OnScrollChanged 没有获取 RecyclerView 参数

Question

我正在尝试在我的项目中实施 this code：

不同之处在于，我使用的是 RecyclerView 而不是 ScrollView 而不是直接在 Activity 中使用我的 RecyclerView 我在里面使用了一个设置我需要的侦听器的片段。问题是，虽然 OnScrollChanged(int l, int t, int oldl, int oldt) 实际上在我每次滚动时都会被调用，但它获得的参数始终为 0，我不明白为什么，所以 ScrollChangedTarget 没有按预期工作。

这是自定义 RecyclerView：

 public class NotifyingScrollRecyclerView : RecyclerView
{
    private Activity activity;
    private View headerView;
    private View footerView;

    public delegate void ScrollChangedHandler(int l, int t, int oldl, int oldt, EventArgs e);

    public event ScrollChangedHandler scrollChanged;
    public EventArgs e = null;

    //Enabling all required constructors
    public NotifyingScrollRecyclerView(Context context) : base(context)
    {

    }

    public NotifyingScrollRecyclerView(Context context, IAttributeSet attrs) : base(context, attrs)
    {

    }

    public NotifyingScrollRecyclerView(IntPtr ptr, JniHandleOwnership ownership) : base(ptr, ownership)
    {

    }

    public NotifyingScrollRecyclerView(Context context, IAttributeSet attrs, int defStyle) : base(context, attrs, defStyle)
    {

    }

    //This method attribute allows us to register the inbuilt OnScrollChanged event that fires when scrolling a ScrollView
    [Android.Runtime.Register("onScrollChanged", "(IIII)V", "GetOnScrollChanged_IIIIHandler")]
    protected override void OnScrollChanged(int l, int t, int oldl, int oldt)
    {
        base.OnScrollChanged(l, t, oldl, oldt);
        scrollChanged(l, t, oldl, oldt, e);
    }



}


//Set an event listener
public class ScrollViewChangedListener
{
    private Activity activity;
    private NotifyingScrollRecyclerView scrollView;
    private Android.Support.V7.App.ActionBar actionBar;
    private Drawable actionBarDrawable;
  be changed
    public ScrollViewChangedListener(Activity a, NotifyingScrollRecyclerView n)
    {
        n.scrollChanged += ScrollChangedTarget;
        this.activity = a;
        this.scrollView = n;
        this.actionBar = ((UserPageActivity)a).SupportActionBar;

        this.actionBarDrawable = a.GetDrawable(Resource.Drawable.actionbar_background);
        this.actionBarDrawable.SetAlpha(0);

    }

    //Handle the changing of the scroll
    public void ScrollChangedTarget(int l, int t, int oldl, int oldt, EventArgs e)
    {
        //You set the View you want to be your header as a header height, and then get it's height
        int headerHeight = activity.FindViewById<ImageView>(Resource.Id.profilebanner).Height -
        this.actionBar.Height;
        float ratio = (float)Math.Min(Math.Max(t, 0), headerHeight) / headerHeight;
        int newAlpha = (int)(ratio * 255);

            this.actionBarDrawable.SetAlpha(newAlpha);
            this.actionBar.SetBackgroundDrawable(this.actionBarDrawable);


    }

}

这是调用片段的 Activity（在这种情况下，除了调用片段外，它没有做任何特别的事情）：

[Activity(Label = "UserPageActivity")]
public class UserPageActivity : BaseActivity
{
    protected override int LayoutResource => Resource.Layout.activity_user_page;
    UserViewModel viewModel;
    TextView username;
    TextView usernameToolbar;
    Button followButton;


    ViewPager pager;
    UserTabsAdapter adapter;
    bool IsLoggedUser;

    protected override void OnCreate(Bundle savedInstanceState)
    {
        IsLoggedUser = Intent.GetStringExtra("userId").Equals(LoginController.GetInstance().CurrentUser.Email);
        base.OnCreate(savedInstanceState);
        viewModel = new UserViewModel();
        viewModel.UserLoaded += new UserViewModel.UserLoadedHandler(OnUserLoaded);
        viewModel.LoadUserCommand.Execute(Intent.GetStringExtra("userId"));
        username = FindViewById<TextView>(Resource.Id.profilename);
        usernameToolbar = FindViewById<TextView>(Resource.Id.usernamePage);
        followButton = FindViewById<Button>(Resource.Id.followButton);

        username.Text = Intent.GetStringExtra("username");
        usernameToolbar.Text = Intent.GetStringExtra("username");

        adapter = new UserTabsAdapter(this, SupportFragmentManager);
        pager = FindViewById<ViewPager>(Resource.Id.user_viewpager);
        var tabs = FindViewById<TabLayout>(Resource.Id.tabs);
        pager.Adapter = adapter;
        tabs.SetupWithViewPager(pager);
        pager.OffscreenPageLimit = 5;


        pager.PageSelected += (sender, args) =>
        {
            var fragment = adapter.InstantiateItem(pager, args.Position) as IFragmentVisible;

            fragment?.BecameVisible();
        };
    }

    private void OnUserLoaded(bool loaded)
    {

    }

    protected override void OnStart()
    {
        base.OnStart();

        if (IsLoggedUser)
        {
            followButton.Visibility = ViewStates.Gone;

        }
        else
        {
            bool following;
            if (LoginController.GetInstance().CurrentUser.FollowsUsers.ContainsKey(Intent.GetStringExtra("userId")))
            {
                followButton.Text = "Unfollow";
                following = true;
            }
            else
            {
                followButton.Text = "Follow";
                following = false;
            }

            followButton.Click += (object sender, EventArgs e) =>
            {
                followButton.Enabled = false;
                if (following)
                {
                    UserService service = ServiceLocator.Instance.Get<UserService>();

                    service.SetUser(LoginController.GetInstance().CurrentUser);
                    service.RemoveFollowsUserCommand.Execute(viewModel.LoadedUser.Email);

                    service.SetUser(viewModel.LoadedUser);
                    service.RemoveFollowedByUserCommand.Execute(LoginController.GetInstance().CurrentUser.Email);

                    followButton.Text = "Follow";
                    following = false;
                }
                else
                {
                    UserService service = ServiceLocator.Instance.Get<UserService>();

                    service.SetUser(LoginController.GetInstance().CurrentUser);
                    service.AddFollowsUserCommand.Execute(viewModel.LoadedUser);

                    service.SetUser(viewModel.LoadedUser);
                    service.AddFollowedByUserCommand.Execute(LoginController.GetInstance().CurrentUser);

                    followButton.Text = "Unfollow";
                    following = true;
                }
                followButton.Enabled = true;
            };
        }
    }
}

class UserTabsAdapter : FragmentStatePagerAdapter
{
    string[] titles;

    public override int Count => titles.Length;

    public UserTabsAdapter(Context context, Android.Support.V4.App.FragmentManager fm) : base(fm)
    {
        titles = context.Resources.GetTextArray(Resource.Array.user_sections);
    }

    public override Java.Lang.ICharSequence GetPageTitleFormatted(int position) =>
                        new Java.Lang.String(titles[position]);

    public override Android.Support.V4.App.Fragment GetItem(int position)
    {
        switch (position)
        {
            case 0: return UserContestsFragment.NewInstance();
            case 1: return UserPartecipationsFragment.NewInstance();
            case 2: return GlobalContestFragment.NewInstance();
            case 3: return MessagesFragment.NewInstance();
        }
        return null;
    }

    public override int GetItemPosition(Java.Lang.Object frag) => PositionNone;
}

这是为 recyclerview 设置侦听器的片段：

      public class UserContestsFragment : AbstractRefresherFadingToolbarFragment<Contest>
{
    public static UserContestsFragment NewInstance() =>
        new UserContestsFragment { Arguments = new Bundle() };


    public override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
    }

    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        ContestViewModel viewModel = new ContestViewModel();
        base.ViewModel = viewModel;
        base.LoadItemsCommand = viewModel.LoadAllByCreatorUserCommand;
        base.param = Activity.Intent.GetStringExtra("userId");
        base.adapter = new ContestsAdapter(Activity, viewModel);
        var view = base.OnCreateView(inflater, container, savedInstanceState);

        ScrollViewChangedListener listener = new ScrollViewChangedListener(Activity, recyclerView);
        return view;
    }

这是负责设置布局的片段所需的抽象片段：

  public abstract class AbstractRefresherFadingToolbarFragment<T> : Android.Support.V4.App.Fragment, IFragmentVisible
{
    public ICollectionViewModel<T> ViewModel;
    public ICommand LoadItemsCommand;
    public object param; //parametro per il LoadItemsCommand
    public ItemsAdapter<T> adapter;
    public SwipeRefreshLayout refresher;
    public ProgressBar progress;
    public NotifyingScrollRecyclerView recyclerView;
    //LruCache cache = new LruCache((int)(Runtime.GetRuntime().MaxMemory() / 4));

    public override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
    }

    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        View view = inflater.Inflate(Resource.Layout.fragment_fading_toolbar, container, false);
        recyclerView = view.FindViewById<NotifyingScrollRecyclerView>(Resource.Id.recyclerView);
        //ScrollViewChangedListener listener = new ScrollViewChangedListener((UserPageActivity)Activity, recyclerView);
        //adapter.cache = cache;
        recyclerView.HasFixedSize = true;
        recyclerView.SetAdapter(adapter);
        recyclerView.SetItemViewCacheSize(4);
        //recyclerView.ChildViewAttachedToWindow += new EventHandler<RecyclerView.ChildViewAttachedToWindowEventArgs>(OnChildViewAttached);
        //recyclerView.ChildViewDetachedFromWindow += new EventHandler<RecyclerView.ChildViewDetachedFromWindowEventArgs>(OnChildViewDetached);

        refresher = view.FindViewById<SwipeRefreshLayout>(Resource.Id.refresher);
        refresher.SetColorSchemeColors(Resource.Color.accent);

        progress = view.FindViewById<ProgressBar>(Resource.Id.progressbar_loading);
        progress.Visibility = ViewStates.Gone;

        return view;
    }


}

Answer 1

我没有阅读您的全部代码，但我查看了您在问题中链接的网站。您要使用的隐藏操作栏的功能由支持库中的 CollapsingToolbarLayout 处理。要了解如何使用它，请转到 Cheesesquare。它是支持库小部件的完整示例，无需任何更改即可构建和运行。

编辑： RecyclerView 有一个名为 AddOnScrollListener 的方法。使用它代替 OnScrollChanged。如果您使用从 RecyclerView 继承的 class，则可以在该 class.

的所有构造函数中调用它

OnScrollChanged 没有获取 RecyclerView 参数

OnScrollChanged doesn't get the RecyclerView parameters

c#

android

android-recyclerview

onscrollchanged