使用 MVVM 模式,我有一个 Model、ViewModel 和 View,其中包含一个 ListView。ListView 绑定到 ViewModel 的成员,该成员是 Model 类的 ObservableCollection。我可以使初始显示的绑定起作用,并且可以在对视图执行操作时更新模型类上的属性以获取适当的行,但是我无法刷新视图,从 ObservableCollection 中的模型类中提取数据。ListView 类不包含使无效或强制刷新的方法,这将解决我的问题。更新模型上的数据后如何让 ListView 刷新?
这是我正在尝试做的一个简单示例:每行包含一个按钮和标签。单击按钮后,我可以更新标签,这将反映在屏幕上。我需要做的是更新模型,这反过来又会强制更新视图。但是,我无法让它发挥作用。在实际应用中,Model的更新是在业务逻辑层,而不是在视图中,之后需要强制刷新ListView。
示例代码:
using System;
using System.Collections.ObjectModel;
using Xamarin.Forms;
namespace ListViewTest
{
public class Model
{
public static int ids = 0;
public Model(string count)
{
Id = +1;
Count = count;
}
public int Id { get; set; }
public string Count { get; set; }
}
public class ModelList : ObservableCollection<Model>
{
}
public class ViewModel
{
ModelList list = new ModelList();
public ModelList ViewModelList
{
get { return list; }
set
{
list = value;
}
}
}
public partial class MainPage : ContentPage
{
public ViewModel viewModel;
public class DataCell : ViewCell
{
public DataCell()
{
var Btn = new Button();
Btn.Text = "Click";
var Data = new Label();
Data.SetBinding(Label.TextProperty,"Count");
Btn.Clicked += (object sender, EventArgs e) =>
{
Model model = (Model)(((Button)sender).Parent.BindingContext);
int count = Convert.ToInt32(model.Count);
count++;
model.Count = count.ToString();
// Need to refresh ListView from data source here... How???
};
StackLayout s = new StackLayout();
s.Orientation = StackOrientation.Horizontal;
s.Children.Add(Btn);
s.Children.Add(Data);
this.View = s;
}
}
public MainPage ()
{
viewModel = new ViewModel();
viewModel.ViewModelList.Add(new Model("0"));
viewModel.ViewModelList.Add(new Model("0"));
InitializeComponent();
}
public void InitializeComponent()
{
ListView listView = new ListView
{
ItemsSource = viewModel.ViewModelList,
ItemTemplate = new DataTemplate(() =>
{
return new DataCell();
})
};
Content = listView;
}
}
}