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在 while 语句中， final2.add(read) 得到一个空指针，这让我相信它没有正确读取文件，所以我的问题是以下我是否正确获取了文本文件的内容？

@SuppressWarnings("null")
public void loadOpp() throws FileNotFoundException {
    File y = new File(getFilesDir()+File.separator+"Opponent.txt");
    FileReader x = new FileReader(y);
    BufferedReader bufferedReader = new BufferedReader(x);
    String read;

    List<String> final2 = new ArrayList();               
    try {
        while((read = bufferedReader.readLine()) != null){
            final2.add(read);
          }
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    Spinner spinner= (Spinner) findViewById(R.id.spinner3);
    ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_spinner_item, final2);
    dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinner.setAdapter(dataAdapter);        
}

日志猫：

09-06 21:43:00.874: E/AndroidRuntime(779): FATAL EXCEPTION: main
09-06 21:43:00.874: E/AndroidRuntime(779): java.lang.RuntimeException: Unable to start activity     ComponentInfo{com.example.hoopstats/com.example.hoopstats.NewGame}: java.lang.NullPointerException
09-06 21:43:00.874: E/AndroidRuntime(779):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
09-06 21:43:00.874: E/AndroidRuntime(779):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
09-06 21:43:00.874: E/AndroidRuntime(779):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
09-06 21:43:00.874: E/AndroidRuntime(779):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
09-06 21:43:00.874: E/AndroidRuntime(779):  at android.os.Handler.dispatchMessage(Handler.java:99)
09-06 21:43:00.874: E/AndroidRuntime(779):  at android.os.Looper.loop(Looper.java:137)
09-06 21:43:00.874: E/AndroidRuntime(779):  at android.app.ActivityThread.main(ActivityThread.java:5103)
09-06 21:43:00.874: E/AndroidRuntime(779):  at java.lang.reflect.Method.invokeNative(Native Method)
09-06 21:43:00.874: E/AndroidRuntime(779):  at java.lang.reflect.Method.invoke(Method.java:525)
09-06 21:43:00.874: E/AndroidRuntime(779):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-06 21:43:00.874: E/AndroidRuntime(779):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-06 21:43:00.874: E/AndroidRuntime(779):  at dalvik.system.NativeStart.main(Native Method)
09-06 21:43:00.874: E/AndroidRuntime(779): Caused by: java.lang.NullPointerException
09-06 21:43:00.874: E/AndroidRuntime(779):  at com.example.hoopstats.NewGame.loadOpp(NewGame.java:67)
09-06 21:43:00.874: E/AndroidRuntime(779):  at com.example.hoopstats.NewGame.onCreate(NewGame.java:34)
09-06 21:43:00.874: E/AndroidRuntime(779):  at android.app.Activity.performCreate(Activity.java:5133)
09-06 21:43:00.874: E/AndroidRuntime(779):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
09-06 21:43:00.874: E/AndroidRuntime(779):  at     android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
09-06 21:43:00.874: E/AndroidRuntime(779):  ... 11 more
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1 回答 1

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请参阅Android 文档

在您说“final2.add(read)”得到一个空指针的问题中，您确定是这种情况吗？堆栈跟踪显示的内容并不完全如此。我认为这条线

((read = bufferedReader.readLine()) != null)

确保不会出现这种情况。该语句将被评估如下

read = bufferedReader.readLine();

从文档中，这将返回“该行的内容，如果在到达阅读器末尾之前没有读取任何字符，则返回 null。”

(expression) != null

然后将该表达式的结果与 null 进行比较，因此您的代码不应将 null 添加到 final2。

我认为您的问题更有可能是“findViewById”可能返回 null - 再次检查广泛的在线文档。我还将删除 SuppressWarnings("null") 属性

您的代码可能在其他地方出错。如果有疑问，在整个方法中添加 Log.d() 并查看 logcat 中出现了什么...或调试该方法...至少记录正在读取的行，直到您确定您的数据已被正确读取.

这就是我认为您的代码应该这样读的方式（未经测试）...

public void loadOpp() {

    // Consider openFileInput(OPPONENT_FILE) instead of the following...
    File opponentFile = new File(getFilesDir(), OPPONENT_FILENAME);
    if (opponentFile.exists()) { // check the file exists
        FileReader reader = new FileReader(opponentFile);
        BufferedReader bufferedReader = new BufferedReader(reader);

        List<String> opponentList = new ArrayList<String>();

        String line = null;
        while ((line = bufferedReader.readLine()) != null) {

            // Attempt some logging (exercise for the reader)
            Log.d(this.getClass().getName(), line);

            opponentList.add(line);
        }

        Spinner spinner = (Spinner) findViewById(R.id.spinner3);
        if (spinner != null) {
            ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this,
                    android.R.layout.simple_spinner_item, opponentList);
            dataAdapter
                    .setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            spinner.setAdapter(dataAdapter);
        }
    }
}

其他要检查的事情，您的文件是否存在？它是否包含任何数据？请记住，如果您正在创建文件，则应在创建文件之前检查设备上是否有可用空间......等等......

希望有帮助。

于 2013-09-08T03:00:55.260 回答