Question

我正在制作一个简单的货币计算器用于学习目的，我不知道为什么我的代码不会起作用。目前，当我按下＆＃34;转换＆＃34;按钮有一条消息说＆＃34; Appname停止工作＆＃34;

以下是代码：

public class MainActivity extends AppCompatActivity {

    //Button convertButton;



    public void  convert(View view) {

        EditText dkk = (EditText) findViewById(R.id.dkkField);
        EditText gbp = (EditText) findViewById(R.id.gbpField);
        EditText eur = (EditText) findViewById(R.id.eurField);
        EditText usd = (EditText) findViewById(R.id.usdField);


        Double dkkNum = Double.parseDouble(dkk.getText().toString());
        Double gbpNum = Double.parseDouble(gbp.getText().toString());
        Double eurNum = Double.parseDouble(eur.getText().toString());
        Double usdNum = Double.parseDouble(usd.getText().toString());

        TextView textView = (TextView) findViewById(R.id.resultView);


        double dkkTogbp;
        double dkkToeur;
        double dkkTousd;
        double gbpToDkk;
        double eurToDkk;
        double usdToDkk;


        if(dkk!=null){

            dkkTogbp = dkkNum * 0.114001;
            dkkToeur = dkkNum * 0.134489;
            dkkTousd = dkkNum * 0.142729;

            textView.setText(dkk+ "DKK is "+ dkkTogbp+" GBP, "+dkkToeur+"EUR, "+ dkkTousd +"USD");


        }else if(gbp!=null){

            gbpToDkk = gbpNum * 8.77189;

            textView.setText(dkk+ "GBP is "+ gbpToDkk+" DKK");


        }else if(eur!=null){

            eurToDkk = eurNum * 7.43555;

            textView.setText(dkk+ "EUR is "+ eurToDkk+" DKK");

        }else if(usd!=null){

            usdToDkk = usdNum * 7.00630;

            textView.setText(dkk+ "USD is "+ usdToDkk+" DKK");
            Toast.makeText(getApplicationContext(), dkk.toString() + " DKK", Toast.LENGTH_LONG).show();

        }


        dkk.setText("");
        gbp.setText("");
        eur.setText("");
        usd.setText("");

    }

我发现当我删除下面的代码块和if语句时程序可以运行而不会崩溃：

 Double dkkNum = Double.parseDouble(dkk.getText().toString());
        Double gbpNum = Double.parseDouble(gbp.getText().toString());
        Double eurNum = Double.parseDouble(eur.getText().toString());
        Double usdNum = Double.parseDouble(usd.getText().toString());

有人可以解释为什么会这样吗？

我没有收到任何错误。

Answer 1

问题在于将文本解析为double值。

首先，您应该使用try-catch块来保存应用程序崩溃，如下所示：

        try
        {
            Double dkkNum = Double.parseDouble(dkk.getText().toString());
            Double gbpNum = Double.parseDouble(gbp.getText().toString());
            Double eurNum = Double.parseDouble(eur.getText().toString());
            Double usdNum = Double.parseDouble(usd.getText().toString());
        }
        catch(NumberFormatException ex)
        {
            // If the format of the input string is wrong, then you get here the error message
        }
        catch(NullPointerException ex)
        {
            // If the input string is null, then you get here the error message
        }

检查应该解析的文本是否具有正确的语法，如“1.9”。

更新：如果输入字符串为null，则“parseDouble”方法抛出“NullPointerException”。有关更多信息，请参阅this link。我已经更新了代码。

代码因未知原因导致我的应用程序崩溃

1 个答案: