Xamarin从视图模型到列表视图数据模板中的按钮的Forms绑定命令 [英] Xamarin Forms Binding Command from View Model to Button in List View Data Template
问题描述
我正在使用Xamarin.Forms 2.4构建社交帖子共享应用程序,并且它与我的API通讯.
I am building social post sharing application using Xamarin.Forms 2.4 and it talks to my API.
我有PostsPage,它使用PostDataViewModel将ObservableCollection加载到PostsPage中定义的ListView中.列表视图的数据模板指向视图文件.但是,在Post View模板中,我可以绑定到我的帖子模型"的各个属性,但是无法绑定到ViewModel上存在的command.我没有运气就尝试了x:Reference.
I have PostsPage which uses PostDataViewModel to load ObservableCollection to ListView defined in PostsPage. Data template of list views points to view file. However, in Post View Template I can bind to individual properties of My Post Model, but binding to command, which exists on ViewModel doesn't work. I tried x:Reference with no luck.
我的模特:
using System;
using System.Collections.Generic;
namespace SOD_APP_V2.Model
{
public class PostDataModel
{
public string ID { get; set; }
public string Title { get; set; }
public string Message { get; set; }
public string Image { get; set; }
public string SocialMedia { get; set; }
public string AvailableTime { get; set; }
public string Audiences { get; set; }
public string Topics { get; set; }
public List<PostVersion> Versions { get; set; }
public PostDataModel PostDetails
{
get
{
return this;
}
}
}
public class PostVersion
{
public string SocialMediaID { get; set; }
public string IconPath { get; set; }
public int CharacterCount { get; set; }
public string Message { get; set; }
}
}
我的视图模型:
namespace SOD_APP_V2.ViewModel
{
public class PostDataViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
//Bindable properties
public ObservableCollection<PostDataModel> PostDataCollection { get; set; }
public ICommand LoadMorePostsCommand { get; private set; }
public ICommand RejectPostCommand { get; private set; }
public static JObject SocialmediaSites { get; set; }
public object SelectedItem { get; set; }
bool isLoadMoreEnabled;
public bool IsLoadMoreEnabled
{
get
{
return isLoadMoreEnabled;
}
set
{
if (isLoadMoreEnabled != value)
{
isLoadMoreEnabled = value;
OnPropertyChanged((nameof(IsLoadMoreEnabled)));
}
}
}
string pageTitle;
public string PageTitle
{
get
{
return pageTitle;
}
set
{
if (pageTitle != value)
{
pageTitle = value;
OnPropertyChanged(nameof(PageTitle));
}
}
}
int currentPage = 1;
public int CurrentPage
{
get
{
return currentPage;
}
set
{
if(currentPage != value)
{
currentPage = value;
OnPropertyChanged(nameof(CurrentPage));
}
}
}
public PostDataViewModel()
{
PostDataCollection = new ObservableCollection<PostDataModel>();
SocialmediaSites = default(JObject);
IsLoadMoreEnabled = true;
LoadMorePostsCommand =
new Command(async () => await GetPosts(), () => IsLoadMoreEnabled);
RejectPostCommand = new Command<PostDataModel>((post) =>
{
System.Diagnostics.Debug.WriteLine("Reject command executed");
System.Diagnostics.Debug.WriteLine("Post ID: " + post.ID);
});
string deployment = ConfigController.GetDeploymentName(ApiController.DeploymentDomain);
MessagingCenter.Subscribe<PostsPage, JArray>(this, "translations", (sender, arg) => {
PageTitle = (arg[0].ToString() != "") ? arg[0].ToString() : "Posts from " + deployment;
});
if (deployment != null)
{
//TODO: lang packs
PageTitle = "Posts from " + deployment;
}
}
public async Task<bool> GetPosts()
{
...
}
protected virtual void OnPropertyChanged(String propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(nameof(propertyName)));
}
}
}
}
我的帖子页面XAML:
My Post Page XAML:
<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:SOD_APP_V2"
xmlns:view="clr-namespace:SOD_APP_V2.View;assembly=SOD_APP_V2"
xmlns:viewModel="clr-namespace:SOD_APP_V2.ViewModel;assembly=SOD_APP_V2"
xmlns:controls="clr-namespace:SOD_APP_V2.Controls;assembly=SOD_APP_V2"
x:Class="SOD_APP_V2.PostsPage" x:Name="PostsPage"
>
<ContentPage.BindingContext>
<viewModel:PostDataViewModel/>
</ContentPage.BindingContext>
<ContentPage.Content>
<StackLayout>
<StackLayout Orientation="Vertical" Padding="10, 5, 10, 5">
<Label x:Name="titleLabel" Text="{Binding PageTitle}"
VerticalOptions="Start"
HorizontalTextAlignment="Center"
VerticalTextAlignment="Center"
BackgroundColor="Transparent"
HorizontalOptions="CenterAndExpand" />
<controls:InfiniteListView x:Name="listView"
SelectedItem="{Binding SelectedItem,Mode=TwoWay}"
IsLoadMoreItemsPossible="{Binding IsLoadMoreEnabled}"
LoadMoreInfiniteScrollCommand="{Binding LoadMorePostsCommand}"
IsEnabled="true"
IsBusy="{Binding IsBusy}"
HasUnevenRows="true"
ItemsSource="{Binding PostDataCollection}"
SeparatorVisibility="None">
<controls:InfiniteListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<view:PostViewTemplate/>
</ViewCell>
</DataTemplate>
</controls:InfiniteListView.ItemTemplate>
</controls:InfiniteListView>
</StackLayout>
<StackLayout HorizontalOptions="FillAndExpand"
VerticalOptions="End">
<Label x:Name="infoLabel" Text="test"
Opacity="0"
TextColor="White"
BackgroundColor="#337ab7"
HorizontalTextAlignment="Center">
</Label>
</StackLayout>
</StackLayout>
</ContentPage.Content>
最后,我的Post View模板描述了每个帖子:
And Finally my Post View template describing each post:
<?xml version="1.0" encoding="UTF-8"?>
<ContentView xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:model="clr-namespace:SOD_APP_V2.Model;assembly=SOD_APP_V2"
xmlns:controls="clr-namespace:SOD_APP_V2.Controls;assembly=SOD_APP_V2"
x:Class="SOD_APP_V2.View.PostViewTemplate">
<ContentView.Resources>
<ResourceDictionary>
<Style TargetType="controls:AwesomeButton">
<Setter Property="BorderWidth" Value="1"/>
<Setter Property="TextColor" Value="White"/>
<Setter Property="BorderRadius" Value="7"/>
<Setter Property="FontFamily" Value="FontAwesome"/>
</Style>
</ResourceDictionary>
</ContentView.Resources>
<ContentView.Content>
<Frame HasShadow="false" CornerRadius="5" IsClippedToBounds="true" OutlineColor="#09478e" Padding="0" Margin="10">
<Grid
Padding="0">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="1" />
<ColumnDefinition Width="1" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="1" />
<ColumnDefinition Width="1" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="50"></RowDefinition>
<RowDefinition Height="50"></RowDefinition>
<RowDefinition Height="1"></RowDefinition>
<RowDefinition Height="100"></RowDefinition>
<RowDefinition Height="1"></RowDefinition>
<RowDefinition Height="40"></RowDefinition>
<RowDefinition Height="40"></RowDefinition>
<RowDefinition Height="1"></RowDefinition>
</Grid.RowDefinitions>
<StackLayout Orientation="Horizontal" Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="6" BackgroundColor="#B0C4DB" Padding="5">
<Label x:Name="postTitle" Text="{Binding Title}" TextColor="#09478e" HorizontalOptions="CenterAndExpand" VerticalOptions="CenterAndExpand"/>
<StackLayout Orientation="Horizontal" VerticalOptions="CenterAndExpand" HorizontalOptions="End">
<controls:AwesomeButton Clicked="OnAvailableTimePopupClicked" CommandParameter="{Binding AvailableTime}" Text="" TextColor="#09478e" BorderWidth="0" Margin="-5" BackgroundColor="Transparent" WidthRequest="36" FontSize="24"></controls:AwesomeButton>
<controls:AwesomeButton Clicked="OnAudiencesPopupClicked" CommandParameter="{Binding Audiences}" Text="" TextColor="#09478e" BorderWidth="0" Margin="-5" BackgroundColor="Transparent" WidthRequest="36" FontSize="24"></controls:AwesomeButton>
<controls:AwesomeButton Clicked="OnTopicsPopupClicked" CommandParameter="{Binding Topics}" Text="" TextColor="#09478e" BorderWidth="0" Margin="-5" BackgroundColor="Transparent" WidthRequest="36" FontSize="24"></controls:AwesomeButton>
</StackLayout>
</StackLayout>
<controls:RepeaterView Grid.Row="1" Grid.Column="2"
ItemsSource="{Binding Versions}"
NoOfColumns="3"
>
<controls:RepeaterView.ItemTemplate>
<DataTemplate>
<StackLayout Spacing="0" >
<Label Text="{Binding Message}" IsVisible="false"/>
<Image Source="{Binding IconPath}">
<Image.GestureRecognizers>
<TapGestureRecognizer
Tapped="OnMessageVersionClicked"
NumberOfTapsRequired="1" />
</Image.GestureRecognizers>
</Image>
</StackLayout>
</DataTemplate>
</controls:RepeaterView.ItemTemplate>
</controls:RepeaterView>
<Image BackgroundColor="White" Grid.Row="3" Grid.Column="2" Source="{Binding Image}" VerticalOptions="FillAndExpand"/>
<Label x:Name="postMessage" BackgroundColor="White" Grid.Row="3" Grid.Column="3" Text="{Binding Message}" TextColor="#09478e" VerticalOptions="FillAndExpand" />
<controls:AwesomeButton Clicked="OnSharePostClicked" CommandParameter="{Binding ID}" BackgroundColor="#5cb85c" Grid.Row="5" Grid.Column="2" Text=" Share" BorderColor="#5cb85c"></controls:AwesomeButton>
<controls:AwesomeButton Clicked="OnSchedulePostClicked" CommandParameter="{Binding ID}" BackgroundColor="#5bc0de" Grid.Row="5" Grid.Column="3" Text=" Schedule" BorderColor="#5bc0de"></controls:AwesomeButton>
<controls:AwesomeButton Clicked="OnEditPostClicked" CommandParameter="{Binding PostDetails}" TextColor="#09478e" BackgroundColor="White" Grid.Row="6" Grid.Column="2" Text=" Edit" BorderColor="#09478e"></controls:AwesomeButton>
<controls:AwesomeButton Command="{Binding Path=DataContext.RejectPostCommand}" CommandParameter="{Binding}" BackgroundColor="#d9534f" Grid.Row="6" Grid.Column="3" Text=" Reject" BorderColor="#d9534f"></controls:AwesomeButton>
<!-- Inner Border -->
<BoxView Grid.Row="2" Grid.RowSpan="3" Grid.Column="1" BackgroundColor="#09478e"></BoxView>
<BoxView Grid.Row="2" Grid.RowSpan="3" Grid.Column="4" BackgroundColor="#09478e"></BoxView>
<BoxView Grid.Column="1" Grid.ColumnSpan="4" Grid.Row="2" BackgroundColor="#09478e"></BoxView>
<BoxView Grid.Column="1" Grid.ColumnSpan="4" Grid.Row="4" BackgroundColor="#09478e"></BoxView>
</Grid>
</Frame>
</ContentView.Content>
正如您在后视图模板"中所看到的,我试图在ViewModel中绑定RejectPostCommand,但它没有绑定.我尝试了x:References to PostsPage,但它使我感到异常,因为它无法从我的视图模板中找到该Page.我需要能够以某种方式访问命令.会有任何想法吗?
As you see in Post View Template, I am trying to bind RejectPostCommand in ViewModel, but it doesn't bind. I tried x:Reference to PostsPage, but it threw me exception, as it couldn't find that Page from my View Template. I need to able to access command somehow. Would anybody have any ideas?
推荐答案
将PostViewTemplate XAML移入PostsPage可能已经奏效,但是现在您没有可重用的模板.
Moving PostViewTemplate XAML into PostsPage may have worked, but now you do not have a re-usable template.
您可以通过对原始代码进行以下3次小的更改来创建可重用的解决方案.
You can create a re-usable solution with the following 3 minor changes to your original code.
向您的PostViewTemplate代码后面添加可绑定属性,如下所示:
Add a bindable property to your PostViewTemplate code-behind like so:
public static BindableProperty ParentBindingContextProperty =
BindableProperty.Create(nameof(ParentBindingContext), typeof(object),
typeof(PostViewTemplate), null);
public object ParentBindingContext
{
get { return GetValue(ParentBindingContextProperty); }
set { SetValue(ParentBindingContextProperty, value); }
}
将该属性绑定到PostsPage XAML中的ViewModel中,如下所示:
Bind that property to the ViewModel in your PostsPage XAML like so:
<view:PostViewTemplate ParentBindingContext="{Binding Source={x:Reference Home}, Path=BindingContext}"/>
现在,您可以直接从PostViewTemplate中的绑定访问父"视图模型,例如(注意,您需要在ContentView中添加x:Name才能用作您的Source绑定):
Now you can access your "parent" viewmodel directly from the bindings in your PostViewTemplate, like this (Note that you need to add an x:Name to your ContentView to use as the source of your binding):
<ContentView ... x:Name="PostView" ...>
<controls:AwesomeButton BindingContext="{Binding Source={x:Reference PostView}, Path=ParentBindingContext}" Command="{Binding OnTopicsPopupClicked}" CommandParameter="{Binding Topics}" Text="" TextColor="#09478e" BorderWidth="0" Margin="-5" BackgroundColor="Transparent" WidthRequest="36" FontSize="24"></controls:AwesomeButton>
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