Xamarin Android onScrollListener被多次调用。

Question

我想在我的应用程序中创建一个无限滚动的RecyclerView。它使用一个web服务，并在屏幕上带来一些CardView项目。下面是我到目前为止得到的简化代码，没有包含RecyclerView创建等。

Main.cs

protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        var categoryLayoutManager = new LinearLayoutManager(this);
        categoryList.SetLayoutManager(categoryLayoutManager);
        var onScrollListener = new OnScrollListener(categoryLayoutManager);

        onScrollListener.LoadMoreEvent += (object sender, EventArgs e) =>
        {
            Console.WriteLine("Last");
        };
    }

OnScrollListener.cs

public class OnScrollListener : RecyclerView.OnScrollListener
{
    public delegate void LoadMoreEventHandler(object sender, EventArgs e);
    public event LoadMoreEventHandler LoadMoreEvent;

    private LinearLayoutManager LayoutManager;

    public OnScrollListener(LinearLayoutManager layoutManager)
    {
        LayoutManager = layoutManager;
    }

    public override void OnScrolled(RecyclerView recyclerView, int dx, int dy)
    {
        base.OnScrolled(recyclerView, dx, dy);

        var visibleItemCount = recyclerView.ChildCount;
        var totalItemCount = recyclerView.GetAdapter().ItemCount;
        var pastVisiblesItems = LayoutManager.FindFirstVisibleItemPosition();

        if ((visibleItemCount + pastVisiblesItems) >= totalItemCount)
        {
            LoadMoreEvent(this, null);
        }
    }
}

目前，当滚动到最后一个项目时，我的滚动器被多次调用，所以它带来的项目比需要的多。我希望我的侦听器只被调用一次，获取项目，然后在新的最后一项可见时再次被调用。这与我现在的代码相符吗？谢谢。

Answer 1

简单的答案是向侦听器添加一个IsLoading属性，然后只有当它还没有加载时才加载。这里有一个想法，在你的情况下它可能是什么样子

public class OnScrollListener : RecyclerView.OnScrollListener
{
    public delegate void LoadMoreEventHandler(object sender, EventArgs e);
    public event LoadMoreEventHandler LoadMoreEvent;
    public bool IsLoading { get; set; }
    private LinearLayoutManager LayoutManager;

    public OnScrollListener(LinearLayoutManager layoutManager)
    {
        LayoutManager = layoutManager;
    }

    public override void OnScrolled(RecyclerView recyclerView, int dx, int dy)
    {
        base.OnScrolled(recyclerView, dx, dy);

        var visibleItemCount = recyclerView.ChildCount;
        var totalItemCount = recyclerView.GetAdapter().ItemCount;
        var pastVisiblesItems = LayoutManager.FindFirstVisibleItemPosition();

        if ((visibleItemCount + pastVisiblesItems) >= totalItemCount && !IsLoading)
        {
            IsLoading = true;
            LoadMoreEvent(this, null);

            // after it's done, set it back to false
            IsLoading = false;
        }
    }
}