Question

我有这个代码在原始文件夹中的txt文件中写入一个双数字，另一个用于读取文件并将所有双数字放在数组中。我使用数组来平均文件中的双数。（双倍是我的ratingbar double）在读取之后，在OnClickListener按钮中调用write。

（有人可以编辑这个，我通常不会用英文写，所以我确定它会有一些错误，即使在这个引用中也可能）

写：

private void writeMyArray(double rate){
        //PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("arraymedia.txt", true)));
        //.println(rate);
        double ratex2 = rate * 2;
        int erate = (int)ratex2;
            try
            {
                OutputStreamWriter outputStreamWriter = new OutputStreamWriter(openFileOutput("myarray.txt", Context.MODE_APPEND));
                outputStreamWriter.append(Integer.toString(erate));
                outputStreamWriter.close();
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

}

读：

private void readMyArray(ArrayList<Double>array){

    String ret = "";


            try {
                InputStream inputStream = this.getResources().openRawResource(R.raw.myarray);

                if (inputStream != null) {
                    InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
                    BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
                    String receiveString = "";
                    StringBuilder stringBuilder = new StringBuilder();
                    int enc = 0;
                    while ((receiveString = bufferedReader.readLine()) != null) {
                        stringBuilder.append(receiveString);
                        array.set(enc, Double.parseDouble(bufferedReader.readLine()));
                        ++enc;
                    }
                    inputStream.close();
            }
        } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
}

平均

private double media(ArrayList<Double>array)
{
    double total = 0;
    double media;
    int a = 0;
    for (int i=0; i<array.size(); i++)
    {
        total = total + array.get(i);
        a=i;
    }
    media = total / a;
    return media;
}

logcat中的错误

07-03 09:55:14.496  17307-17307/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.emilio.notification, PID: 17307
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object java.util.ArrayList.set(int, java.lang.Object)' on a null object reference
        at com.example.emilio.notification.MainActivity.readMyArray(MainActivity.java:210)
        at com.example.emilio.notification.MainActivity.access$200(MainActivity.java:45)
        at com.example.emilio.notification.MainActivity$2.onClick(MainActivity.java:111)
        at android.view.View.performClick(View.java:4780)
        at android.view.View$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)

按钮点击代码

button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            ratingbar.setEnabled(false);
            rating = ratingbar.getRating();

           writeMyArray(rating);
            readMyArray(arraydays);
            button.setText(getText(R.string.obrigado) + "!" + media(arraydays));
            //button.setText(getText(R.string.obrigado)+"!");

            button.setEnabled(false);
        }
    });

UPTADE

当我更改array.set（）时，它给了我这个错误：

07-03 10:25:53.576  25334-25334/com.example.emilio.notification E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.emilio.notification, PID: 25334
java.lang.IndexOutOfBoundsException: Invalid index 0, size is 0
        at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255)
        at java.util.ArrayList.set(ArrayList.java:481)
        at com.example.emilio.notification.MainActivity.readMyArray(MainActivity.java:210)
        at com.example.emilio.notification.MainActivity.access$200(MainActivity.java:45)
        at com.example.emilio.notification.MainActivity$2.onClick(MainActivity.java:111)
        at android.view.View.performClick(View.java:4780)
        at android.view.View$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)

Answer 1

问题在于你的while循环

while(receiveString = bufferedReader.readLine()) != null)

这很好，因为它会检查null。

但是在你的循环中，你会再次获得bufferedReader.readLine()。

所以这意味着，当循环位于最后string而非null时。

代码将接收下一个string，现在等于null。

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

    // The next line is the problem
    // bufferedReader.readline() is either null
    // or array is null

    // bufferedReader.readLine() is going to be set to null on the last run.
    array.set(enc, Double.parseDouble(bufferedReader.readLine()));

    ++enc;
}

我想你可能正在寻找这个

array.set(enc, Double.parseDouble(receiveString));

或可能

string doubleToParse = bufferedReader.readLine();
if(doubleToParse != null) {
    array.set(enc, doubleToParse);
}

注意：
在第二个答案中，每次通过循环时，您将从bufferedReader获取两行。

您可能面临的下一个问题是设置ArrayList。

确保您已经打过电话

ArrayList<Double> arrayDays = new ArrayList<Double>();

如果你还没有填充数组。你应该打电话：

array.add(Double.parseDouble(doubleToParse));

最后一点，您必须确定您要解析的每个字符串实际上都包含Double。

否则您将面临java.lang.NumberFormatException。

try {
    Double d = Double.parseDouble(doubleToParse);
    array.add(d);
} catch (NumberFormatException ex) {
    System.out.println(ex.getMessage());
}

Answer 2

代码似乎很好，尝试替换

InputStream inputStream = this.getResources().openRawResource(R.raw.myarray);

到

InputStream inputStream = MainActivity.this.getResources().openRawResource(R.raw.myarray);

应该适合你。

写入ArrayList时出现空指针异常

2 个答案: