Android: external storage permission issue:

I really need someone here to guide me about some issues with the external开发者_StackOverflow storage OR sd-card. I won't go into complexities. I have a folder with the name of MyVideos. It is located in the sd-card folder of Motrola Xoom; the path is "/mnt/sdcard-ext/MyVideos. The folder is already there. However, there are some strange errors I am having.. For example, if I check if the folder exists or not using the following code:

File myDirectory = new File(defaultStorage, "/MyVideos/"); 
if (myDirectory.exists())
{  
my code: lets say true
}
else
{
my code: false
}

where defaultStorage is = "/mnt/sdcard-ext". It always return false. It should return true since the folder surely exists there. And assuming that the folder exists there, I perform other operations like

for (File f : myDirectory.listFiles()) 
    {
        if (f.isFile())
        {
            filenames.add(f.getName()); //add to array

        }//if closes
     }//for closes

I get FATAL exception at the following line

for (File f : myDirectory.listFiles())

The error stack is below:

E/AndroidRuntime(22644): FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity         
E/AndroidRuntime(22644): Caused by: java.lang.NullPointerException

I have just mentioned the things that are important from the stack. It is a NullPointerException to be precise. Although I am using

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

in my manifest file. Even then it doesn't work. The most surprising element is that it is running fine here; but there is a client in USA, it is crashing on all his devices.. Is there any difference in the permission settings of devices in UK or in USA.. I shall be thankful to you if you help me here.. It is a big problem for me. Thanks

According to the documentation, the state you're describing means that the external media storage isn't accessible to you:

public static final String MEDIA_SHARED

Added in API level 1 getExternalStorageState() returns MEDIA_SHARED if the media is present not mounted, and shared via USB mass storage.

Constant Value: "shared"

You need to go to your USB Mass Storage options and turn off USB storage.

PS : Thanks to DigCamara I copied from this SO answer.

Thanks