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Reputation: 23859

Why the Application class in UWP project has a constructor but the Application class of WPF project does not?

As shown below, I noticed that when you create a UWP project in VS2019, it creates a constructor public App(){....} in the application class App.xaml.cs of the project. That constructor then can be used to call (for example) methods of a .NET Standard Class Library project in the same solution as shown in the second code block here.

But, as shown below, the application class App.xaml.cs of WPF project does not have such a constructor created by default.

Question Can I just manually create a constructor public App(){....} in the application class App.xaml.cs of a WPF project and call a method of a .NET standard class library from there or it may cause an issues later on?

The App.xaml.cs of UWP project:

using System;
using System.IO;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
......

namespace Test_UWP_Project
{
    /// <summary>
    /// Provides application-specific behavior to supplement the default Application class.
    /// </summary>
    sealed partial class App : Application
    {
        /// <summary>
        /// Initializes the singleton application object.  This is the first line of authored code
        /// executed, and as such is the logical equivalent of main() or WinMain().
        /// </summary>
        public App()
        {
            this.InitializeComponent();
            this.Suspending += OnSuspending;
        }
..........
............
}

The App.xaml.cs of WPF project:

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Windows;
.....
.....

namespace Test_WPF_Project
{
    /// <summary>
    /// Interaction logic for App.xaml
    /// </summary>
    public partial class App : Application
    {
    }
}

Upvotes: 0

Views: 348

Answers (2)

mm8
mm8

Reputation: 169320

Can I just manually create a constructor public App(){....} in the application class App.xaml.cs of a WPF project and call a method of a .NET standard class library from there or it may cause an issues later on?

Yes, you can. As mentioned in the docs, if you don't provide a constructor for your class, C# creates one by default that instantiates the object and sets member variables to the default values. So whenever you want some custom initialization logic, you should define your own constructor.

Depending on what you want to do, it may be a better option to override the OnStartup method of the App class instead of creating a constructor though:

public partial class App : Application
{
    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);
        //your code here...
    }
}

Upvotes: 1

Keith Stein
Keith Stein

Reputation: 6744

I've never used an application constructor in WPF, but a quick test shows that you can add a constructor to App.xaml.cs and it will work just like any other class. Alternatively, you could also handle the Application.StartUp event. I don't know of any reason why you wouldn't be able to call just about anything from these methods.

Upvotes: 1

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