java - 为什么我不能让这些计算显示在 TextView 上？

Question

我正在尝试制作一个使用微调器作为单位选择方法来转换距离/面积/体积的应用程序。计算意味着完成，然后根据输入到 EditText 中的内容将输出发送到 TextView 。但是输出只有 0.0，没有别的。有人可以帮忙吗？

spinner.setOnItemSelectedListener(new OnItemSelectedListener() {
        public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
            switch(pos){
            case 0:         
                option1.setAdapter(length);
                option2.setAdapter(length);
                return;
            case 1:         
                option1.setAdapter(area);
                option2.setAdapter(area);
                return;
            default:
        }           
    }

        public void onNothingSelected(AdapterView<?> parent) {
          // Do nothing.
        }
    });

    option1.setOnItemSelectedListener(new OnItemSelectedListener() {
        public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
            if(pos>=0) {
                stringInput = edittext1.getText().toString();
                if(stringInput == null || stringInput.isEmpty()) {
                    doubleInput = 0.0;
                }
                else {
                    doubleInput = Double.parseDouble(edittext1.getText().toString());
                }                                   
            }                               
        }

        public void onNothingSelected(AdapterView<?> parent) {
          // Do nothing.
        }
    });     

    option2.setOnItemSelectedListener(new OnItemSelectedListener() {
        public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
            switch(pos) {
            case 0:
                miles = doubleInput * 1;
                textview1.setText("" + String.valueOf(miles));
                return;
            case 1:
                km = doubleInput * 1.609344;
                textview1.setText("" + String.valueOf(km));
                return;
            default:
            }

        }

        public void onNothingSelected(AdapterView<?> parent) {
          // Do nothing.
        }
    });

Answer 1

冒着听起来像个老男人的风险，这看起来像是你的大学作业......是吗？

自从提出问题后，您的代码发生了变化，这使得很难回答!幸运的是，在您更改代码之前，我设法将您的代码抓取到 Eclipse 中......无论如何，在您的原始代码中，您在 create 方法中执行所有操作，此时您还没有为 edittext1 输入值(除非它被设置为一些合理的默认值，我认为它是 0，因此总是得到零作为你的答案？)

    // Whilst setting up a view the create method will not have a 
    // reasonable value for edittext1 - or it will be your default
    String stringInput = (edittext1.getText().toString());
if (stringInput.isEmpty()) { 
    doubleInput = 0.0;    // Will always enter this line
} else {
    doubleInput = Double.parseDouble(edittext1.getText().toString());
}

你复制了代码...

output1 = (TextView) findViewById(R.id.output1);

实际上 output1 到 output10(即所有十行)都是重复的。

至于您更新后的代码，它仍然给您带来问题吗？您确定 stringInput 有值吗？我的意思是你输入了什么吗？你可以通过调试你的程序来检查..

如 FloatingCoder 所建议的，以下内容也容易出错，并且可能会中断...

doubleInput = Double.parseDouble(edittext1.getText().toString());

一个更好的方法(因为它捕获了 Java 可能抛出的异常)是

doubleInput = 0.0;
String inputStr = question.getText().toString();
try {
    doubleInput = Double.parseDouble(inputStr);
} catch (NumberFormatException e) {
    // This should probably do something more useful? i.e. tell
    // the user what they've done wrong...
    Log.e("Android",
                    "Double throws a NumberFormatException if you enter text that is not a number");
}

哦，Android 有一些用于检查字符串的辅助实用程序，请参阅 TextUtils，或者只是我的示例...

if (!TextUtils.isEmpty(inputStr)) { // checks for "" and null (see documentation)
      doubleInput = Double.parseDouble(inputStr);
}

我真的建议为看起来不正确的计算编写一个简单的测试用例，因为两个文本框和一个按钮真的不难放在一起，而且非常容易调试，而不需要所有微调器都进入方式...无论如何希望这有所帮助，哦，我的完整示例有两个编辑文本和一个按钮，我将在此处发布...希望它有所帮助...

private Button btnCalc;
private EditText question, answer;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    answer = (EditText) findViewById(R.id.answer);
    question = (EditText) findViewById(R.id.question);
    btnCalc = (Button) findViewById(R.id.btnCalc);
            // The OnClickListener here will be executed outside the "Create",
            // i.e., when you actually click on the button, which will give you
            // a chance to enter some values in the question edittext...
    btnCalc.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            double in = 0.0;
            try {
                String inputStr = question.getText().toString();

                // if you want to check it use
                if (!TextUtils.isEmpty(inputStr)) {
                    in = Double.parseDouble(inputStr);
                }
            } catch (NumberFormatException e) {
                // This should probably do something more useful? i.e. tell
                // the user what they've done wrong...
                Log.e("Android",
                        "Double throws a NumberFormatException if you enter text that is not a number");
            }

            double miles = in * 1.6;
            answer.setText(String.valueOf(miles));
        }
    });
}