Android 应用程序在尝试从编辑文本中获取值并变成双精度时崩溃

Question

我是Android Studio的新手，Java对我来说很新。我正在尝试制作一个转换应用程序。 为此，我必须获取编辑文本框的值并将其转换为数字。那是我的应用程序崩溃的时候，我添加的那一刻：

double n1Var = Double.parseDouble(n1.getText().toString());

我的应用将打开，然后立即关闭。如果我删除它，该应用程序可以正常工作。我尝试了不同的方法将其变成双精度，尝试将其转换为整数仍然不起作用。如果我尝试一个字符串，它可以正常工作。

Answer 1

//assuming that (EditText)n1 = (EditText)findViewById(R.id.id_of_n1);
String et_val = n1.getText().toString().trim();
double n1Var;
if(et_val.equals("") || et_val.length==0 ){
/*you can improve on this filter with a regex to check if the content of the edit text is event a number. 
Furthermore, you can also control the entry of the information allowed into edit text with a switch in the xml for the edit text by allowing for only entry of numbers.
You can also do control the entry into the edit text with a java code that would compel the user to only enter numbers if that complies with what you are looking forward to executing with the user.
*/ 
    n1Var = 0;
}else{
    n1Var = Double.parseDouble(et_val);
}

希望这有帮助。干杯和快乐编码。

Answer 2

似乎

没有任何效果.这是我的代码+当我按下按钮打开双精度的活动时的日志......

日志屏幕截图

EditText ETInput;
Button BConvert;
TextView TVresult;
RadioButton c2f;
RadioButton c2k;
RadioButton f2c;
RadioButton f2k;
RadioButton k2c;
RadioButton k2f;
@RequiresApi(api = Build.VERSION_CODES.N)
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_converter);

   ETInput = (EditText)findViewById(R.id.ETInput);
    double a = Double.parseDouble(ETInput.getText().toString());
   BConvert = (Button)findViewById(R.id.BConvert);
   TVresult = (TextView)findViewById(R.id.TVresult);
   c2f = (RadioButton)findViewById(R.id.c2f);
   c2k = (RadioButton)findViewById(R.id.c2k);
   f2c = (RadioButton)findViewById(R.id.f2c);
    f2k = (RadioButton)findViewById(R.id.f2k);
    k2c = (RadioButton)findViewById(R.id.k2c);
    k2f = (RadioButton)findViewById(R.id.k2f);


    String val = ETInput.getText().toString().trim();
    double var;
    var = Double.parseDouble(val);


}

}

Answer 3

with this：

双W;

    try {
        w = new Double(input.getText().toString());
    } catch (NumberFormatException e) {
        w = 0;
    }

w 始终为零

Answer 4

从 Java 文档中，以下是可以从Double.parseDouble抛出的异常：

抛出：

空指针异常 - 如果字符串为空

NumberFormatException - 如果字符串不包含可解析的双精度。

从你的描述来看，很可能NullPointerException被扔了。检查日志猫以准确找出抛出的异常。