❣️ 🎱 👇🏼 In days of doubt, in days of painful deliberation 👨🏾‍🍳 💺 🙀

In this article, I want to tell you how I visualized statistics on the ongoing pandemic, and share what features you can meet using Avalonia UI for this.

From the author

, . . — MIT .

Introduction

This article assumes that you can already create a simple application using AvaloniaUI. If not, check out the AvaloniaUI or Habr tutorials .

Data

First of all, the question arose of where to get the latest data and a quick search in Google found the following api that met all my requirements:

General information on the world
General information for each country
History for each country

Application structure

The application consists of 3 different screens.

Screenshots

The movements between the screens are built using routing . An interesting feature at this point was the transfer of the trigger for the route to UserControl.

To do this, its ViewModel had to accept Action:

 public CountriesVM(IScreen screen, Action<Country> a)

 CurrentCountyCommand = 
            CountriesCommand = ReactiveCommand.CreateFromObservable(
                () => Router.Navigate.Execute(new CountriesVM(this,GoToCurrentCountry))
                );
....
  public void GoToCurrentCountry(Country c)
        {
            CurrentCountyCommand.Execute(c);
        }

And the call to this action is to select an item in the list:

public Country SelectedCountry
        {
            get => _country;
            set
            {
                this.RaiseAndSetIfChanged(ref _country, value);
                A.Invoke(value);
            }
        }

Inquiries

For calls to api, the flurl library was used. Which internally uses HttpClient and Newtosoft, and itself is an extension for strings.

Therefore, obtaining a model from a request can be implemented in one line:

 var allCases = await "https://corona.lmao.ninja/all".GetJsonAsync<AllCases>();

Images

To work with the image using flurl, we got a stream that needed to be packed into memorystream to create a Bitmap instance:

private async Task<Bitmap> GetFlag(String flagUrl)
        {
            var flagStream = await flagUrl.GetStreamAsync();
            var memoryStream = new MemoryStream();
            flagStream.CopyTo(memoryStream);
            memoryStream.Position = 0;
            var bitmap = new Bitmap(memoryStream);
            return bitmap;
        }

Collection and Filtering

Dinamic Data from ReactiveUI was used to display the collection .

 SourceList<Country> countries = new SourceList<Country>();
 private ReadOnlyObservableCollection<Country> _collection;
 public ReadOnlyObservableCollection<Country> Collection => _collection;

countries.Connect().Filter(filter).ObserveOn(RxApp.MainThreadScheduler).Bind(out _collection).Subscribe();

I also decided to add a filter to quickly search for a country by its name or ISO3 abbreviation .

To do this, the search string was bound to the property:


        public string FilterName
        {
            get => _filterName;
            set { this.RaiseAndSetIfChanged(ref _filterName, value); }
        }

Filter rule added:

        private Func<Country, bool> Filter(string filterName)
        {
            if (string.IsNullOrEmpty(filterName)) return x => true;
            return x => x.Name.ToUpper().Contains(filterName.ToUpper()) || x.ISO3.Contains(filterName.ToUpper());
        }

And the filter itself is created:

  var filter = this.WhenValueChanged(x => x.FilterName).Select(Filter);

Graph display

For graphs, I used the Oxyplot library for AvaloniaUI.

Unfortunately, the version is outdated in nuget or I didn’t find it, so you can use the nuget package I built , or drag down the source with github.

To work, you need to add to App.xaml:

<StyleInclude Source="resm:OxyPlot.Avalonia.Themes.Default.xaml?assembly=OxyPlot.Avalonia"/>

To display an axis with a specific date, and not an arbitrary number (into which oxyplot converts the date for internal work), you must specify the type of axis in the markup:

           <avalonia:Plot.Axes>
               <avalonia:DateTimeAxis StringFormat="yyyy-MM-dd" Position="Bottom"></avalonia:DateTimeAxis>
           </avalonia:Plot.Axes>

Sources and applications

Using dotnet publish, I compiled binaries for the main platforms ( here ), and for those who will be more interested. source code can be found on github .

Instead of an afterword

This application is based on a third-party api, and I hope that soon this api will no longer be supported, because there will be no need.

Wash your pens and sit at home. And support for Avalonia can be found here .

In days of doubt, in days of painful deliberation