Question

我想单击列表视图的视单元中的包和图像来更改标签文本和图像。我正在将命令用于click事件，并在扩展InotifyPropertyChange的ViewModelClass中实现了该命令。单击图像或标签后，我的视图没有更新。请帮助。

公共类BookPageViewModel：INotifyPropertyChanged， { #region字段私有ObservableCollection feeds = new ObservableCollection（）;

    public ObservableCollection<FeedsModel> Feeds {
        get
        {
            return feeds; 
        }
        set {
          if(value != feeds)
            {
                feeds = value;
                OnPropertyChanged("Feeds");
           }
        }
    }

    private ICommand onLikePostClicked;
    public ICommand OnLikePostClicked
    {
        get { return onLikePostClicked; }
    }

    public DayBookPageViewModel(Page page, SfListView sfListView)
    {

        GetAllFeeds(Settings.UserIdSettings);
        this.page = page;
        this.sfListView = sfListView;
        #region Commands execution 

        onLikePostClicked = new Command((e) =>
        {
            var item = (e as FeedsModel);

            if (!string.IsNullOrEmpty(item.Love))
            {
                bool like_status = false;
                string[] strarray = item.Love.Split(',');
                for (int i = 0; i < strarray.Length; i++)
                {
                    if (strarray[i] == Settings.UserIdSettings)
                    {
                        like_status = true;

                        break;
                    }
                    else
                    {
                        like_status = false;
                    }

                }

                if(like_status)
                {
                    // unlike 
                if (!NetworkConnectionClass.GetInstance().IsConnectedToInternet())
                    ShowAlerts.GetInstance().ACRLibAlert(Strings.InternetAlert, Strings.Ok);
                else
                {

                        if (item != null)
                        {
                            Device.BeginInvokeOnMainThread(delegate
                            {


                                item.LikeImageSource = ImageSource.FromFile("like_hover");
                                item.LikeLabelColor = (Color)Application.Current.Resources["defaultLabels_color"];
                                OnPropertyChanged("Feeds");
                            });
                            DislikeApi dislikePostApi = new DislikeApi(this, this);
                            dislikePostApi.DisLikePost(Settings.UserIdSettings, item.postId.ToString());
                        }
                }    
                }
                else
                {
                    // like 
                if (!NetworkConnectionClass.GetInstance().IsConnectedToInternet())
                    ShowAlerts.GetInstance().ACRLibAlert(Strings.InternetAlert, Strings.Ok);
                else
                {
                        if (item != null)
                        {

                            //Todo;
                            //********* UI not updating : need to fixed ***********
                            Device.BeginInvokeOnMainThread(delegate
                            {

                                item.LikeImageSource = ImageSource.FromFile("like");
                                item.LikeLabelColor = (Color)Application.Current.Resources["appThemeColor"];
                                OnPropertyChanged("Feeds");


                            });
                            LikePostApi likePostApi = new LikePostApi(this, this);
                            likePostApi.LikePost(Settings.UserIdSettings, item.postId.ToString());
                        }
                }   
                }

            }
            else

            {
                if (!NetworkConnectionClass.GetInstance().IsConnectedToInternet())
                    ShowAlerts.GetInstance().ACRLibAlert(Strings.InternetAlert, Strings.Ok);
                else
                {
                    if (item != null)
                    {

                        //Todo;
                        //********* UI not updating : need to fixed ***********


                        Device.BeginInvokeOnMainThread( delegate
                        {    if (!item.Love.Contains(Settings.UserIdSettings))
                            {

                            likeimageSource = ImageSource.FromFile("like");
                            item.LikeImageSource = ImageSource.FromFile("like");
                            item.LikeLabelColor = (Color)Application.Current.Resources["appThemeColor"];
                            OnPropertyChanged("Feeds");


                        });


      #endregion
    }

}

//  This is inside the viewcell of a listview        
        <Label x:Name="likeLabel" TextColor="{Binding LikeLabelColor, Mode=TwoWay}" Text="Like " LineBreakMode="CharacterWrap"  FontSize="12" Grid.Row="0" Grid.Column="1">
        <Label.Margin>
             <OnPlatform x:TypeArguments="Thickness">
  <On Platform="iOS" Value="0,15.5,0,0" />
  <On Platform="Android" Value="0,14,0,0" />
</OnPlatform>   
            </Label.Margin>


            <Label.GestureRecognizers>
                <TapGestureRecognizer   Command="{Binding Path=BindingContext.OnLikePostClicked, Source={x:Reference customListView}}" CommandParameter ="{Binding .}"  NumberOfTapsRequired="1" />
            </Label.GestureRecognizers>
        </Label>

Answer 1

您需要在INotifyPropertyChanged对象上实现FeedModel。这就是发生更改的地方，因此您希望在其中发生任何事情时通知UI。

如果您想节省很多样板代码，请查看PropertyChanged.Fody，它会在编译时为您生成INotifyPropertyChanged代码。

Xamarin Froms：单击Listview的视单元内的Label时，UI上的Label文本和图像未更新

1 个答案: