android6.0 讀取storage文件夾需要手動檢測讀取權限

解決方案摘自： 

http://stackoverflow.com/questions/8854359/exception-open-failed-eacces-permission-denied-on-android

除了在AndroidManifest.xml中申請權限

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

還需要在讀寫文件中設置一下代碼：

// Storage Permissions
private static final int REQUEST_EXTERNAL_STORAGE = 1;
private static String[] PERMISSIONS_STORAGE = {
        Manifest.permission.READ_EXTERNAL_STORAGE,
        Manifest.permission.WRITE_EXTERNAL_STORAGE
};

// Check if we have write permission
int permission = ActivityCompat.checkSelfPermission(activity, Manifest.permission.WRITE_EXTERNAL_STORAGE);
if (permission != PackageManager.PERMISSION_GRANTED) {
   // We don't have permission so prompt the user
   ActivityCompat.requestPermissions(
       activity,
       PERMISSIONS_STORAGE,
       REQUEST_EXTERNAL_STORAGE
     );
 }