在 Xamarin Forms 中选择项目时集合视图刷新问题

Question

我在 Xamarin 表单中使用 集合视图 实现了水平列表。下划线不正确，选择项目时会迟到。刷新为时已晚。正如您在下面的视频中看到的那样

我的Xaml代码

  <CollectionView
                x:Name="rooms_List"
                IsEnabled="True"
                SelectedItem="{Binding SelectedRoom}"
                SelectionChangedCommand="{Binding Source={x:Reference ThePage}, Path= BindingContext.RoomChanged}"
                ItemsLayout = "HorizontalList"
                SelectionChanged="RoomCollectionSelectionChanged"
                BackgroundColor = "white"
                HeightRequest="50"
                SelectionMode="Single"
                HorizontalScrollBarVisibility="Never"
                ItemsSource="{Binding RoomList}">
                <CollectionView.ItemTemplate >
                    <DataTemplate>
                            <Grid>
                                <StackLayout VerticalOptions="Start" Orientation="Vertical">
                                    <Label  Text ="{Binding RoomName}"  Padding="20,10,20,0" />
                                    <BoxView x:Name="line" HeightRequest="3" IsVisible="{Binding IsSelected}" BackgroundColor="#1484B8" WidthRequest="5" Margin="18,0,15,0" />
                                </StackLayout>
                            </Grid>
                    </DataTemplate>
                </CollectionView.ItemTemplate>
            </CollectionView>

我的 Xaml.cs RoomCollectionSelectionChanged

 private void RoomCollectionSelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (e.CurrentSelection.Count == 0)
            {
                room_image.IsVisible = true;
            }
            else
            {
                var selectedItem = e.CurrentSelection.FirstOrDefault() as Room;
                selectedRoom = selectedItem.RoomName;
                if (selectedRoom == "All")
                {
                    room_image.IsVisible = false;
                }
                else if (e.PreviousSelection.Count == 1)
                {
                    var previousItem = (e.PreviousSelection.FirstOrDefault() as Room)?.RoomName;
                    if (previousItem != "")
                    {
                        room_image.IsVisible = true;
                        room_image.Source = selectedItem.RoomImage;
                    }
                }
                else
                {
                    room_image.IsVisible = true;
                    room_image.Source = selectedItem.RoomImage;
                }
            }
        }

我的视图模型

private ObservableCollection<Room> roomList { get; set; }

        public ObservableCollection<Room> RoomList
        {
            get { return roomList; }
            set
            {
                roomList = value;
                OnPropertyChanged(nameof(RoomList));
            }
        }

        private Room selectedRoom { get; set; }

        public Room SelectedRoom
        {
            get { return selectedRoom; }
            set
            {
                selectedRoom = value;
            }
        }

        public bool isSelected { get; set; }

        public bool IsSelected
        {
            get { return isSelected; }
            set
            {
                if (value != isSelected)
                {
                    isSelected = value;
                    OnPropertyChanged(nameof(IsSelected));
                }
            }
        }

        private Room previousSelectedRoom;

        private void SelectedRoomEvent()
        {
            if (SelectedRoom != null)
            {
                DevicePage.checkRoom = true;
                string RoomName = SelectedRoom.RoomName;

                if (RoomName.Equals("All"))
                {
                    GetDeviceAndRoomData();
                }
                else
                {
                    int RoomId = SelectedRoom.RoomId;

                    if (previousSelectedRoom != null)
                    {
                        previousSelectedRoom.IsSelected = false;
                    }
                    previousSelectedRoom = SelectedRoom;
                    previousSelectedRoom.IsSelected = true;

                }
        }

我的模型

public class Room
    {
        [PrimaryKey, AutoIncrement]
        public int Id { get; set; }
        [JsonProperty("roomId")]
        public int RoomId { get; set; }
        [JsonProperty("serialNumber")]
        public string SerialNumber { get; set; }
        [JsonProperty("roomName")]
        public string RoomName { get; set; }
        [JsonProperty("roomImage")]
        public string RoomImage { get; set; }
        [JsonIgnore]
        public bool IsSelected { get; set; }
    }

请提供解决此问题的建议enter image description here

Answer 1

我看到您在代码中使用了 e. PreviousSelection 。这比我在我的存储库中所做的要好，所以我修改了 github ToolmakerSteve - repo XFIOSHorizCollViewScrollBug 以使用它。

我在这个文件的几个地方做了修改：

using System.Collections.ObjectModel;
using System.Linq;
using Xamarin.Forms;

namespace XFIOSHorizCollViewScrollBug
{
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
            InitRoomList();
            BindingContext = this;

            // After set BindingContext, so RoomCollectionSelectionChanged gets called.
            var room = RoomList[0];
            rooms_List.SelectedItem = room;
        }

        public ObservableCollection<Room> RoomList { get; set; }

        private void RoomCollectionSelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            var previousItem = e.PreviousSelection.FirstOrDefault() as Room;
            DeselectRoom(previousItem);
            var selectedItem = e.CurrentSelection.FirstOrDefault() as Room;
            SelectRoom(selectedItem);
        }

        private void DeselectRoom(Room room)
        {
            if (room != null)
            {
                room.IsSelected = false;
            }
        }

        private void SelectRoom(Room room)
        {
            if (room != null) {
                room.IsSelected = true;
                rooms_List.ScrollTo(room, position: ScrollToPosition.Center, animate: false);
            }
        }

        string[] roomNames = new string[] {
            "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight"
        };

        private void InitRoomList()
        {
            var rooms = new ObservableCollection<Room>();
            foreach (var name in roomNames) {
                rooms.Add(new Room(name));
            }

            RoomList = rooms;
        }
    }
}

其他文件同。

请下载我的存储库，构建并运行它，验证它是否有效。下划线的更改会立即发生 - 只要您单击一个项目。

然后将其与您的代码进行比较。更改您的代码，直到它与工作仓库的功能相匹配。

在 Xamarin Forms 中选择项目时集合视图刷新问题

Collection View Refreshing issue While Selecting Item in Xamarin Forms

c#

android

collectionview

ios

xamarin