How can I refresh the UI in MVVM WPF

Question

My project is based on the MVVM pattern.

I have built a tree view that shows my file system. Each folder has a checkbox for selecting the current folder. The selection process is taking some time so, while the operation runs, there is a button which is disabled and at the end of the operation I`m enabling the button.

My problem is that when the button gets "disabled" I see it immediately. However, when the button is going back to the enabled mode I must do some action (like mouse click) to see the button enabled.

How can I make sure that the UI will be updated immediately after the button is enabled?

These are my buttons:

<Button Content="&lt;- Back" Margin="5,0,5,0" Width="80" Height="25"
        IsEnabled="{Binding CanMoveToPreviousPage, UpdateSourceTrigger=PropertyChanged}" 
        Command="{Binding Path=NavigateBackCommand, IsAsync=True}" />

<Button Content="{Binding ButtonNextCaption}" Margin="5,0,5,0" Width="80" Height="25"
        IsEnabled="{Binding CanMoveToNextPage, UpdateSourceTrigger=PropertyChanged}" 
        Command="{Binding Path=NavigateNextCommand, IsAsync=True}" />

In my ViewModel I added this code:

public bool CanMoveToNextPage
{
    get
    {
        return this.CurrentPage != null && this.CurrentPage.CanMoveNext;
    }
    set
    {
        if (CurrentPage != null)
        {
            this.CurrentPage.CanMoveNext = value;
            OnPropertyChanged("CanMoveToNextPage");
        }
    }
}

public bool CanMoveToPreviousPage
{
    get { return 0 < this.CurrentPageIndex && CurrentPage.CanMoveBack; }
    set
    {
        if (CurrentPage != null)
        {
            this.CurrentPage.CanMoveBack = value;
            OnPropertyChanged("CanMoveToPreviousPage");
        }
    }
}

The UI update happens just after I execute a mouse click or any keystroke.

This is the code of the action that is disabling and enabling the buttons:

void bg_RunWorkerCompleted(object sender, System.ComponentModel.RunWorkerCompletedEventArgs e)
{
    DecrementDoneCounter();
    if (ThreadSafeCouner == 0)//means all bg workers are done
    {
        UIlimitation(true);
    }
}

private int ThreadSafeCouner; // check how many bgworkers run
public void IncrementDoneCounter() { Interlocked.Increment(ref ThreadSafeCouner); }
public void DecrementDoneCounter() { Interlocked.Decrement(ref ThreadSafeCouner); }


void bg_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
{
    IncrementDoneCounter();
    UIlimitation(false);
    ((bgArguments)e.Argument).SelectedDirectory.CanSelected = false;
    MarkItems(((bgArguments)e.Argument).SelectedDirectory, ((bgArguments)e.Argument).IsSelect);
    ((bgArguments)e.Argument).FreeWorkerAllocation();
    ((bgArguments)e.Argument).SelectedDirectory.CanSelected = true;
}

//this is the enabling action which execute the propeties setters at the upper part of this post
private static void UIlimitation(bool limit)
{
    MainWindowViewModel.Instance.CanMoveToNextPage = limit;
    MainWindowViewModel.Instance.CanMoveToPreviousPage = limit;
}

What can I do?

Answer 1

You can adjust on your control Binding mode TwoWay and define triggers with PropertyChanged

{Binding ElementName=.., Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}

Answer 2

OK I found a solution.
I tried everything without success and eventually I found this thread: Refresh WPF Command

I have used CommandManager.InvalidateRequerySuggested()

And its works.

Thanks for your help