Windows form is going to bakground, after alt+tabbing it is appearing on top of the display

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WPF

WinForms

My application is combination of WPF and Winforms.
Displaying a windows form in the thread process without blocking the code, but the form is going to the background.
In the Form handle event the handle value is zero.

Form should be display on the top of the WPF Window.

public partial class MainWindow : Window
    {
     public MainWindow()
     {    
       InitializeComponent();            
       Thread processPostScanThread = new Thread(() => ProcessThreadScannedFile("test"));
       processPostScanThread.SetApartmentState(ApartmentState.STA);            
       processPostScanThread.Start();           
     }
     private object ProcessThreadScannedFile(string p1)
     {
       win_form sc = new win_form ();   
       Task.Run(() => sc.ShowDialog());  
       return true;
     }
   }

Note:
MainWindow = WPF window
win_form = Windows form

What I have tried:

Quote:

I have tried using pinvoke methods like (FindWindowA,SetForeGroundWindow etc.,)

this.Focus();
this.Activate();
this.BringFront();

above all the three lines executed in shown,handle, activated event but also it also going in background.