Open new progressbar window in WPF with MVVM pattern.

In your ViewModel you need to set up the BackgroundWorker so that it reports progress back to the UI thread from the threadpool thread that runs your DoWork method.

public   class ViewModel : INotifyPropertyChanged
    {
        private BackgroundWorker worker;
        private bool isLoading=false;

  public ViewModel()
        {
            worker = new BackgroundWorker();
            worker.WorkerReportsProgress = true;
            worker.ProgressChanged += (sender, args) =>
            {
                int visibilitySetting = args.ProgressPercentage;
                IsLoading = visibilitySetting == 0 ? false : true;
             };
            worker.DoWork += WorkerDoWork;
        }
        public bool IsLoading
        {
            get
            {
                return isLoading;
            }
            set
            {
                isLoading = value;
                OnPropertyChanged();
            }
        }
        private ICommand loadCommand;
        public ICommand LoadCommand
        {
            get
            {
                return loadCommand ?? (loadCommand = new DelegateCommand(Load));
            }
        }

        public void Load()
        {
           worker.RunWorkerAsync();
        }


        private void WorkerDoWork(object sender, DoWorkEventArgs e)
        {
            worker.ReportProgress(1);//shows progress bar
            Thread.Sleep(1500);     //load data
            worker.ReportProgress(0);//hides progress bar
        }

In the Xaml, place the ProgressBar inside a fixed-sized Grid so that the layout is not corrupted when the visibility changes. Bind the Visibility property to the view model’s IsLoaded property. Use the BooleanToVisibilityConverter to enable it to bind to IsLoaded. Something like this.

<Window x:Class="WpfProgress.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfProgress"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Window.Resources>
        <BooleanToVisibilityConverter x:Key="boolToVisibilityConverter" />
    </Window.Resources>
    <Window.DataContext>
        <local:ViewModel />
    </Window.DataContext>
    <Grid  Background="white" Height="400" >
 
        <StackPanel>
        <TextBlock  Text="uploading...."  />
        <Grid Height="30">
        <ProgressBar x:Name="ProgressUpload"    IsIndeterminate="True" Height="30"  Width="328" VerticalContentAlignment="Center"  
                        Visibility="{Binding Path=IsLoading, Converter={StaticResource boolToVisibilityConverter}}"/>
        </Grid>
        <Button x:Name="button"   Content="Cancel Upload " Height="31" Width="127" Margin="10,25,0,0" Command="{Binding hello}" />
            <Button  Content="Upload "   Height="31" Width="127" Margin=" 10,25,0,0" Command="{Binding LoadCommand}" />
        </StackPanel>
    </Grid>
</Window>