发布：2021/10/22 23:50:24作者：管理员 来源：本站 浏览次数：1104
使用MVVM模式,我有一个Model,viewmodel和View,它包含一个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工作,并且可以在对视图执行操作时更新适当行的Model类的属性,但是我无法刷新视图,从ObservableCollection中的Model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,如何刷新ListView？
这是我想要做的一个简单示例：每行包含一个Button和Label.单击按钮后,我可以更新标签,该标签将反映在屏幕上.我需要做的是更新模型,反过来应该强制更新视图.但是,我不能让这个工作.在实际应用程序中,Model的更新将在业务逻辑层中,而不是在视图中,之后我需要强制刷新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;
}
}
}
解决方法
我认为你的模型需要实现INotifyPropertyChanged.因此,UI知道模型中的值已更改
这样的事情：
public class Model : INotifyPropertyChanged
{
// boiler-plate
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this,new PropertyChangedEventArgs(propertyName));
}
protected bool SetField<T>(ref T field,T value,string propertyName)
{
if (EqualityComparer<T>.Default.Equals(field,value)) return false;
field = value;
OnPropertyChanged(propertyName);
return true;
}
// props
private string _count;
public string Count
{
get { return _count; }
set { SetField(ref _count,value,"Count"); }
}
}
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