将类型转换为System.Drawing.Image

Question

I'm having a conversion error I would like some help in overcoming.

At the moment I am trying to take a screen capture of my desktop and store it in a variable I can pass around. Right now, this code looks like this:

ScreenCapture capture = new ScreenCapture();
Image capturedImageObj=  capture.CaptureImage(showCursor, curSize, curPosition, startPoint, Point.Empty, bounds, _screenPath, fi);

However, by doing that I get the following error:

Cannot implicitly convert type 'void' to 'System.Drawing.Image'

So, I tried to type cast the capture.CaptureImage and it generated the same error. The line I wrote was thus:

Image capturedImageObj=  (Image)capture.CaptureImage(showCursor, curSize, curPosition, startPoint, Point.Empty, bounds, _screenPath, fi);

My CaptureImage method is the following:

  public void CaptureImage(bool showCursor, Size curSize, Point curPos, Point SourcePoint, Point DestinationPoint, Rectangle SelectionRectangle, string FilePath, string extension)
    {
        Bitmap bitmap = new Bitmap(SelectionRectangle.Width, SelectionRectangle.Height);

        using (Graphics g = Graphics.FromImage(bitmap))
        {
            g.CopyFromScreen(SourcePoint, DestinationPoint, SelectionRectangle.Size);

            if (showCursor)
            {
                Rectangle cursorBounds = new Rectangle(curPos, curSize);
                Cursors.Default.Draw(g, cursorBounds);
            }
        }

        if (saveToClipboard)
        {
            Image img = (Image)bitmap;

            if (OnUpdateStatus == null) return;

            ProgressEventArgs args = new ProgressEventArgs(img);
            OnUpdateStatus(this, args);

        }

So, seeing that I have set the method to be void, I changed it so that it would require an image like so:

  public Image CaptureImage(bool showCursor, Size curSize, Point curPos, Point SourcePoint, Point DestinationPoint, Rectangle SelectionRectangle, string FilePath, string extension)

But then it generated the following error:

An object of a type convertible to 'System.Drawing.Image' is required.

This error points to the following chunk of code with the second if statement being the culprit:

  if (saveToClipboard)
  {
     Image img = (Image)bitmap;

     if (OnUpdateStatus == null) return;

     ProgressEventArgs args = new ProgressEventArgs(img);
     OnUpdateStatus(this, args);
 }

I've ran out of ideas on how to beat these errors. Can anyone please shed some light / new insight so that I can get rid of them?

Answer 1

Your CaptureImage requires an Image returned but you return void/nothing in the if (OnUpdateStatus == null) . Even you return some image there, you still have to return the image outside that if block, otherwise it may complain that Not all code paths return a value .

 public Image CaptureImage(bool showCursor, Size curSize, Point curPos, Point SourcePoint, Point DestinationPoint, Rectangle SelectionRectangle, string FilePath, string extension)
{
    Bitmap bitmap = new Bitmap(SelectionRectangle.Width, SelectionRectangle.Height);

    using (Graphics g = Graphics.FromImage(bitmap))
    {
        g.CopyFromScreen(SourcePoint, DestinationPoint, SelectionRectangle.Size);

        if (showCursor)
        {
            Rectangle cursorBounds = new Rectangle(curPos, curSize);
            Cursors.Default.Draw(g, cursorBounds);
        }
    }

    if (saveToClipboard)
    {
        Image img = (Image)bitmap;

        if (OnUpdateStatus == null) return bitmap;//<--- here

        ProgressEventArgs args = new ProgressEventArgs(img);
        OnUpdateStatus(this, args);

    }
    return bitmap;//<--- and here
 }

Answer 2

because your method

public Image CaptureImage( 

expects a return type of image that you are not returning. There are 2 points of return in your code.

Point 1:

if (OnUpdateStatus == null) return;

gives error because as your return type needs to be image and you are not returning that so you should do it like

if (OnUpdateStatus == null) 
     return null; //or a valid image

and before exiting the method you need to return image as well

return someImage; //as the last line in your method before closing brackets

Answer 3

You need to actually return an Image from your CaptureImage method. Your return statement isn't returning anything.