新 android OS 5.0.1 中的文件读取错误

Question

我正在处理 android 中的文件。我使用了下面的代码，它在使用 OS 4.4.2 的注释 2 中运行良好。但是，当我在 OS 5.0.1 (Galaxy S4) 中运行时出现如下错误报告。我的代码中发生了什么？你能建议我解决它吗

private boolean checkAudioFile()
{
    ArrayList<String> datacheck=null;
    try{
    String filepath = Environment.getExternalStorageDirectory().getPath();
    String filename=filepath+"/" + FILE_FOLDER +  "/" + "file_list.txt" ;
    BufferedReader in = new BufferedReader(new FileReader(filename));
    String audio_name;
    datacheck = new ArrayList<String>();
    while ((audio_name = in.readLine()) != null) {                  
        datacheck.add(audio_name);
    }
    in.close();

    } catch (IOException e) {
        System.out.println("File Read Error");
    }
    if(datacheck.isEmpty())
        return true;
    else
        return false;
}

这是我在 OS 5.0.1

中的错误

11-16 20:42:48.483: I/System.out(16967): File Read Error
11-16 20:42:48.483: D/AndroidRuntime(16967): Shutting down VM
11-16 20:42:48.483: E/AndroidRuntime(16967): FATAL EXCEPTION: main
11-16 20:42:48.483: E/AndroidRuntime(16967): Process: com.example.readfileapp, PID: 16967
11-16 20:42:48.483: E/AndroidRuntime(16967): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.readfileapp/com.example.readfileapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.isEmpty()' on a null object reference
11-16 20:42:48.483: E/AndroidRuntime(16967):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2693)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2758)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at android.app.ActivityThread.access0(ActivityThread.java:177)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1448)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at android.os.Handler.dispatchMessage(Handler.java:102)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at android.os.Looper.loop(Looper.java:145)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at android.app.ActivityThread.main(ActivityThread.java:5942)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at java.lang.reflect.Method.invoke(Native Method)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at java.lang.reflect.Method.invoke(Method.java:372)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
11-16 20:42:48.483: E/AndroidRuntime(16967): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.isEmpty()' on a null object reference
11-16 20:42:48.483: E/AndroidRuntime(16967):    at com.example.readfileapp.MainActivity.checkAudioFile(MainActivity.java:622)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at com.example.readfileapp.MainActivity.onCreate(MainActivity.java:172)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at android.app.Activity.performCreate(Activity.java:6289)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
11-16 20:42:48.483: E/AndroidRuntime(16967):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
11-16 20:42:48.483: E/AndroidRuntime(16967):    ... 10 more

Answer 1

您需要执行空检查。

你的 ArrayList 可以是空的也可以是 null 然后你不能调用 isEmpty()

改成这样：

if(datacheck!=null && datacheck.isEmpty())

希望对您有所帮助。

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