在C＃中布置字体对象

Question

I have the following code

Font font = ComboBox.Font;
if(condition1)
font = new Font(font, FontStyle.Bold);
if(condition2)
  e.Graphics.DrawString("One", font, color, rectangle);
else
  e.Graphics.DrawString("Two", font, color, rectangle);
font.Dispose();

When I run the code analysis, it shows an error that 'font' is not disposed along all exception paths. What's the proper way to dispose it in the above code?

Thanks.

Answer 1

You should not Dispose ComboBox.Font : it should do ComboBox itself . You can create a Font copy instead:

using (Font font = new Font(ComboBox.Font, condition1 ? FontStyle.Bold : ComboBox.Font.Style)) {
  if (condition2)
    e.Graphics.DrawString("One", font, color, rectangle);
  else
    e.Graphics.DrawString("Two", font, color, rectangle);
}

Answer 2

The clue is in the phrase "all exception paths". Essentially, Code analysis has noticed that an exception could be thrown by the DrawString calls, and that the Dispose would not be called in that case.

There is also the question of disposing an object which you did not create, so a simple flag would suffice there.

As Samuel noted in the comments, wrap the block in a try...finally and call Dispose in the finally block, like this:

Font font = ComboBox.Font;
bool created = false;

try
{
    if(condition1)
    {
        font = new Font(font, FontStyle.Bold);
        created = true;
    }
    if(condition2)
        e.Graphics.DrawString("One", font, color, rectangle);
    else
        e.Graphics.DrawString("Two", font, color, rectangle);
}
finally
{
    if (created)
        font.Dispose();
}

Code Analysis will still complain at this, as the Dispose is conditional on the value of created , and the code analysis tool is not sophisticated enough to be able to determine that the creation and disposal conditions are identical. The solution to that is shown in Dmitry's answer , specifically to create a new Font whatever the value of condition1 , and to use that condition instead to choose the appropriate value within the font object.

Answer 3

You problem is to only dispose the font if you have to create a new one. So this is the code you need to use:

Action<Font> drawString =
    f => e.Graphics.DrawString(condition2 ? "One" : "Two", f, color, rectangle);

if (condition1)
    drawString(ComboBox.Font);
else
    using (var font = new Font(ComboBox.Font, FontStyle.Bold))
    {
        drawString(font);
    }