Question

我试图在nexus7中列出sdcard中的所有文件，但我得到了nullpointer异常。

以下代码在三星tab2中运行正常，但在nexus7中出现问题。

如果有人有想法，请帮助我。

    ArrayList<String> listFolders = new ArrayList<String>();
    ArrayList<String> listFiles = new ArrayList<String>();
    String globalPath = "";




     public void onClikButton(View v) {
            String path = Environment.getExternalStorageDirectory()+"/";

        getDirectory(path);
    }


    public void getDirectory(String path) {
        //String setPath = path;
        globalPath = path;
        Log.i("getDirectory","globalPath = " + globalPath);

        String[] splitPath = path.split("/");
        int count = splitPath.length;
        Log.i("getDirectory","globalPath count = " + count);
        if(count==3)
        {
            // Root
            btnBack.setVisibility(View.GONE);
        }
        else
        {
            btnBack.setVisibility(View.VISIBLE);
        }

        File directory = new File(globalPath);
        File[] listDirectory =null;

        if(directory.exists()) {
                  listDirectory = directory.listFiles();
       for(int i=0; i<listDirectory.length;i++)
        {
        File getFolder = listDirectory[i];
        if(getFolder.isDirectory())
        {
            listFolders.add(getFolder.getName());
        }
       }
    }
     }

日志： -

12-26 15:49:53.390: E/(6322): results[0]: 3839
12-26 15:49:53.390: E/(6322): results[1]: 3839
12-26 15:49:53.390: E/(6322): results[2]: 0
12-26 15:49:53.390: E/(6322): results[3]: 0
12-26 15:49:53.590: E/AndroidRuntime(6322): FATAL EXCEPTION: main
12-26 15:49:53.590: E/AndroidRuntime(6322): Process: com.allappsmobile.pdfsdk.app, PID: 6322
12-26 15:49:53.590: E/AndroidRuntime(6322): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.allappsmobile.pdfsdk.app/com.allappsmobile.pdfsdk.app.ActivityDirectory}: java.lang.NullPointerException
12-26 15:49:53.590: E/AndroidRuntime(6322):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at android.os.Handler.dispatchMessage(Handler.java:102)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at android.os.Looper.loop(Looper.java:136)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at android.app.ActivityThread.main(ActivityThread.java:5017)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at java.lang.reflect.Method.invokeNative(Native Method)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at java.lang.reflect.Method.invoke(Method.java:515)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at dalvik.system.NativeStart.main(Native Method)
12-26 15:49:53.590: E/AndroidRuntime(6322): Caused by: java.lang.NullPointerException
12-26 15:49:53.590: E/AndroidRuntime(6322):     at com.allappsmobile.pdfsdk.app.ActivityDirectory.getDirectory(ActivityDirectory.java:89)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at com.allappsmobile.pdfsdk.app.ActivityDirectory.onCreate(ActivityDirectory.java:47)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at android.app.Activity.performCreate(Activity.java:5231)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
12-26 15:49:53.590: E/AndroidRuntime(6322):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
12-26 15:49:53.590: E/AndroidRuntime(6322):     ... 11 more

提前致谢!!

Answer 1

替换

String path = Environment.getExternalStorageDirectory()+"/";

带

Environment.getExternalStorageDirectory().getAbsolutePath()

Answer 2

用这个

替换你的onClickButton（）

public void onClikButton(View v) {
        String path = Environment.getExternalStorageDirectory().getAbsolutePath();

    getDirectory(path);
}

Answer 3

执行以下操作：

替换

String path = Environment.getExternalStorageDirectory()+"/";

带

Environment.getExternalStorageDirectory()

替换

if(count==3)

与

if(path.equals(Environment.getExternalStorageDirectory().getAbsolutPath()))

Answer 4

我在堆栈溢出时发现这个...可能有帮助..

似乎是known issue affecting Android USB file access over MTP。在重新启动手机之前，MTP缓存已过期。

解决方法是：

清除“媒体存储”应用的数据
使用SDrescan应用强制更新。

或者完全避免使用USB。问题不会影响其他访问文件的方法。例如，尝试AirDroid传输文件。

/ storage / emulated / legacy

/ mnt / shell / emulated / 0

从sdcard列出文件和目录时出现NullpointerException

4 个答案: