问题描述
很多小时我都在尝试将 ItemSelected 值传递给我的 MainPage ToolbarItem x:name="CityClick".这是我在 Cities 类后面的 Cities 类和 City 类的代码:
Many hours I am trying to pass ItemSelected value to my MainPage ToolbarItem x:name="CityClick". This is my code of Cities class and City class behind of Cities class:
public partial class Cities : ContentPage
{
private Action<object, SelectedItemChangedEventArgs> onItemSelected;
public Cities()
{
InitializeComponent();
Label header = new Label
{
Text = "Select here",
FontSize = Device.GetNamedSize(NamedSize.Large, typeof(Label)),
HorizontalOptions = LayoutOptions.Center
};
List<City> cities = new List<City>
{
new City("C1"),
new City("City2")
};
ListView listView = new ListView
{
ItemsSource = cities,
ItemTemplate = new DataTemplate(() =>
{
Label nameLabel = new Label();
nameLabel.SetBinding(Label.TextProperty, "Name");
BoxView boxView = new BoxView();
return new ViewCell
{
View = new StackLayout
{
Padding = new Thickness(0, 5),
Orientation = StackOrientation.Horizontal,
Children =
{
...
}
}
};
})
};
this.Padding = new Thickness(10, Device.OnPlatform(20, 0, 0), 10, 5);
this.Content = new StackLayout
{
Children =
{
..
}
};
listView.ItemSelected += async (sender, e) =>
{
if (e.SelectedItem == null)
{
return;
}
else
{
await Navigation.PopAsync();
}
};
}
public Cities(Action<object, SelectedItemChangedEventArgs> onItemSelected)
{
this.onItemSelected = onItemSelected;
}
}
public class City
{
public City()
{
this.Name = Name;
}
public City(string name)
{
this.Name = name;
}
public string Name { set; get; }
};
这是我初始化 City() 类的 MainPage 类，但是当我调试时它显示 obj.Name 为 null :
This is my MainPage class where I initialize City() class, but when I am debugging it shows null for obj.Name :
public partial class MainPage : MasterDetailPage
{
public MainPage()
{
InitializeComponent();
masterPage.ListView.ItemSelected += OnItemSelected;
CityClick.Clicked += async (sender, e) =>
{
await Detail.Navigation.PushAsync(new Cities());
};
City obj = new City();
Cities obj2 = new Cities();
var myobject = Application.Current.Properties[CityClick.Text];
myobject = obj.Name;
if (obj.Name == null)
{
if (Application.Current.Properties.ContainsKey(CityClick.Text))
{
var id = Application.Current.Properties[CityClick.Text] as string;
CityClick.Text = obj.Name;
}
}
}}
这是 MainPage xaml:
And this is MainPage xaml:
<?xml version="1.0" encoding="UTF-8"?>
<MasterDetailPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:LearningProject;assembly=LearningProject"
x:Class="LearningProject.MainPage"
MasterBehavior="Popover">
<ContentPage.ToolbarItems>
<ToolbarItem x:Name="CityClick"
Text="City:"
Order="Primary">
</ToolbarItem>
</ContentPage.ToolbarItems>
<MasterDetailPage.Master>
<local:MasterPage x:Name="masterPage" />
</MasterDetailPage.Master>
<MasterDetailPage.Detail>
<NavigationPage>
<x:Arguments>
<local:UnpaidVehicle />
</x:Arguments>
</NavigationPage>
</MasterDetailPage.Detail>
</MasterDetailPage>
所以当我调试时，它显示 ItemSelected 包含一些字符串名称.但是当我调试 MainPage.xaml.cs 时，它显示它为空.为什么 obj.Name 没有达到 Cities 类的值?
So when I am debuging, it is shows that ItemSelected hold some string name. But when I am debuging MainPage.xaml.cs it shows that it is null. Why obj.Name do not reach value from Cities class?
推荐答案
Ok ，所以我以这样的方式解决了值传递问题:我改变了 private ActiononItemSelected; 到 公共事件 EventHandlerOnSelectedCity; 此事件处理程序将在 MainPage 类中使用.它会检测何时选择了项目.然后在 listView.ItemSelected else 部分中，我添加了对所选对象的解析: OnSelectedCity((City)e.SelectedItem, null); 完整的 else 部分如下所示:
Ok , so I solved value passing issue in such a way: I changed private Action<object, SelectedItemChangedEventArgs> onItemSelected; to public event EventHandler<SelectedItemChangedEventArgs> OnSelectedCity; This event handler will be used in MainPage class. And It will detects when item is selected. Then in listView.ItemSelected else section I added parsing of my selected object : OnSelectedCity((City)e.SelectedItem, null); Full else section looks like this:
else
{
((ListView)sender).SelectedItem = null;
if (OnSelectedCity != null)
{
OnSelectedCity((City)e.SelectedItem, null);
}
await Navigation.PopAsync();
}
然后在 CityClick.Clicked 事件的 MainPage 类中，我像这样初始化 Cities 类:
Then in MainPage class of CityClick.Clicked event I initialize Cities class like this:
CityClick.Clicked += async (sender, e) =>
{
Cities page = new Cities();
page.OnSelectedCity += Page_OnSelectedCity;
await Detail.Navigation.PushAsync(page);
};
这里我从 Cities 类调用事件.我自动创建 Page_OnSelectedCity 方法.在那里我传递类的对象值并将其分配给我的 ToolBarItem 的 CityClick.Text 标签，在那里我看到了来自 City 类的值！
Here I call event from Cities class. And I create automaticly Page_OnSelectedCity method. There I pass object value of class and assign it to my CityClick.Text label of ToolBarItem, there I see value from my City class!
void Page_OnSelectedCity(object sender, SelectedItemChangedEventArgs e)
{
var city = (City)(sender);
CityClick.Text = city.Name;
}
这篇关于Xamarin 传递列表项值，从一个类到 MainPage 类 ToolbarItem的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！