C# MVVM导航强制关闭Xamarin表单
我尝试在我的xamarin表单中使用mvvm，但我仍然对每个页面中的导航有点困惑，我已经创建了界面和导航服务来处理xamarin表单中的所有导航，没有错误代码行，但是当我单击buton并尝试导航到其他页面时，它总是崩溃。这是我的一些代码 我的界面C# MVVM导航强制关闭Xamarin表单,c#,mvvm,xamarin.forms,C#,Mvvm,Xamarin.forms,我尝试在我的xamarin表单中使用mvvm，但我仍然对每个页面中的导航有点困惑，我已经创建了界面和导航服务来处理xamarin表单中的所有导航，没有错误代码行，但是当我单击buton并尝试导航到其他页面时，它总是崩溃。这是我的一些代码 我的界面 namespace KGVC.Interfaces { public interface INavigationService { void NavigateToDashboard(); void Nav
namespace KGVC.Interfaces
{
public interface INavigationService
{
void NavigateToDashboard();
void NavigateToLogout();
void NavigateBack();
void gotoNews();
void goEvent();
void gotoKGCash();
void gotoCardCommnunity();
void gotoSetting();
void gotoNearbyLocation();
}
}
namespace KGVC.Services
{
public class NavigationService : INavigationService
{
public void goEvent()
{
var currentPage = GetCurrentPage();
currentPage.Navigation.PushAsync(new EventPage());
}
public void gotoCardCommnunity()
{
var currentPage = GetCurrentPage();
currentPage.Navigation.PushAsync(new CardCommunityPage());
}
public void gotoKGCash()
{
var currentPage = GetCurrentPage();
currentPage.Navigation.PushAsync(new KGCashPage());
}
public void gotoNearbyLocation()
{
var currentPage = GetCurrentPage();
currentPage.Navigation.PushAsync(new StoreMaps());
}
public void gotoNews()
{
var currentPage = GetCurrentPage();
currentPage.Navigation.PushAsync(new RssFeedView());
}
public void gotoSetting()
{
var currentPage = GetCurrentPage();
currentPage.Navigation.PushAsync(new SettingPages());
}
public void NavigateBack()
{
throw new NotImplementedException();
}
public void NavigateToDashboard()
{
var currentPage = GetCurrentPage();
Application.Current.MainPage = new MainPage();
}
public void NavigateToLogout()
{
var currentPage = GetCurrentPage();
Application.Current.MainPage = new NewPageLogin();
}
private Page GetCurrentPage()
{
var currentPage = Application.Current.MainPage.Navigation.NavigationStack.LastOrDefault();
return currentPage;
}
}
}
public class GridMenuViewModel
{
public ICommand gotoNews { get; private set; }
public ICommand goEvent { get; private set; }
public ICommand gotoKGCash { get; private set; }
public ICommand gotoSetting { get; private set; }
public ICommand gotoNearbyLocation { get; private set; }
public GridMenuViewModel()
{
gotoNews = new Command(() =>
{
var navigationService = new NavigationService();
navigationService.gotoNews();
});
goEvent = new Command(() =>
{
var navigationService = new NavigationService();
navigationService.goEvent();
});
gotoKGCash = new Command(() =>
{
var navigationService = new NavigationService();
navigationService.gotoKGCash();
});
gotoSetting = new Command(() =>
{
var navigationService = new NavigationService();
navigationService.gotoSetting();
});
gotoNearbyLocation = new Command(() =>
{
var navigationService = new NavigationService();
navigationService.gotoNearbyLocation();
});
}
}
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
NavigationPage.HasNavigationBar="True"
NavigationPage.BackButtonTitle="False"
BindingContext="{Binding GridMenuViewModel, Source={StaticResource Locator}}"
xmlns:control="clr-namespace:Xamarin.Forms;assembly=Xamarin.Forms.CarouselView"
xmlns:local="clr-namespace:KGVC.Views.MainPages"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="KGVC.Views.MainPages.GridMenu"
Title="HOME"
>
<ContentPage.Content>
<StackLayout >
<StackLayout BackgroundColor="##CEB053">
<StackLayout HeightRequest="35" BackgroundColor="##CEB053" Orientation="Horizontal">
<Label FontAttributes="Italic" TextColor="Black" Margin="9" Text="Hello," FontSize="15"/>
<Label TextColor="Black" Margin="9" Text="John Doe" FontSize="15" FontAttributes="Bold"/>
</StackLayout>
<StackLayout Padding="0" HeightRequest="30" BackgroundColor="#E3E6E3" Orientation="Horizontal">
<Image Margin="5" Source="ic_logo.png"/>
<Label Text="Points" Margin="5" FontSize="13" TextColor="Black"/>
</StackLayout>
</StackLayout>
<StackLayout HeightRequest="220" VerticalOptions="StartAndExpand">
<control:CarouselView HeightRequest="185" ItemsSource="{Binding MyDataSource}" Position="{Binding Position, Mode=TwoWay}">
<control:CarouselView.ItemTemplate>
<DataTemplate>
<Image Source="{Binding Image}"/>
</DataTemplate>
</control:CarouselView.ItemTemplate>
</control:CarouselView>
<local:CarouselIndicators IndicatorHeight="9" IndicatorWidth="9" UnselectedIndicator="unselected_circle.png" SelectedIndicator="selected_circle.png" Position="{Binding Position}" ItemsSource="{Binding MyDataSource}" />
</StackLayout>
<ScrollView IsClippedToBounds="True" VerticalOptions="StartAndExpand" Orientation="Vertical" >
<Grid x:Name="controlGrid" VerticalOptions="StartAndExpand" HeightRequest="370" Margin="15">
<Grid.RowDefinitions>
<RowDefinition Height="0" />
<RowDefinition Height="100" />
<RowDefinition Height="100" />
<RowDefinition Height="100" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="110" />
<ColumnDefinition Width="110" />
<ColumnDefinition Width="110" />
</Grid.ColumnDefinitions>
<StackLayout Orientation="Vertical" Grid.Row="1" Grid.Column="0" >
<Button Image="ic_account.png" Margin="5"
Style="{StaticResource plainButton}" />
<Label FontSize="12" Text="MY ACCOUNT" HorizontalOptions="Center"/>
</StackLayout>
<StackLayout Orientation="Vertical" Grid.Row="1" Grid.Column="1">
<Button Margin="5" Command="{Binding gotoCardCommunity}" Image="ic_card.png"
Style="{StaticResource plainButton}" />
<Label FontSize="12" Text="CARD" HorizontalOptions="Center"/>
</StackLayout>
<StackLayout Orientation="Vertical" Grid.Row="1" Grid.Column="2">
<Button Margin="5" Command="{Binding goEvent}" Image="ic_event"
Style="{StaticResource plainButton}" />
<Label FontSize="12" Text="PROMO" HorizontalOptions="Center"/>
</StackLayout>
<StackLayout Grid.Row="2" Grid.Column="0" Orientation="Vertical">
<Button Margin="5" Command="{Binding gotoNearbyLocation}" Image="ic_store"
Style="{StaticResource plainButton}" />
<Label FontSize="12" Text="STORE LOCATIONS" HorizontalOptions="Center"/>
</StackLayout>
<StackLayout Orientation="Vertical" Grid.Row="2" Grid.Column="1">
<Button Margin="5" Command="{Binding gotoNews}" Image="ic_news"
Style="{StaticResource plainButton}" />
<Label FontSize="12" Text="NEWS" HorizontalOptions="Center"/>
</StackLayout>
<StackLayout Grid.Row="2" Grid.Column="2" Orientation="Vertical">
<Button Margin="5" Command="{Binding gotoKGCash}" Image="ic_kgcash"
Style="{StaticResource plainButton}" />
<Label FontSize="12" Text="E-WALLET" HorizontalOptions="Center"/>
</StackLayout>
<StackLayout Orientation="Vertical" Grid.Row="3" Grid.Column="0">
<Button Margin="5" Image="ic_ecommerce"
Style="{StaticResource plainButton}" />
<Label FontSize="12" Text="E-COMMERCE" HorizontalOptions="Center"/>
</StackLayout>
<StackLayout Orientation="Vertical" Grid.Row="3" Grid.Column="1">
<Button Margin="5" Command="{Binding gotoSetting}" Image="ic_pointsummary.png"
Style="{StaticResource plainButton}" />
<Label FontSize="12" Text="POINT SUMMARY" HorizontalOptions="Center"/>
</StackLayout>
<StackLayout Orientation="Vertical" Grid.Row="3" Grid.Column="2">
<Button Margin="5" Command="{Binding gotoSetting}" Image="ic_setting"
Style="{StaticResource plainButton}" />
<Label FontSize="12" Text="SETTINGS" HorizontalOptions="Center"/>
</StackLayout>
</Grid>
</ScrollView>
</StackLayout>
</ContentPage.Content>
</ContentPage>
我已经尝试将导航服务更改为使用pushmodalasync，使导航异步但仍然崩溃，有人可以帮助我吗？我没有使用prism、mvvmlight和其他第三方mvvm nuget，这取决于您的
主页。您是否检查了GetCurrentPage（）
是否确实返回了一些内容
尝试将GetCurrentPage（）
更改为：
Page GetCurrentPage() =>
Application.Current.MainPage.Navigation?.NavigationStack?.LastOrDefault() ??
Application.Current.MainPage;
我发现的另一个问题：
1.与Java不同。方法名称应以大写字母开头。目前你有一个纯混合
2.在XAML中初始化BindingContext
，由于出现错误，将创建ViewModel
两次。将其更改为：
<ContentPage
xmlns:vm="your-namespace.vm"
...>
<ContentPage.BindingContext>
<vm:GridMenuViewModel />
</ContentPage.BindingContext>
</ContentPage>
检查上面的列表，注意应用程序输出和异常情况。thaks对于您的答案，它已经在使用GetCurrentPage方法工作，并将PushAsync更改为PushModalAsync及其工作，但当im尝试使用PushAsync im using application.Current.MainPage=new MainPage（）时，它不工作；在我的主页，这是因为登录后，我不希望我的用户可以再次回到登录页面。这就是我不能使用异步推送的原因吗？更新了我的答案。很可能是因为您没有等待异步代码执行。另外请注意建议#5。我已经更改了代码，以便使用此应用程序在NavigationPage中创建主页。Current.MainPage=new NavigationPage（new MainPage（））；它可以执行pushasync，但只能执行一次，在导航到其他页面后，返回到mainpage并再次导航到其他页面后，它将强制关闭，整个mvvm的想法仍然让我困惑，mvvm是创建企业应用程序所必需的吗？有什么例外？关于MVVM检查此线程：异常为“未处理的异常发生”。我已尝试在导航服务中设置断点，但它不会中断模式
<StackLayout BackgroundColor="##CEB053">
public async Task GoToCardCommnunity()
{
var currentPage = GetCurrentPage();
await currentPage.Navigation.PushAsync(new CardCommunityPage());
}