Java Calculator android app 在计算之前或之后的任何运算符时强制关闭（需要异常处理帮助）

Question

我试图找出使用 onClick 侦听器处理异常的最佳方法。 代码中的所有内容都可以正常工作，但如果我在输入数字之前或计算之后按+, -, *, /, = ，它会使应用程序崩溃。 任何帮助，将不胜感激。 这段代码是我正在开发的多功能工具应用程序的一部分。 代码如下：

**编辑删除与错误无关的代码并添加调试输出

公共类计算器扩展片段{

    add.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            compute();
            ACTION = ADDITION;
            display.setText(String.valueOf(val1) + " + ");
            displayInfo.setText(null);
        }
    });

    sub.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            compute();
            ACTION = SUBTRACTION;
            display.setText(String.valueOf(val1) + " - ");
            displayInfo.setText(null);
        }
    });

    multiply.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            compute();
            ACTION = MULTIPLICATION;
            display.setText(String.valueOf(val1) + " * ");
            displayInfo.setText(null);
        }
    });

    divide.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            compute();
            ACTION = DIVISION;
            display.setText(String.valueOf(val1) + " / ");
            displayInfo.setText(null);
        }
    });

    equal.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
                compute();
                ACTION = EQUALS;
                display.setText(String.valueOf(val1));
                val1 = Double.NaN;
                val2 = Double.NaN;
                displayInfo.setText(null);
            }
        }
    });

}

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    return inflater.inflate(R.layout.calculator, container, false);
}

private void setupUIView(){

    zero = (Button)getView().findViewById(R.id.button_0);
    one = (Button)getView().findViewById(R.id.button_1);
    two = (Button)getView().findViewById(R.id.button_2);
    three = (Button)getView().findViewById(R.id.button_3);
    four = (Button)getView().findViewById(R.id.button_4);
    five = (Button)getView().findViewById(R.id.button_5);
    six = (Button)getView().findViewById(R.id.button_6);
    seven = (Button)getView().findViewById(R.id.button_7);
    eight = (Button)getView().findViewById(R.id.button_8);
    nine = (Button)getView().findViewById(R.id.button_9);
    decimal = (Button)getView().findViewById(R.id.button_dec);
    negate = (Button)getView().findViewById(R.id.button_neg);
    equal = (Button)getView().findViewById(R.id.button_eql);
    multiply = (Button)getView().findViewById(R.id.button_mult);
    add = (Button)getView().findViewById(R.id.button_add);
    sub = (Button)getView().findViewById(R.id.button_sub);
    divide = (Button)getView().findViewById(R.id.button_div);
    percent = (Button)getView().findViewById(R.id.button_prcnt);
    power = (Button)getView().findViewById(R.id.button_pwr);
    clear = (Button)getView().findViewById(R.id.button_clr);
    display = (TextView)getView().findViewById(R.id.display);
    displayInfo = (TextView)getView().findViewById(R.id.displayinfo);

}

private void compute(){
    if(!Double.isNaN(val1)){
        val2 = Double.parseDouble(displayInfo.getText().toString());

        switch (ACTION){
            case ADDITION:
                val1 = val1 + val2;
                break;
            case SUBTRACTION:
                val1 = val1 - val2;
                break;
            case MULTIPLICATION:
                val1 = val1 * val2;
                break;
            case DIVISION:
                val1 = val1 / val2;
                break;
            case EQUALS:

                break;

        }
    }

    else{
        val1 = Double.parseDouble(displayInfo.getText().toString());
    }
}

}

日志猫：

    Process: myapplication, PID: 29796
    java.lang.NumberFormatException: empty String
        at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1842)
        at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
        at java.lang.Double.parseDouble(Double.java:538)
        at myapplication.Calculator.compute(Calculator.java:260)
        at myapplication.Calculator.access$400(Calculator.java:19)
        at myapplication.Calculator$16.onClick(Calculator.java:187)
        at android.view.View.performClick(View.java:7870)
        at android.widget.TextView.performClick(TextView.java:14952)
        at android.view.View.performClickInternal(View.java:7839)
        at android.view.View.access$3600(View.java:886)
        at android.view.View$PerformClick.run(View.java:29315)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:237)
        at android.app.ActivityThread.main(ActivityThread.java:7762)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1047)

Answer 1

  val1 = Double.parseDouble(displayInfo.getText().toString());

这条线应该是你的第一个问题。 您正在尝试设置 val1，但 displayInfo.getText() 正在返回 "" 或 NULL。

解决问题的一种方法是使用 if 语句将所有内容包装在 onclick()-Method 中，检查 displayInfo 是否为空。 例如：

        public void onClick(View v) {
        if(!(displayInfo.getText().toString().equals(""))){
            compute();
            ACTION = DIVISION;
            display.setText(String.valueOf(val1) + " / ");
            displayInfo.setText("");
        }
    }

请注意，我用空字符串替换了 displayInfo 的文本重置，因为您试图将 null 与某个字符串连接起来，这会让您的应用程序在计算一次后崩溃。