Add Message Service

10 minute read

Objective

I want to:

Show Confirmation message to user before deleting browsed file.
After deleting file, show information message to user.
We will continue from previous article 🚀 Delete Browse Solidworks Document File.

Demo Video

Below 🎬 video shows how to Add Message Service in Visual Studio 2022.

Add Service for Messaging in application

Now we add MessagesService class to “Service” folder.
Please see below 👇🏻 image for reference.

For reference, how to add Service class, please visit 🚀 Add Service for Browsing File Dialog article.

Now we will add following services to this newly created MessagesService class.

ConfirmationMessagesService
InformationMessagesService
ErrorMessagesService

Please see below 👇🏻 image for reference.

Please see below 👇🏻 code sample for reference.

using Prism.Events;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace WPF_Application.Services
{
    internal class ConfirmationMessagesService : PubSubEvent<string> { }
    internal class InformationMessagesService : PubSubEvent<string> { }
    internal class ErrorMessagesService : PubSubEvent<string> { }
}

For more details on how to add Services, please visit 🚀 Add Service for Browsing File Dialog article.
In above line, we add <string> to all PubSubEvent class.
This indicate that, when we Publish our service, we need to give a string as passing parameter to Publish service.
For example, we will pass a question as string when we Publish ConfirmationMessagesService service.

Register Services

Open MainWindow.xaml.cs file.
Pass IEventAggregator to constructor, and assigned it to private field.
Please see below 👇🏻 image for reference.

Please see below 👇🏻 code sample for reference.

using Microsoft.Win32;
using Prism.Events;
using Syncfusion.Windows.Shared;
using System;
using System.Windows;
using WPF_Application.Services;
using WPF_Application.ViewModels;

namespace WPF_Application.Views
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : ChromelessWindow
    {
        private readonly IEventAggregator eventAggregator;

        public MainWindow(IEventAggregator eventAggregator)
        {
            InitializeComponent();
            this.eventAggregator = eventAggregator;
        }
    }
}

Now, we register our services.
When these service is called, some functions will gets executed.
These registration and execution is handle by eventAggregator field.
Please see below 👇🏻 code sample for reference.

using Microsoft.Win32;
using Prism.Events;
using Syncfusion.Windows.Shared;
using System;
using System.Windows;
using WPF_Application.Services;
using WPF_Application.ViewModels;

namespace WPF_Application.Views
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : ChromelessWindow
    {
        private readonly IEventAggregator eventAggregator;

        public MainWindow(IEventAggregator eventAggregator)
        {
            InitializeComponent();
            this.eventAggregator = eventAggregator;
            this.eventAggregator.GetEvent<BrowseFileDialogService>().Subscribe(BrowseFile);
            this.eventAggregator.GetEvent<ConfirmationMessagesService>().Subscribe(ConfirmationMessages);
            this.eventAggregator.GetEvent<InformationMessagesService>().Subscribe(InformationMessages);
            this.eventAggregator.GetEvent<ErrorMessagesService>().Subscribe(ErrorMessages);
        }

        private void BrowseFile()
        {
            OpenFileDialog openFileDialog = new OpenFileDialog();
            openFileDialog.Filter = "Solidworks Part|*.sldprt|Solidworks Assembly|*.sldasm|Solidworks Drawing|*.slddrw";
            openFileDialog.DefaultExt = "*.sldprt";

            bool? result = openFileDialog.ShowDialog();

            if (result == false || string.IsNullOrEmpty(openFileDialog.FileName))
                return;

            var viewModel = DataContext as MainWindowViewModel;
            viewModel.FilePath = openFileDialog.FileName;
        }

        private void ConfirmationMessages(string messageToShow)
        {
            var result = MessageBox.Show(messageToShow, "Confirmation", MessageBoxButton.YesNo, MessageBoxImage.Question);
            var viewModel = DataContext as MainWindowViewModel;
            viewModel.DeleteFile = (result == MessageBoxResult.Yes) ? true : false;
        }

        private void InformationMessages(string messageToShow)
        {
            MessageBox.Show(messageToShow, "Information", MessageBoxButton.OK, MessageBoxImage.Information);
        }

        private void ErrorMessages(string messageToShow)
        {
            MessageBox.Show(messageToShow, "Error", MessageBoxButton.OK, MessageBoxImage.Error);
        }
    }
}

Understand Service Methods

In above code, we register 4 services. They are as follows:
- BrowseFileDialogService
- ConfirmationMessagesService
- InformationMessagesService
- ErrorMessagesService
BrowseFileDialogService is already explained in 🚀 Understand Service Call Execute Function article.
Please visit 🚀 Understand Service Call Execute Function article for more details.
In this section, we will understand remaining 3 service and their respective execution methods.

Understand `ConfirmationMessages` method

In MainWindow.xaml.cs contructor, we register ConfirmationMessagesService service.
When we call for ConfirmationMessagesService service, we execute ConfirmationMessages method.
Now let us understand ConfirmationMessages method as follows.

private void ConfirmationMessages(string messageToShow)
{
    var result = MessageBox.Show(messageToShow, "Confirmation", MessageBoxButton.YesNo, MessageBoxImage.Question);
    var viewModel = DataContext as MainWindowViewModel;
    viewModel.DeleteFile = (result == MessageBoxResult.Yes) ? true : false;
}

In ConfirmationMessages method, we pass a string as parameter.
- Parameter Name: messageToShow
- Variable Type: string
- Return Type: Void

var result = MessageBox.Show(messageToShow, "Confirmation", MessageBoxButton.YesNo, MessageBoxImage.Question);

In above line, we create a variable as follows:
- Variable Name: result
- Variable Type: var
In above line, we store result of MessageBox.Show method into result variable.

This MessageBox.Show method takes following parameters.

messageBoxText: A String that specifies the text to display.
caption: A String that specifies the title bar caption to display.

button: A MessageBoxButtons values that specifies which buttons to display in the message box. These buttons are as follows.

Member	Description
AbortRetryIgnore	`2: The message box contains Abort, Retry, and Ignore buttons.`
CancelTryContinue	`6: Specifies that the message box contains Cancel, Try Again, and Continue buttons.`
OK	`0: The message box contains an OK button.`
OKCancel	`1: The message box contains OK and Cancel buttons.`
RetryCancel	`5: The message box contains Retry and Cancel buttons.`
YesNo	`4: The message box contains Yes and No buttons.`
YesNoCancel	`3: The message box contains Yes, No, and Cancel buttons.`

icon: A MessageBoxImage value that specifies the icon to display. These buttons are as follows.

Member	Description
Asterisk	`64: The message box contains a symbol consisting of a lowercase letter i in a circle.`
Error	`16: The message box contains a symbol consisting of white X in a circle with a red background.`
Exclamation	`48: The message box contains a symbol consisting of an exclamation point in a triangle with a yellow background.`
Hand	`16: The message box contains a symbol consisting of white X in a circle with a red background.`
Information	`64: The message box contains a symbol consisting of a lowercase letter i in a circle.`
None	`0: The message box contains no symbols.`
Stop	`16: The message box contains a symbol consisting of white X in a circle with a red background.`
Warning	`48: The message box contains a symbol consisting of an exclamation point in a triangle with a yellow background.`

Result Value: This MessageBox.Show method return MessageBoxResult value that specifies which message box button is clicked by the user as follows.

Member	Description
Cancel	`2: The result value of the message box is Cancel.`
No	`7: The result value of the message box is No.`
None	`0: The message box returns no result.`
OK	`1: The result value of the message box is OK.`
Yes	`6: The result value of the message box is Yes.`

Parameter values we used in our code are as follows:

Parameter Name	Value Used
messageBoxText	`messageToShow`
caption	`"Confirmation"`
button	`MessageBoxButton.YesNo`
icon	`MessageBoxImage.Question`

Please visit 🚀 MessageBox.Show Method article for more details.

var viewModel = DataContext as MainWindowViewModel;

In above line of code, we create a variable as follows:
- Variable Name: viewModel
- Variable Type: MainWindowViewModel
- Value: DataContext property of MainWindow.

viewModel.DeleteFile = (result == MessageBoxResult.Yes) ? true : false;

In above line, we set the value of DeleteFile property.
This property is part of viewModel variable.

Please note that we still not created this propery, so Visual studio will show error.

We set the value of DeleteFile property to true or false, based on condition.
- Condition: (result == MessageBoxResult.Yes)
- If above condition is true, then final value is true.
- If above condition is false, then final value is false.

Understand `InformationMessages` method

Now let us understand InformationMessages method as follows.

private void InformationMessages(string messageToShow)
{
    MessageBox.Show(messageToShow, "Information", MessageBoxButton.OK, MessageBoxImage.Information);
}

In above line of code, we show a MessageBox to user.
For this, we use MessageBox.Show method.
For more details on MessageBox.Show method please read previous section of this article.
Parameter values we used in our code are as follows:

Parameter Name	Value Used
messageBoxText	`messageToShow`
caption	`"Information"`
button	`MessageBoxButton.OK`
icon	`MessageBoxImage.Information`

Understand `ErrorMessages` method

Now let us understand ErrorMessages method as follows.

private void ErrorMessages(string messageToShow)
{
    MessageBox.Show(messageToShow, "Error", MessageBoxButton.OK, MessageBoxImage.Error);
}

In above line of code, we show a MessageBox to user.
For this, we use MessageBox.Show method.
For more details on MessageBox.Show method please read previous section of this article.
Parameter values we used in our code are as follows:

Parameter Name	Value Used
messageBoxText	`messageToShow`
caption	`"Error"`
button	`MessageBoxButton.OK`
icon	`MessageBoxImage.Error`

Update `MainWindowViewModel` For Message Service

Open MainWindowViewModel.cs file.
Add DeleteFile property as shown below.

Please see below code for adding DeleteFile property.

private bool _DeleteFile;
public bool DeleteFile
{
    get { return _DeleteFile; }
    set { SetProperty(ref _DeleteFile, value); }
}

Show message for Empty `FilePath` property

Show error message to user if we browsed a file or not.
Please see below 👇🏻 image for how to add code for showing error message.

Please see below code for showing error message on empty browsed file.

// Check if we browsed a file
if (string.IsNullOrEmpty(FilePath))
{
    // Show information that file is deleted.
    this.eventAggregator.GetEvent<ErrorMessagesService>().Publish("Empty File Path.");
    return;
}

In above code, we check condition, if FilePath property is empty or not.
- Condition: if (string.IsNullOrEmpty(FilePath))
If FilePath property is empty, then we show error message to user.
- Error Message: Empty File Path.
We show this message by publishing ErrorMessagesService service as shown below 👇🏻.

this.eventAggregator.GetEvent<ErrorMessagesService>().Publish("Empty File Path.");

Please see below 👇🏻 image for error message.

After showing message, we exit the ExecuteClickCommand() method.
Please visit 🚀 Understand ErrorMessages method section of this article for more details.

Show message if browsed file exist or not

Show error message to user if browsed file exist or not.
Please see below 👇🏻 image for how to add code for showing error message.

Please see below code for showing error message on empty browsed file.

// Check if browsed file exist or not
if (File.Exists(FilePath) == false)
{
    // Show information that file is deleted.
    this.eventAggregator.GetEvent<ErrorMessagesService>().Publish($"[{FilePath}] did not exist.");
    return;
}

In above code, we check condition, if selected file in FilePath property exist or not.
- Condition: File.Exists(FilePath) == false
If selected file in FilePath property does not exist, then we show error message to user.
- Error Message: [{FilePath}] did not exist.
We show this message by publishing ErrorMessagesService service as shown below 👇🏻.

this.eventAggregator.GetEvent<ErrorMessagesService>().Publish($"[{FilePath}] did not exist.");

Please see below 👇🏻 image for error message.

After showing message, we exit the ExecuteClickCommand() method.
Please visit 🚀 Understand ErrorMessages method section of this article for more details.

Get Confirmation From User

Please see below code for Get confirmation from user.

// Get confirmation from user
this.eventAggregator.GetEvent<ConfirmationMessagesService>().Publish($"Do you want to delete [{FilePath}]?");

We get confirmation by publishing ConfirmationMessagesService service.
This will show a confirmation message to user and ask his confimation as shown in below 👇🏻 image.
- Confirmation Message: Do you want to delete [{FilePath}]?

Please visit 🚀 Understand ConfirmationMessages method section of this article for more details.

When User Declined Confirmation

In this section, we check, if user not give confirmation for deleting file.

// Not confirmed then clear data and exit function.
if (!DeleteFile)
{
    ClearData();
    return;
}

In code sample, we check if value of DeleteFile property is set to false.
- Condition: !DeleteFile
This if above condition is true, we call a function named ClearData() method.
Code for ClearData() method is given below.

/// <summary>
/// Method for clearing <see cref="FilePath"/> property.
/// </summary>
void ClearData() => FilePath = string.Empty;

In above code, we create an expression method.
Since there is only 1 line of statement, we create expression method.
In ClearData() method, we set the value of FilePath property to string.Empty.
By setting this value, we empty the textblock value.

When User Give Confirmation for Deleting File

// Show busy indicator
IsBusy = true;

await Task.Run(() =>
{
    // Delete Selected File
    File.Delete(FilePath);

});

// Hide busy indicator
IsBusy = false;

Above code sample is already explained in 🚀 Update MainWindowViewModel section of this article.
Please visit 🚀 Update MainWindowViewModel section of this article.

Show Success Message To User

Please see below code for Show information that file is deleted.

// Show information that file is deleted.
this.eventAggregator.GetEvent<InformationMessagesService>().Publish("File sucessfully deleted.");

We show information by publishing InformationMessagesService service.
This will show a information message to user File sucessfully deleted. as shown in below 👇🏻 image.
- Information Message: File sucessfully deleted.

-result.gif

Please visit 🚀 Understand InformationMessages method section of this article for more details.

Final Result

Now we run the application as shown in below 👇🏻 image.

-result.gif

Now we are able to delete browsed file in MVVM pattern successfully.

This is it !!!

I hope my efforts will helpful to someone!

If you found anything to add or update, please let me know on my e-mail.

Hope this post helps you to show message services to users in WPF Prism application.

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Do let me know by you like this post or not!

Till then, Happy learning!!!

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