updating progress bar using Task parallel library - xamarin

Question

I am trying to update the list of progress bars to show the image download progress using Task Parallel Library in Xamarin.Forms
For now I have written a block of code to simulate the download process by using a delay.
Here is my Xaml file where a ListView named MediaList resides with one caption and progress bar per item.
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="ImageTask.View.ImageTaskView">
<ContentPage.Content>
<ListView ItemsSource="{Binding MediaList}" CachingStrategy = "RecycleElement" VerticalOptions="FillAndExpand" >
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Orientation="Vertical">
<Label Text = "{Binding mediaName}" FontSize="22" />
<ProgressBar Progress="{Binding mediaProgress}"></ProgressBar>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</ContentPage.Content>
</ContentPage>
Here is my view model in which I have created one action block that takes the entire list of media object and tries to update the progress bar.
However, my main issue is I am not able to see the progress updated in my UI , so I don't know how shall I update my UI.
public class ImageTaskViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private IList<MediaInfo> _mediaList;
protected void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
public IList<MediaInfo> MediaList
{
get { return _mediaList; }
set
{
_mediaList = value;
OnPropertyChanged("MediaList");
}
}
public ImageTaskViewModel()
{
Action<IList<MediaInfo>> progressActionBlock = mediaInfoList =>
{
// infinite loop to simulate download
while (true)
{
IEnumerator<MediaInfo> dataList = mediaInfoList.GetEnumerator();
Task.Delay(2000).Wait();
while (dataList.MoveNext())
{
MediaInfo mediaInfo = dataList.Current;
Debug.WriteLine("media name " + mediaInfo.mediaName + " progress " + mediaInfo.mediaProgress);
if (mediaInfo.mediaProgress == 1)
{
Debug.WriteLine("media name " + mediaInfo.mediaName + " Done ");
break;
}
else
{
mediaInfo.mediaProgress = mediaInfo.mediaProgress + 0.1;
}
}
}
};
var opts = new ExecutionDataflowBlockOptions()
{
MaxDegreeOfParallelism = 2
};
var progressAction = new ActionBlock<IList<MediaInfo>>(progressActionBlock, opts);
MediaList = new List<MediaInfo>();
for (int i = 1; i < 6; i++)
{
MediaInfo mediaInfo = new MediaInfo();
mediaInfo.mediaName = i.ToString();
MediaList.Add(mediaInfo);
}
// Exectue Action block
progressAction.Post(MediaList);
}
}
Model of MediaInfo:
public class MediaInfo
{
public string mediaId { get; set; }
public string mediaName { get; set; }
public string mediaPath { get; set; }
public byte[] mediaStream { get; set; }
public double mediaProgress { get; set; } = 0.1;
}

Answer 1

In your View model you don't have mediaProgress. You should add
Double _mediaProgress;
public Double mediaProgress{
get{
return _mediaProgress;
} set{
_mediaProgress = value;
OnPropertyChanged("Email");
}
}
And then in your all method you use mediaProgress to set the progress.