检查editText是否为空

Question

我有一个editText（称为输入），用户在其中输入一个值，然后选择一个单选按钮以将该值转换为其他度量单位。 我正在尝试建立一个if语句，以便在未选择单选按钮且edittext为空的情况下显示一条文本消息，但它始终使程序崩溃！

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) { 

任何想法是什么导致程序崩溃？

编辑：这是日志：

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)

Answer 1

问题是这行代码：

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

您传递了一个空String，并导致出现NumberFormatException，就像您的情况一样。

使用该代码使其更具可读性：

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) { 

Answer 2

您的String为空，因此在尝试解析它时会出错。 检查字符串是否为空

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

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

或捕获NumberFormatException

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

Answer 3

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) {