Peter Duniho said:
.NET != GDI+ (in spite of the close relationship between the two)
I know. I`m using both.
Also, without specifics about those examples, it's not clear that you are
comparing apples to apples even ignoring the API difference. In
particular, the Graphics instance obtained from the PaintEventArgs is
special, having been retrieved earlier on your behalf, and being disposed
later also on your behalf.
Well this is an example from the book -
Listing 2.2 Using Dispose calls
protected override void OnPaint(PaintEventArgs e)
{
// Obtain the Graphics object
Graphics g = e.Graphics;
// Set the composite quality and smoothing mode
// of the surface
g.SmoothingMode = SmoothingMode.AntiAlias;
// Create a rectangle from point (20, 20) to (100, 100)
Rectangle rect = new Rectangle(20, 20, 100, 100);
// Create two Pen objects, one red and one black
Pen redPen = new Pen(Color.Red, 3);
Pen blackPen = Pens.Black;
// Create a SolidBrush object
SolidBrush greenBrush = new SolidBrush(Color.Green);
// Draw shapes and lines
g.DrawRectangle(redPen, rect);
g.FillEllipse(greenBrush, rect);
g.DrawLine(blackPen, 0, 250, this.Width, 250);
g.FillEllipse(Brushes.Blue, 70, 220, 30, 30);
g.FillEllipse(Brushes.SkyBlue, 100, 210, 40, 40);
g.FillEllipse(Brushes.Green, 140, 200, 50, 50);
g.FillEllipse(Brushes.Yellow, 190, 190, 60, 60);
g.FillEllipse(Brushes.Violet, 250, 180, 70, 70);
g.FillEllipse(Brushes.Red, 320, 170, 80, 80);
// Dispose of objects
greenBrush.Dispose();
// blackPen.Dispose();
redPen.Dispose();
g.Dispose();
}
It is definitely not true that you only need to call Dispose() on objects
your own code has specifically created using "new". But in this
particular case, you are correct that that particular Graphics instance is
not your responsibility to dispose.
The reason I was surprised at the Dispose above is when I was learning a bit
about
classes and subclassing I created a custom label as an excercise. All I did
was
give options for the text in the label to have a shadow or a border.
However, if
i use g.Dispose() at the end of the paint event the app will crash
protected override void OnPaint(PaintEventArgs e)
{
if (this.__prvCustomFontStyle == CustomFontStyle.None)
{
base.OnPaint(e);
return;
}
Graphics g = e.Graphics;
g.TextRenderingHint = TextRenderingHint.AntiAlias;
this.drawSize = e.Graphics.MeasureString(this.Text, this.Font,
new PointF(), StringFormat.GenericTypographic);
< Text Alignment stuff snipped for brevity>
if (__prvCustomFontStyle == CustomFontStyle.Outline)
{
float fontSize = e.Graphics.DpiY * this.Font.SizeInPoints /
72;
this.drawPath.Reset();
this.drawPath.AddString(this.Text, this.Font.FontFamily,
(int)this.Font.Style, fontSize, point, StringFormat.GenericTypographic);
g.FillPath(this.foreColorBrush, this.drawPath);
g.DrawPath(this.textBorderPen, this.drawPath);
}
else //Shadow
{
g.DrawString(this.Text, this.Font, new
SolidBrush(this.ShadowColor), this.Displacement.X + point.X,
this.Displacement.Y + point.Y);
g.DrawString(this.Text, this.Font, new
SolidBrush(this.ForeColor), point);
}
// g.Dispose(); //BOOOM!
}
mick
