Material File Picker 
Material file picker library for Android
Using
Add repository url and dependency in application module gradle file:
repositories {
maven {
url "http://dl.bintray.com/lukaville/maven"
}
}
dependencies {
compile 'com.nbsp:library:1.8'
}
Open file picker:
new MaterialFilePicker()
.withActivity(this)
.withRequestCode(1)
.withFilter(Pattern.compile(".*\\.txt$")) // Filtering files and directories by file name using regexp
.withFilterDirectories(true) // Set directories filterable (false by default)
.withHiddenFiles(true) // Show hidden files and folders
.start();
or
Intent intent = new Intent(this, FilePickerActivity.class);
intent.putExtra(FilePickerActivity.ARG_FILE_FILTER, Pattern.compile(".*\\.txt$"));
intent.putExtra(FilePickerActivity.ARG_DIRECTORIES_FILTER, true);
intent.putExtra(FilePickerActivity.ARG_SHOW_HIDDEN, true);
startActivityForResult(intent, 1);
Override on activity result:
@Override protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == 1 && resultCode == RESULT_OK) {
String filePath = data.getStringExtra(FilePickerActivity.RESULT_FILE_PATH);
// Do anything with file
}
}
Runtime permissions:
You should handle runtime permissions in activity, from what you called Material File Picker. Look here for example code.