Better error handling for Mac demo

Emgu.CV.Example/Mac/Emgu.CV.Example.Mac.csproj

@@ -151,9 +151,11 @@
   <ItemGroup>
     <Content Include="..\..\opencv\data\haarcascades\haarcascade_eye.xml">
       <Link>haarcascade_eye.xml</Link>
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
     <Content Include="..\..\opencv\data\haarcascades\haarcascade_frontalface_default.xml">
       <Link>haarcascade_frontalface_default.xml</Link>
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
     <Content Include="..\FaceDetection\lena.jpg">
       <Link>lena.jpg</Link>

Emgu.CV.Example/Mac/ViewController.cs

@@ -56,6 +56,8 @@ namespace Emgu.CV.Example.Mac
 		}
 
 		void RunDetectFace()
+		{
+            try
             {
                 //Read the files as an 8-bit Bgr image  
                 NSImage nsImage = NSImage.ImageNamed("lena.jpg");
@@ -77,6 +79,14 @@ namespace Emgu.CV.Example.Mac
                     CvInvoke.Rectangle(image, eye, new Bgr(Color.Blue).MCvScalar, 2);
 
                 mainImageView.Image = image.ToNSImage();
+            } catch (Exception e)
+            {
+                InvokeOnMainThread(() =>
+                {
+                    messageLabel.StringValue = e.Message;
+                    messageLabel.InvalidateIntrinsicContentSize();
+                });
+            }
 		}
 
 		void RunFeatureMatching()
@@ -119,7 +129,7 @@ namespace Emgu.CV.Example.Mac
 
 		private void ProcessFrame(object sender, EventArgs arg)
 		{
-			if (_capture != null && _capture.Ptr != IntPtr.Zero)
+			if (_capture != null && _capture.Ptr != IntPtr.Zero && _capture.IsOpened)
 			{
 				_capture.Retrieve(_frame, 0);
 				var nsImage = _frame.ToNSImage();
@@ -137,11 +147,11 @@ namespace Emgu.CV.Example.Mac
 				_capture = new VideoCapture();
 				if (_capture == null || !_capture.IsOpened)
 				{
+                    _capture = null;
                     InvokeOnMainThread(() =>
 					{
 						messageLabel.StringValue = "unable to create capture";
 					});
-					_capture = null;
 					return;
 				}
 				_capture.ImageGrabbed += ProcessFrame;