UWP Custom ListView向下滚动

Question

所以,我有一个listview,每当创建一个项目滚动到该项目(底部)时我都想要它.因为我正在使用MVVM,所以我找到了关于如何创建一个从listview继承的新控件的非常好的解释.问题是这个答案(第三个)是指6年前的WPF.我正在制作一个UWP应用程序,因此我复制了代码并尝试将其格式化为我的需求.下面的代码不会给出任何错误或异常,而是加载"ChatListView",因为我称之为完美,然后什么都不做.与原始代码相比,注释仅进行了一些编辑.

我能做什么 ？先感谢您!

public class ChatListView : ListView
{
    //Define the AutoScroll property. If enabled, causes the ListBox to scroll to 
    //the last item whenever a new item is added.
    public static readonly DependencyProperty AutoScrollProperty =
        DependencyProperty.Register(
            "AutoScroll",
            typeof(Boolean),
            typeof(ChatListView),
            new PropertyMetadata(
                true, //Default value.
                new PropertyChangedCallback(AutoScroll_PropertyChanged)));

    //Gets or sets whether or not the list should scroll to the last item 
    //when a new item is added.
    public bool AutoScroll
    {
        get { return (bool)GetValue(AutoScrollProperty); }
        set { SetValue(AutoScrollProperty, value); }
    }

    //Event handler for when the AutoScroll property is changed.
    //This delegates the call to SubscribeToAutoScroll_ItemsCollectionChanged().
    //d = The DependencyObject whose property was changed.</param>
    //e = Change event args.</param>
    private static void AutoScroll_PropertyChanged(
        DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        SubscribeToAutoScroll_ItemsCollectionChanged(
            (ChatListView)d,
            (bool)e.NewValue);
    }

    //Subscribes to the list items' collection changed event if AutoScroll is enabled.
    //Otherwise, it unsubscribes from that event.
    //For this to work, the underlying list must implement INotifyCollectionChanged.
    //
    //(This function was only creative for brevity)

    //listBox = The list box containing the items collection.
    //subscribe = Subscribe to the collection changed event?
    private static void SubscribeToAutoScroll_ItemsCollectionChanged(
        ChatListView listView, bool subscribe)
    {
        INotifyCollectionChanged notifyCollection =
            listView as INotifyCollectionChanged;
        if (notifyCollection != null)
        {
            if (subscribe)
            {
                //AutoScroll is turned on, subscribe to collection changed events.
                notifyCollection.CollectionChanged +=
                    listView.AutoScroll_ItemsCollectionChanged;
            }
            else
            {
                //AutoScroll is turned off, unsubscribe from collection changed events.
                notifyCollection.CollectionChanged -=
                    listView.AutoScroll_ItemsCollectionChanged;
            }
        }
    }

    //Event handler called only when the ItemCollection changes
    //and if AutoScroll is enabled.

    //sender = The ItemCollection.
    //e = Change event args.
    private void AutoScroll_ItemsCollectionChanged(
        object sender, NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == NotifyCollectionChangedAction.Add)
        {
            int count = Items.Count;
            ScrollIntoView(Items[count - 1]);
        }
    }

    //Constructor a new ChatListView.
    public ChatListView()
    {
        //Subscribe to the AutoScroll property's items collection 
        //changed handler by default if AutoScroll is enabled by default.
        SubscribeToAutoScroll_ItemsCollectionChanged(
            this, (bool)AutoScrollProperty.GetMetadata(typeof(ChatListView)).DefaultValue);
    }
}

Answer 1

如果你想创建您可以使用聊天应用程序ItemsStackPanel的ItemsUpdatingScrollMode特定属性KeepLastItemInView值滚动到最新项.

用法:

<ListView>
    <ListView.ItemsPanel>
        <ItemsPanelTemplate>
            <ItemsStackPanel ItemsUpdatingScrollMode="KeepLastItemInView" />
        </ItemsPanelTemplate>
    </ListView.ItemsPanel>
</ListView>

注意:KeepLastItemInView枚举成员是在14393 SDK中引入的.

相关链接:https: //docs.microsoft.com/en-us/uwp/api/Windows.UI.Xaml.Controls.ItemsStackPanel#properties_