble(((EditText) findViewById(R.id.currentSpeed)).getText().toString()); 
} catch(NumberFormatException e) { 
    //Error during parse 
}

来源

2015-10-27 13:45:51 ThomasThiebaud

public void startCalculation() { 
RadioGroup rg = (RadioGroup)findViewById(R.id.radioGroup); 
int selectedConversion = rg.getCheckedRadioButtonId(); 
try{ 
double input = Double.parseDouble(((EditText) findViewById(R.id.currentSpeed)).getText().toString()); 
}catch(Exception e) 
{ 
//if catch block is execute it means edittext is empty 
} 
double speed = 0; 
String measurement = ""; 
System.out.println("The Value of Input is: " + input); 

//If its 0 then no unit has been selected 
if(selectedConversion != -1 && input > 0) {

来源

2015-10-27 13:57:20

看到try catch块，如果edittext null，那么你可以在catch块中编写代码 –

检查editText是否为空

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