Casting classes up and down.
B b = new B();
A a = (A)b;
B c = a as B;
if (c != null)
{
//cast succeeded
}
>/pre>
Casting
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Category Archives: C#
Get the MyVideos folder
For the current user
System.Environment.GetFolderPath(Environment.SpecialFolder.MyVideos));
For all users
System.Environment.GetFolderPath(Environment.SpecialFolder.CommonVideos));
.NET and painting from an API viewpoint
When .NET is used on the windows platform it’s a layer on top of the windows API. Understanding how this works will help you to speed up painting.
The windows API works with messages. These message are processed by the message queue. Often the message handler is one function with a long switch statement processing the messages required.
Messages related to painting
Messages of importance are the WM_ERASEBKGND and the WM_PAINT.
WM_ERASEBKGND clears the background and paint it. It is called when a part of the control needs to be repainted. The default handling uses the brush assigned to the background and paints. When an API InvalidateRect is used to invalidate a rectangle the last parameter indicates whether this message is generated.
WM_PAINT paints the contents, it uses a clipping rectangle. The GDI API can clip all contents on this rectangle. Although clipping is not totally free it reduces the time to repaint significantly.
How does this translate to .NET.
.NET supports two events which map directly to the events.
OnPaintBackground
Called from the WM_ERASEBKGND event unless double buffering or SetStyle is used to set the style AllPaintingInWmPaint. In that case this event will be fired from the WM_PAINT message, this may reducing some flicker since there can be some time between the two messages. It is to be assumed that setting the form property DoubleBuffered to true will also set this style implicit .
Paint
Used to paint the contents. It uses a clipping rectangle to prevent unneeded painting. It is important to remember that if you invalidate the form yourself using the Invalidate() method (equivalent to an InvalidateRect API call) using the parameter less version will invalidate the entire client area!
When using invalidate always supply an rectangle or region if needed. Multiple invalidates will be combined in one clipping rectangle. Typically the bounding rectangle.
It is also important to remember that invalidate() will not repaint directly, use the update method to redraw (the equivalent of the UpdateWindow() API call.
Double buffering
When double buffering is used the graphics drawn is first drawn on a bitmap which is then drawn on screen. Although theoretically this would be slower requiring an extra step, drawing on the bitmap (in memory) is often faster then to video memory the net result may be faster. Since there will be less flicker since the screen buffer is accessed less often and bitmap drawing is a very efficient graphics operation double buffering is almost always a good idea .
It is still very important to use the Invalidate with rectangles even when double buffering. Admittedly, drawing the entire bitmap is fast but when dragging a lot of bitmaps need to be painted! Also if possible do not rely on clipping to much. Your paint handler has a parameter with the clipping rectangle. If a lot of objects are to be painted a quick check on this boundary can save precious time creating brushes, pens etc.
Remove or insert items in an ‘fixed’ array like int[]
Remove or insert an item in an array.
Use the always useful Array class. It has some static members which are great!
int[] myArray = new int[4]; myArray [0] = 0; myArray [1] = 1; myArray [2] = 2; myArray [3] = 3; // Remove item 1 Array.Copy(myArray , 2, myArray , 1, 2); // MyArray contains 0,2,3,3 myArray [0] = 0; myArray [1] = 1; myArray [2] = 2; myArray [3] = 3; // Insert new item in 1 Array.Copy(myArray , 1, myArray ,2, 2); // MyArray contains 0,1,1,2
Note: If the bounds of the array are exceeded an exception will be thrown.
The functions below calculate the number of elements to copy.
They use the following arguments:
| Array | The array to use. |
| index | The offset whereto insert or remove |
| delta | The number of items to add / remove |
| totCount | The number of items currently in the array. |
To allow a correct insert the array must be larger than the current numbers (Arrays are not resized). Clearing is optional
void removeFromArray(Array array, int index, int delta, int totCount)
{
Array.Copy(array, index + delta, array, index, totCount - (index + delta));
Array.Clear(array, totCount - delta, delta);
}
void insertIntoArray(Array array, int index, int delta, int totCount)
{
Array.Copy(array, index, array, index + delta, totCount - index);
Array.Clear(array, index, delta);
}
The Paint event only shows a large red boxed cross
In case your paint event only shows the image below, an exception is thrown inside the paint event
Adding throw(new Exception()) to the paint event will give the same result.
OutputDebugString replacement
To replace OutputDebugString API use the System.Diagnostics.Debug class.
For example:
System.Diagnostics.Debug.WriteLine("Debug message");
Full row selection for datagridview rows
Use the designer or following code:
DatagridView.SelectionMode = DataGridViewSelectionMode.FullRowSelect;
Get the send to folder
For the current user
System.Environment.GetFolderPath(Environment.SpecialFolder.SendTo));
For the all users
System.Environment.GetFolderPath(Environment.SpecialFolder.CommonSendTo));
Get the desktop folder
For the current user
System.Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory));
For the all users
System.Environment.GetFolderPath(Environment.SpecialFolder.CommonDesktopDirectory));
Get the template folder
For the current user
System.Environment.GetFolderPath(Environment.SpecialFolder.Templates));
For the all users
System.Environment.GetFolderPath(Environment.SpecialFolder.CommonTemplates));