How to use devaxpress WPF to create the first MVVM application in winui?

In this paper , We will describe how to create from scratch WinUI MVVM Applications , And show in the process DevExpress WinUI MVVM The powerful functions of the framework .

first , The official technical team is WPF The platform created MVVM frame , Later, I found that the technology developed in this framework can be easily used in WinForms Use in , So migrate the framework there . stay v22.1 in , Official team for WinUI To optimize the MVVM frame , Keep the core functionality intact , If you use our WPF or WinForms Control , Migrating to WinUI I don't have any problems with it .

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Let's start by creating a bare view model , You can select the following view model types ：

1. View model generated at compile time
2. ViewModelBase -  Descendant view model
3. have INotifyPropertyChanged  Interface implementation of simple classes

The first option used in this article , Because it keeps your view model code clean 、 compact , And help avoid spelling mistakes .

take DevExpress.Mvvm.CodeGenerators and DevExpress.WinUI NuGet Add packages to your project , After adding the package, create a view model class and put GenerateViewModel Attribute assigned to it ：

using DevExpress.Mvvm.CodeGenerators;

[GenerateViewModel]
public partial class MainViewModel {
[GenerateProperty]
string userName;

[GenerateCommand]
void Register() {
Debug.WriteLine($"{UserName} was successfully registered!");
}
}

Please note that , You need to make the class partial and add DevExpress.Mvvm.CodeGenerators Namespace .

At compile time, the generator will automatically create a INotifyPropertyChanged Supported view model counterparts ：

partial class MainViewModel : INotifyPropertyChanged {
public event PropertyChangedEventHandler? PropertyChanged;

protected void RaisePropertyChanged(PropertyChangedEventArgs e) => PropertyChanged?.Invoke(this, e);

public string? UserName {
get => userName;
set {
if(EqualityComparer.Default.Equals(userName, value)) return;
userName = value;
RaisePropertyChanged(UserNameChangedEventArgs);
}
}
DelegateCommand? registerCommand;
public DelegateCommand RegisterCommand => registerCommand ??= new DelegateCommand(Register, null);
static PropertyChangedEventArgs UserNameChangedEventArgs = new PropertyChangedEventArgs(nameof(UserName));
}

You can view the generated classes in the project ：Dependencies -> Analyzers -> DevExpress.Mvvm.CodeGenerators -> DevExpress.Mvvm.CodeGenerators.ViewModelGenerator -> MainViewModel.g.cs

 

take CanRegister Method is added to your view model to determine when Register command . Please note that ,WinUI Command not to use CommandManager, So you need to use RaiseCanExecuteChanged Manually refresh CanExecute state ：

public partial class MainViewModel {
//...
void OnUserNameChanged() {
RegisterCommand.RaiseCanExecuteChanged();
}
bool CanRegister() => !string.IsNullOrEmpty(UserName);
}

The code generator will automatically OnUserNameChanged and CanRegister Merge into UserName Properties and Register In command .

The view model has a for storing user names UserName Properties and registered users RegisterCommand Method , Create a simple UI To use the view model , Add a... To the main window TextBox And a Button And bind them to the properties and commands of the view model ：

<StackPanel>
<TextBox Text="{x:Bind ViewModel.UserName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
<Button Content="Register" Command="{x:Bind ViewModel.RegisterCommand}"/>
</StackPanel>

You may have noticed , In this article, I used x:Bind  replace Binding,x:Bind yes UWP A relatively new markup extension introduced in . It uses type information at compile time to optimize binding , So it's best to use it as much as possible . Use... In windows or user controls x:Bind when , The default binding source is the window itself , Therefore, you need to define the view model as a window property ：

public sealed partial class MainWindow : Window {
public MainViewModel ViewModel { get; } = new MainViewModel();
public MainWindow() {
this.InitializeComponent();
}
}

Now simply MVVM The application can send information from the view to the view model and execute the commands of the view model , Expand it to allow users to click Register Button to display a message box . Use UI service , Visual elements can be accessed without directly from the view model , This will help us keep clean MVVM Pattern . take MessageBoxService Add to the view and ServiceClient Property is bound to your view model ：

<Window ...
xmlns:dxc="using:DevExpress.WinUI.Core">
<StackPanel>
<dxc:Interaction.Behaviors>
<dxc:MessageBoxService ServiceClient="{x:Bind ViewModel}"/>
</dxc:Interaction.Behaviors>
<TextBox Text="{x:Bind ViewModel.UserName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
<Button Content="Register" Command="{x:Bind ViewModel.RegisterCommand}"/>
</StackPanel>
</Window>

then , take ImplementISupportUIServices Parameters added to GenerateViewModel Properties and in Register Method used in MessageBoxService：

using DevExpress.Mvvm;
using DevExpress.Mvvm.CodeGenerators;

[GenerateViewModel(ImplementISupportUIServices = true)]
public partial class MainViewModel {
[GenerateProperty]
string userName;
IMessageBoxService MessageBoxService { get => ServiceContainer.GetService<IMessageBoxService>(); }
[GenerateCommand]
void Register() {
MessageBoxService.ShowAsync($"{UserName} was successfully registered!", "Registration");
}
}

Now? , When the user clicks the button, he will see a message box . Please note that , Your view model does not directly access any visual elements , Instead, the service mechanism is used as the middle tier .

Let's press Enter Key Register Commands to enhance the user experience ,WinUI The button doesn't have IsDefault attribute , Therefore, it is necessary to handle the key event to capture the press Enter The moment of . but MVVM The kit has KeyToCommand Behavior , The command can be invoked when the specified key is used . take KeyToCommand Add behavior to Interaction.Behaviors Set merge to set its KeyGesture and Command attribute ：

<StackPanel>
<dxc:Interaction.Behaviors>
<dxc:KeyToCommand KeyGesture="Enter" Command="{x:Bind ViewModel.RegisterCommand}"/>
<!--...-->
</dxc:Interaction.Behaviors>
<!--...-->
</StackPanel>

KeyToCommand Is an operation that can be used immediately , But you can easily create custom behaviors as needed , To avoid writing similar code hiding in different views .

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