Question

我想在RatingBar的帮助下找到用户选择的一系列值的平均值。每次用户按下Button时，我都想将RatingBar的值写入文件。但是当我尝试保存该值时，新值将覆盖文件中的旧值而不是附加值。我宁愿将文件保存在内部存储器中。

之后，我想获取所有值并将它们放入ArrayList。并计算所有给定值的平均值。

我是从C＃开始的，所以WriteLine()和ReadLine()很容易，但writeline不存在（至少，我没有在我的研究中找到）和某些情况，readline已被弃用。

我试着这样做：

 private void writeMyArray(double rate){
    try{
        FileWriter fileWritter = new FileWriter("test3",true);
        BufferedWriter bufferWritter = new BufferedWriter(fileWritter);
        bufferWritter.write(Double.toString(rate));
        bufferWritter.close();

    }catch(IOException e){
        e.printStackTrace();
    }

private void readMyArray(ArrayList<String> list){
    try {
        InputStream inputStream = openFileInput("test3.txt");
        InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
        BufferedReader reader = new BufferedReader(inputStreamReader);
        while (true) {
            String line = reader.readLine();
            if (line == null) {
                list.add("");
                break;
            }
            list.add(line);
        }
        reader.close();

} catch (FileNotFoundException e) {
        e.printStackTrace();
    }
    catch (IOException e) {
        e.printStackTrace();
    }
}

当我按下按钮时，使用以下代码：

button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            rating = ratingbar.getRating();
            writeToFile(Double.toString(rating));
            writeMyArray(ratingbar.getRating());

            button.setText(getText(R.string.obrigado) + "!" + readFromFile() + arraydays.get(0));// + media(Double.parseDouble(readMyArray()), Integer.parseInt(stackread())));
            //button.setText(getText(R.string.obrigado)+"!");
            //ratingbar.setEnabled(false);
           // button.setEnabled(false);
        }
    });

我收到此logcat错误：

07-06 10:54:44.180  29840-29840/com.example.emilio.notification E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.emilio.notification, PID: 29840
java.lang.IndexOutOfBoundsException: Invalid index 0, size is 0
        at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255)
        at java.util.ArrayList.get(ArrayList.java:308)
        at com.example.emilio.notification.MainActivity$2.onClick(MainActivity.java:116)
        at android.view.View.performClick(View.java:4780)
        at android.view.View$PerformClick.run(View.java:19866)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5257)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

写/读文件方法用于其他目的但工作正常，因此问题在于我的数组代码。

其他文件代码

private void writeToFile(String data) {
    try {
        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(openFileOutput("estrela.txt", Context.MODE_PRIVATE));
        outputStreamWriter.write(data);
        outputStreamWriter.close();

    } catch (IOException e) {
        Log.e("Exception", "File write failed: " + e.toString());
    }
}


private String readFromFile() {

    String ret = "";

    try {
        InputStream inputStream = openFileInput("estrela.txt");

        if (inputStream != null) {
            InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
            BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
            String receiveString = "";
            StringBuilder stringBuilder = new StringBuilder();

            while ((receiveString = bufferedReader.readLine()) != null) {
                stringBuilder.append(receiveString);
            }

            inputStream.close();
            ret = stringBuilder.toString();
        }
    } catch (FileNotFoundException e) {
        Log.e("login activity", "File not found: " + e.toString());
    } catch (IOException e) {
        Log.e("login activity", "Can not read file: " + e.toString());
    }

    return ret;
}

Answer 1

我假设你在这里寻找三种方法。一个将double附加到文件，另一个将数字读取到ArrayList<Double>，第三个计算平均评分。

写：

public void writeToFile(double rate) throws IOException {
    FileOutputStream fout;
    fout = new FileOutPutStream("myfile.txt", true);
    new PrintStream(fout).println(rate);
    fout.close();
}

读：

public List<Double> readFromFile() throws IOException {
    List<Double> rateList = new ArrayList<Double>();
    Scanner s = new Scanner(new FileInputStream("myfile.txt"), "utf-8");
    while (s.hasNextLine()) {
        rateList.add(Double.parseDouble(s.nextLine()));
    }
    return rateList;
}

查找平均评分：

public double findAverageRating(List<Double> rateList) {
    double averageRating = 0;
    for (double r : rateList)
        averageRating += r;
    return averageRating / rateList.size();
}

这意味着您可以在按钮侦听器中执行以下操作：

writeToFile(ratingbar.getRating());
button.setText(findAverageRating(readFromFile()));

Answer 2

你的Logcat输出已经告诉你，出了什么问题。您拨打arraydays.get(0)，而 arraydays 似乎的大小为0，但您正试图从中获取第一个值。您将使用list.add(line)附加到名为 list 的变量。这就是我所理解的。你的代码是不可读的。

Android：如何写入文件并在之后将其读入数组

2 个答案: