安卓:我不能在GridView上显示手机的图片

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

if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, REQUEST_CODE);
}

String[] projection = {MediaStore.Images.Media.DATA};
Cursor cursor = getContentResolver().query(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, projection, null, null, null);
ArrayList<String> imagePathList = new ArrayList<>();
if (cursor != null) {
    int columnIndex = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
    while (cursor.moveToNext()) {
        String imagePath = cursor.getString(columnIndex);
        imagePathList.add(imagePath);
    }
    cursor.close();
}