我正在使用 Xamarin.Forms 并尝试使用 MVVM 架构。
我有一个内容页面,上面有一个简单的 ListView 。 ListView 的项目源属性绑定(bind)到我的 ViewModel。我可以很好地填充列表。所有项目都按其应有的方式显示。
当我单击列表中的某个项目时,我需要根据所选项目导航到不同的页面。这是行不通的。只有当我直接引用我的底层模型时它才会起作用(这不是我想要做的)
我已经编码了 ListView.ItemSelected 事件。但是,“Item Selected”事件无法确定所选列表项的“display_text”是什么。如何实现此目的,而无需直接从 View (页面)引用模型?
主页代码:
public partial class MainPage : ContentPage
{
private int intPreJobFormID = 0;
public MainPage()
{
InitializeComponent();
BindingContext = new MainPageViewModel();
Label lblHeader = new Label
{
Text = "HW Job Assessments",
FontSize = ViewGlobals.lblHeader_FontSize,
HorizontalOptions = ViewGlobals.lblHeader_HorizontalOptions,
FontAttributes = ViewGlobals.lblHeader_FontAttributes,
TextColor = ViewGlobals.lblHeader_TextColor
};
//Create the Main Menu Items List View
var lvMain = new ListView
{
//Pull down to refresh list
IsPullToRefreshEnabled = true,
//Define template for displaying each item.
//Argument of DataTemplate constructor is called for each item. It must return a Cell derivative.
ItemTemplate = new DataTemplate(() =>
{
//Create views with bindings for displaying each property.
Label lblDisplayText = new Label();
lblDisplayText.SetBinding(Label.TextProperty, "display_text");
lblDisplayText.FontSize = Device.GetNamedSize(NamedSize.Medium, typeof(Label));
//Return an assembled ViewCell.
return new ViewCell
{
View = new StackLayout
{
Padding = new Thickness(20, 5, 0, 0),
Orientation = StackOrientation.Horizontal,
Children =
{
new StackLayout
{
VerticalOptions = LayoutOptions.Center,
Spacing = 0,
Children =
{
lblDisplayText
}
}
}
}
};
})
};
lvMain.SetBinding(ListView.ItemsSourceProperty, "MainMenuItems");
lvMain.ItemSelected += lvMain_ItemSelected;
}
private async void lvMain_ItemSelected(object sender, SelectedItemChangedEventArgs e)
{
var lv = (ListView)sender;
if (e.SelectedItem == null)
{
return; //ItemSelected is called on deselection which results in SelectedItem being set to null
}
//var item = e.SelectedItem as TableMainMenuItems; //This is what I DON'T want to use because it references my Model directly.
var item = e.SelectedItem;
switch (item.display_text) //This is what I need. I can't get this unless I reference my Model "TableMainMenuItems" directly.
{
case "Forms List":
await Navigation.PushAsync(new FormsListPage());
break;
case "New Pre-Job":
await Navigation.PushAsync(new PreJobPage(intPreJobFormID));
break;
}
//Comment out if you want to keep selections
lv.SelectedItem = null;
}
}
MainPageViewModel 代码:
public class MainPageViewModel
{
public int intPreJobFormID = 0;
private DatabaseApp app_database = ViewModelGlobals.AppDB;
private DatabaseFormData formdata_database = ViewModelGlobals.FormDataDB;
private IEnumerable<TableMainMenuItems> lstMaineMenuItems;
private IEnumerable<TableFormData> lstRecentJobs;
public string DisplayText { get; set; }
public IEnumerable<TableMainMenuItems> MainMenuItems
{
get { return lstMaineMenuItems; }
set
{
lstMaineMenuItems = value;
}
}
public IEnumerable<TableFormData> RecentJobs
{
get { return lstRecentJobs; }
set
{
lstRecentJobs = value;
}
}
public MainPageViewModel()
{
intPreJobFormID = app_database.GetForm(0, "Pre-Job Assessment").Id;
MainMenuItems = app_database.GetMainMenuItems();
RecentJobs = formdata_database.GetFormAnswersForForm(intPreJobFormID).OrderByDescending(o => o.date_modified);
}
}
最佳答案
有两种方法可以检索所选项目的绑定(bind)属性。
我个人更喜欢在 View 中处理逻辑,因为它使代码更简单。
1。处理 View 中的逻辑
Actor item
作为您的模型类型:
var item = e.SelectedItem as TableMainMenuItems;
async void lvMain_ItemSelected(object sender, SelectedItemChangedEventArgs e)
{
var listView = (ListView)sender;
listView.SelectedItem = null;
if (e?.SelectedItem is TableMainMenuItems item)
{
switch (item.display_text)
{
case "Forms List":
await Navigation.PushAsync(new FormsListPage());
break;
case "New Pre-Job":
await Navigation.PushAsync(new PreJobPage(intPreJobFormID));
break;
}
}
}
2。处理 View 模型中的逻辑
查看
使用 Command<T>
在 View 和 View 模型之间松散地耦合 ItemSelected 逻辑。创建 event
在 View 模型中,当 View 模型完成逻辑时将触发。
public partial class MainPage : ContentPage
{
public MainPage()
{
var viewModel = new MainPageViewModel();
BindingContext = viewModel;
...
viewModel.NavigationRequested += (s,e) => Device.BeginInvokeOnMainThread(async () => await Navigation.PushAsync(e));
}
...
void lvMain_ItemSelected(object sender, SelectedItemChangedEventArgs e)
{
var listView = (ListView)sender;
listView.SelectedItem = null;
var viewModel = (MainPageViewModel)BindingContext;
viewModel.ListViewItemSelectedCommand?.Invoke(e);
}
}
View 模型
public class MainPageViewModel
{
//...
Command<SelectedItemChangedEventArgs> _listViewItemSelectedCommand;
//...
public event EventHandler<Page> NavigationRequested;
//...
public Command<SelectedItemChangedEventArgs> ListViewItemSelectedCommand => _listViewItemSelectedCommand ??
(_listViewItemSelectedCommand = new Command<SelectedItemChangedEventArgs>(ExecuteListViewItemSelectedCommand));
//...
void ExecuteListViewItemSelectedCommand(SelectedItemChangedEventArgs e)
{
var item = e as TableMainMenuItems;
switch (item?.display_text)
{
case "Forms List":
OnNavigationRequested(new FormsListPage());
break;
case "New Pre-Job":
OnNavigationRequested(new PreJobPage(0));
break;
}
}
void OnNavigationRequested(Page pageToNavigate) => NavigationRequested?.Invoke(this, pageToNavigate);
//...
}
关于c# - 如何使用 MVVM 和 Xamarin.Forms ListView ItemSelected 事件来检索所选项目的绑定(bind)属性?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41387508/