MainWindow.xaml.cs里加入

// 设置全屏
this.WindowState = System.Windows.WindowState.Normal;
this.WindowStyle = System.Windows.WindowStyle.None;
this.ResizeMode = System.Windows.ResizeMode.NoResize;
this.Topmost = true;
this.Left = 0.0;
this.Top = 0.0;
this.Width = System.Windows.SystemParameters.PrimaryScreenWidth;
this.Height = System.Windows.SystemParameters.PrimaryScreenHeight;