Question

This question is the result of my previous question DataGrid – grid selection is reset when new Data is arrived

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I have such DataGrid

<DataGrid AutoGenerateColumns="True" HorizontalAlignment="Stretch" Name="dataGrid1" VerticalAlignment="Stretch" ItemsSource="{Binding DataList}" IsReadOnly="True"/>

In my ViewModel I have such field:

public ObservableCollection<ConsoleData> DataList { get; set; }

And such method which is called every second:

private void model_DataArrived(List<ConsoleData> dataList)
{
    DataList.Clear();
    dataList.ForEach(x => DataList.Add(x));
}

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We have figured out that because I call DataList.Clear the selection in the UI control is cleared as well and I don’t want this to happen. So likely I should not replace instances of ConsoleData in ViewModel, instead of that I should update these instances.

But ObservableCollection observes for add/remove I guess and doesn’t observe for update isn’t? So if I will update instances DataBinding will not work?

Another problem with the current application is that dataList.ForEach(x => DataList.Add(x)); forces databinding to execute on each iteration instead of executing only at the end?

Overall what is the right way to do what I want to do because current application doesn’t work and has too many problems…

Answer 1

It’s not clear how you are planning on updating an item in your ObservableCollection. There are at least two ways to do this. One way is to update all the properties that are changed in a ConsoleData object. In this case, you would have ConsoleData implement INotifyPropertyChanged. Another way is a direct update of item in the ObservableCollection. To do this, you could use the SetItem method of the ObservableCollection. This will raise the CollectionChanged event as the MSDN documentation for SetItem indicates.

Since you have indicated that you are using MVVM, the generally accepted thing to do would be to make your ObservableCollection be a collection of ConsoleDataViewModel instead of ConsoleData.

Another problem with the current application is that dataList.ForEach(x => DataList.Add(x)); forces databinding to execute on each iteration instead of executing only at the end?

I don’t think you will have the refresh problem if you modify your model_DataArrived method to update instead of clear/add as indicated above.