Question

我创建了一个Xamarin foms应用程序，随着时间的推移我会收到消息，我总是希望新消息显示在我的ListView按钮上，因为它们正在进入。

目前我的网页看起来像这样：

 <StackLayout>
   <Button  Text="Login"  />
   <ListView  x:Name="MessageBox" ItemsSource="{Binding TempTest}" ></ListView>
   <Button Command="{Binding AddMessage}" Text="Login"/>
 </StackLayout>

我无法弄清楚如何从我的ViewModel类滚动，有关如何实现这一点的任何想法？

到目前为止，我能找到的最好的是：http://www.infinite-x.net/2014/10/30/using-the-xamarin-forms-1-3-0-listview-scrollto-method/

但他现在甚至没有考虑过使用MVVM。

Answer 1

那么，不是优雅的方式，我知道解决这个问题就是从你的ViewModel中暴露Action<Message>，然后你的ContentPage会初始化Action并告诉它滚动。类似于以下内容（只需将Message替换为真正的模型名称）。

ContentPage：

public partial class MessagePage : ContentPage {

    private MessageViewModel _viewModel;

    public MessagePage() {
        _viewModel = new MessageViewModel();

        BindingContext = _viewModel;

        _viewModel.OnMessageAdded = message => { //We tell the action to scroll to the passed in object here
            MessageBox.ScrollTo(message, ScrollToPosition.MakeVisible, true);
        }
    }
}

视图模型：

public class MessageViewModel {
    public Action<Message> OnMessageAdded { get; set; }

    public ICommand AddMessage { get; protected set; }

    private ObservableCollection<Message> _tempTest;
    public  ObservableCollection<Message> TempTest {
        get { return _tempTest ?? (_tempTest = new ObservableCollection<Message>()); }
        set {
            if(_tempTest != value) {
                _tempTest = value;
                OnPropertyChanged();
            }
        }
    }

    public MessageViewModel() {
        AddMessage = new Command(async () => {
            Message message = SomeClass.GetMessage(); //Get your object from your separate class

            TempTest.Add(message); //Add it to the list that your ListView binds to

            OnMessageAdded?.Invoke(message); //Now run the Action which, if it is not null, your ContentPage should have set to do the scrolling

            //Or if you are not using C#6:
            //Action<Message> onMessageAdded = OnMessageAdded;

            //if(onMessageAdded != null) { onMessageAdded.Invoke(message); }
        });
    }
}

Xamarin形成滚动到buttom

1 个答案: