Switch templates in xamarin based of bound property (NOT ItemTemplate)

问题

I have a Model that contains some data, and a field that can have one of three (enum) values.

Socket,
Tcp,
Udp

And a View that shows some details.
The details that I want shown in the view differ according to the value of this property in the model.

I have read all about ItemTemplates for Lists and Pickers, and I want to do something similar but just with a single view bound to a single property.

If Socket => Show this view else => Show this other view.

Both views have the same viewmodel.

View

<ContentView.Resources>
    <local:SocketServerSocketView x:Key="ServerSocket" />
    <local:SocketServerTcpUdpView x:Key="ServerTcpUdp" />
</ContentView.Resources>

...

<ContentView Grid.Column="2" Margin="12" >
    <ContentView.Content>
        <local:SocketServerTcpUdpView />
    </ContentView.Content>
    <ContentView.Style>
        <Style TargetType="ContentView">
            <Style.Triggers>
                <DataTrigger TargetType="{x:Type ContentView}" Binding="{Binding Mode}"  Value="{Binding models:NetworkMode.Socket}">
                    <Setter Property="Content" Value="{StaticResource ServerSocket}" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </ContentView.Style>
</ContentView>

So I start (by default) displaying the TCP version, and want to dynamically switch it out for the socket template when the value of the enum changes. What am I doing wrong?

回答1:

We can refer to Data Triggers documents to know how to achieve that .

Create a sample ViewModel model only contains Model property inside it .

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private int model;

    public int Model
    {
        set
        {
            if (model != value)
            {
                model = value;
                OnPropertyChanged("Model");
            }
        }
        get
        {
            return model;
        }
    }

    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

Then we can create two sample ContentView to replace SocketServerSocketView and SocketServerTcpUdpView as follow : SocketServerTcpUdpView：

<?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:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             mc:Ignorable="d"
             x:Class="AppTriggerType.SocketServerTcpUdpView">
  <ContentView.Content>
      <StackLayout BackgroundColor="Azure">
            <Label Text="SocketServer TcpUdpView!"
                   VerticalOptions="Center" />
      </StackLayout>
  </ContentView.Content>
</ContentView>

SocketServerSocketView：

<?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:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             mc:Ignorable="d"
             x:Class="AppTriggerType.SocketServerSocketView">
  <ContentView.Content>
      <StackLayout BackgroundColor="Beige" >
            <Label Text="SocketServer SocketView!" />
      </StackLayout>
  </ContentView.Content>
</ContentView>

Now in Xaml of ContentPage ,we can defined as follow :

<?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:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:local="clr-namespace:AppTriggerType"
             mc:Ignorable="d"
             x:Class="AppTriggerType.MainPage">


    <ContentPage.Resources>
            <local:SocketServerSocketView x:Key="ServerSocket" />
            <local:SocketServerTcpUdpView x:Key="ServerTcpUdp" />
    </ContentPage.Resources>
    
    <StackLayout>
        <!-- Place new controls here -->
        <Label Text="Welcome to Xamarin.Forms!" 
           HorizontalOptions="Center"
           VerticalOptions="Start" />
        <Button Text="ServerSocket"
                Clicked="Button_Clicked_ServerSocket"/>
        <Button Text="ServerTcpUdp"
                Clicked="Button_Clicked_ServerTcpUdp"/>
        <ContentView x:Name="MyContentView"
                     Margin="12"
                     VerticalOptions="FillAndExpand">
            <ContentView.Content>
                <ContentView />
            </ContentView.Content>
            <ContentView.Triggers>
                <DataTrigger TargetType="{x:Type ContentView}"
                             Binding="{Binding Source={x:Reference MyContentView}, Path=BindingContext.Model}"
                             Value="1">
                    <Setter Property="Content"
                            Value="{StaticResource ServerSocket}" />
                </DataTrigger>
                <DataTrigger TargetType="{x:Type ContentView}"
                             Binding="{Binding Source={x:Reference MyContentView}, Path=BindingContext.Model}"
                             Value="2">
                   <Setter Property="Content"
                            Value="{StaticResource ServerTcpUdp}" />
                </DataTrigger>
            </ContentView.Triggers>
        </ContentView>
    </StackLayout>
</ContentPage>

Last bind data for MyContentView in ContentPage.xaml.cs :

public partial class MainPage : ContentPage
{
    ViewModel viewModel = new ViewModel();
    public MainPage()
    {
        InitializeComponent();
        viewModel.Model = 1;
        MyContentView.BindingContext = viewModel;
    }

    private void Button_Clicked_ServerSocket(object sender, EventArgs e)
    {
        viewModel.Model = 1;
    }

    private void Button_Clicked_ServerTcpUdp(object sender, EventArgs e)
    {
        viewModel.Model = 2;
    }
}

Now we will see the effect as follow :

Here is the sample.

来源：https://stackoverflow.com/questions/63058029/switch-templates-in-xamarin-based-of-bound-property-not-itemtemplate