Windows Forms programming in C # Reading Notes-Chapter 4 Drawing Basics

1. Drawing to the screen

Bool drawellipse = false;


Void drawellipsebutton_click (Object sender, eventargs e ){

Drawellipse =! Drawellipse;


Graphics G = This. creategraphics ();

Try {

If (drawellipse ){

// Draw the ellipse

G. fillellipse (brushes. darkblue, this. clientrectangle );

}

Else {

// Erase the previusly drawn Ellipse

G. fillellipse (systembrushes. Control, this. clientrectangle );

}

}

Finally {

G. Dispose ();

}

}

Note: The reason for adding a try-Catch Block is: "The graphic class's implementation of idisposable dispose can release the underlying graphics object that it's maintaining. the graphics object must be released. Here, you can also use the C # unique using block (dispose is automatically called after completion ):
Void drawellipsebutton_click (Object sender, eventargs e ){

Using (Graphics G = This. creategraphics ()){

If (drawellipse)

G. fillellipse (brushes. darkblue, this. clientrectangle );

Else

G. fillellipse (systembrushes. Control, this. clientrectangle );

} // G. Dispose called automatically here

}

Note: If you want to enable automatic re-painting of an ellipse during window resize. This must be added to the constructor of the Form class. setstyle (controlstyles. resizeredraw, true); add this to the button click event. refresh (); (equivalent to this. invalidate (true) plus this. update ();) but it is inefficient to automatically redraw all windows during resize, which is time-consuming.

2. Saving and restoring graphics settings

Use the graphicsstate object in system. Drawing. drawing2d namespace, and add the SAVE () and restore () Methods of the graphics class.
Void drawsomething (Graphics g ){

// Save the old

Graphicsstate oldstate = G. Save ();


// Change the smooth Mode

G. smoothingmode = smoothingmode. antialias;


// Start painting

// Restore the old

G. Restore (oldstate );

}