private void getPicFromP() {
    //通过intent去找到本机中所有属性为image的文件；
    Intent intent = new Intent();
    intent.setType("image/*");    
//ACTION_GET_CONTENT 允许用户选择特殊种类的数据，并返回，ACTION_Pick
    intent.setAction(Intent.ACTION_GET_CONTENT);
    startActivityForResult(intent,1);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    //获取到的图片为uri格式，imageView控件可以设置uri
    Uri uri = data.getData();
    Log.e("onActivityResult: ", String.valueOf(uri));
    imageView.setImageURI(uri);
}