How do I print just one or two controls instead of the whole form in Visual Basic_问答_开发者

I have a program that gives the user driving directions, I would like the user to be able to print just the directions or just the directions and a map by selecting a corresponding radio button for each option. How can I print just these sections and not the whole form? And how can I use the radio buttons to tell it what to print? Thanks

Updated code:

Private Sub btnprint_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnprint.Click
        If rbprintall.Checked = True Then
            'Ad code to print all here
        ElseIf rbprintdirections.Checked = True Then
            lbldirections.DrawToBitmap()
            lbldirections2.DrawToBitmap()
            lbldirections3.DrawToBitmap()
            lbldirections4.DrawToBitmap()

        Else
            MessageBox.Show("You must select one of the开发者_C百科 above options!")
        End If

If you're using Windows Forms, almost all of the built-in controls can be easily rendered to an image using their DrawToBitmap method. If you simply want to print whatever is currently displayed by a control, this is the easiest way to do it. Do note, however, that there are a couple of caveats to what can be drawn this way. See the linked documentation for details.

Printing in the .NET Framework is also made relatively simple by taking advantage of the functionality provided in the System.Drawing.Printing namespace. If you aren't already experienced with this, Google for some tutorials. For example, there's a pretty good article here from the MSDN Magazine.

So, to accomplish your ultimate goal, you'll need to do the following:

When the user clicks "Print", determine which radio button is currently selected.
Create a temporary bitmap and grab a copy of the appropriate control in that bitmap using the control's DrawToBitmap method. (If you need to print multiple controls, create a separate temporary bitmap for each of them, and then print each of them in the next step.)
Draw that image to the printer using the Graphics.DrawImage method in the PrintPage event handler method for a PrintDocument object you've created.

EDIT: I'm not really sure where your question is with regards to the code that you've posted, but I see two primary problems.

In the first block of your if statement, the comment suggests you don't know how to print all of the controls. You have a couple of different options. If you just want to print every control on the form as it appears, you can simply use the DrawToBitmap method of the Form itself. That will create a bitmap of the form's entire client area, including all of the controls it contains.

If there are still some controls on the form that you don't want to print, even when the user chooses "Print All", you'll need to call the DrawToBitmap methods on each individual control. You might set up a loop so that you don't have to write a line of code for every control, but there's not really another good option.
I suspect you're going to have problems with the second elseif block working as you expect it to, also. Recall that I said above you need to create temporary bitmap images, and then draw into those bitmaps? The DrawToBitmap method takes two parameters:
- bitmap: a System.Drawing.Bitmap that you want an image of the control to be drawn into
- targetBounds: a System.Drawing.Rectangle that describes the bounds of the control that will be rendered
The code you've shown is missing both of those parameters. In this case, the second (targetBounds) is simple—because you want to draw the entire control, all you need to do is specify it's ClientRectangle property for that parameter.

For the first (bitmap) parameter, you need to do as I mentioned above and create a new Bitmap image by declaring a temporary variable. Then, you need to call the DrawToBitmap method with this temporary bitmap specified.

Maybe I can be clearer with an example. Modify your above code to look like this:
```
'Declare some class-level variables to hold images of the controls to print
Private bmpDirections1 As System.Drawing.Bitmap
Private bmpDirections2 As System.Drawing.Bitmap
Private bmpDirections3 As System.Drawing.Bitmap
Private bmpDirections4 As System.Drawing.Bitmap

Private Sub btnprint_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnprint.Click
   If rbprintall.Checked = True Then
      'Add code to print all here
   ElseIf rbprintdirections.Checked = True Then
      'Draw lbldirections control to bitmap variable named bmpDirections1
      bmpDirections1 = New Bitmap(lbldirections.Width, lbldirections.Height)
      lbldirections.DrawToBitmap(bmpDirections1, lbldirections.ClientRectangle)

      'Draw lbldirections2 control to bitmap variable named bmpDirections2
      bmpDirections2 = New Bitmap(lbldirections2.Width, lbldirections2.Height)
      lbldirections2.DrawToBitmap(bmpDirections2, lbldirections2.ClientRectangle)

      'Draw lbldirections3 control to bitmap variable named bmpDirections3
      bmpDirections3 = New Bitmap(lbldirections3.Width, lbldirections3.Height)
      lbldirections3.DrawToBitmap(bmpDirections3, lbldirections3.ClientRectangle)            

      'Draw lbldirections4 control to bitmap variable named bmpDirections4
      bmpDirections4 = New Bitmap(lbldirections4.Width, lbldirections4.Height)
      lbldirections4.DrawToBitmap(bmpDirections4, lbldirections4.ClientRectangle) 
   Else
      MessageBox.Show("You must select one of the above options!")
   End If
End Sub
```
The only thing to remember is that you need to call the Dispose method on each bitmap variable when you are finished using it. The Dispose method "releases the resources owned by the image", which means that it frees up the memory it was using. There's no reason to keep those large-ish images around if you're not going to use them again. So, you should probably do this after the print job is completed. Once you dispose the bitmap object, you will no longer be able to use the image it contained, but you can always create a new bitmap object and assign it to the variable (as shown in the above code) the next time the user clicks print.
Unrelated: There's no reason to test for If x = True. The simpler If x is the same thing, and considered by most programmers to be better style. Effectively, you're doing a double comparison against True, which isn't necessary.