1.在API23+以上，不止要在AndroidManifest.xml里面添加权限

2.还要在JAVA代码中请求权限：

// 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 };

/**

* Checks if the app has permission to write to device storage

*

* If the app does not has permission then the user will be prompted to

* grant permissions

*

* @param activity

*/

public static void verifyStoragePermissions(Activity activity) {

// 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);

}

}

3.处理权限请求响应

@Override

public void onRequestPermissionsResult(int requestCode,

String permissions[], int[] grantResults) {

switch (requestCode) {

case REQUEST_EXTERNAL_STORAGE: {

// If request is cancelled, the result arrays are empty.

if (grantResults.length > 0

&& grantResults[0] == PackageManager.PERMISSION_GRANTED) {

// permission was granted, yay! Do the

// contacts-related task you need to do.

//通过时

} else {

// permission denied, boo! Disable the

// functionality that depends on this permission.

//拒绝是处理

}

return;

}

// other 'case' lines to check for other

// permissions this app might request

}

}

官方例子。

https://developer.android.com/training/permissions/requesting.html