Understanding the SetStyle Method

2017-11-03 09:05:09

Windows Forms and controls provide built-in support for double buffering, and the SetStyle method of the Control class plays a vital role in this process. Before we discuss how to use SetStyle, let's take a look at this method and its members.

The SetStyle method is defined in System.Windows.Forms.Control, which sets the specified style of a control. This method takes two arguments. The first argument is of type ControlStyle enumeration, and it represents the style of the control. The second argument is true if we want to apply the specified style, false otherwise. The members of the ControlStyle enumeration are described in Table 13.1.

Table 13.1. `ControlStyle` members
Member	Description
`AllPaintingInWmPaint`	The `WM_ERASEBKGND` window message is sent to the message queue whenever a control needs to redraw its background. This method tells Windows to ignore the message, reducing flicker. Both `OnPaint` and `OnPaintBackground` are called from the window message `WM_PAINT.AllPaintingInWmPaint` should be used only if `UserPaint` is set to `true`.
`CacheText`	Applications can cache text using this option. The control keeps a copy of the text rather than getting it from the handle each time it is needed. This style defaults to `false`.
`ContainerControl`	The control is a container.
`DoubleBuffer`	This method provides built-in support for double buffering. When it is set to `true`, drawing is performed in a buffer and displayed only when complete. When using this option, you must also set the `UserPaint` and `AllPaintingInWmPaint` bits to `true`.
`EnableNotifyMessage`	If `true`, the `OnNotifyMessage` method is called for every message sent to the control's `WndProc` method. This style defaults to `false`.
`FixedHeight`	The control has a fixed height.
`FixedWidth`	The control has a fixed width.
`Opaque`	The control is drawn opaque, and the background is not painted.
`ResizeRedraw`	The control is redrawn when it is resized.
`Selectable`	The control can receive focus.
`StandardClick`	The control implements standard click behavior.
`StandardDoubleClick`	The control implements standard double-click behavior. When using this option, you must also set `StandardClick` to `true`.
`SupportsTransparentBackColor`	The control accepts a `Color` object with alpha transparency for the background color. The `UserPaint` bit must be set to `true`, and the control must be derived from the `Control` class, like this: `this.SetStyle(ControlStyles.UserPaint, true);`
`UserMouse`	The control does its own mouse processing, and mouse events are not handled by the operating system.
`UserPaint`	The control paints itself rather than having the operating system do it. This option applies to classes derived from `Control`.

Let's apply the SetStyle method to achieve double buffering. Double buffering can be enabled programmatically with the following code:

// Activates double buffering this.SetStyle(ControlStyles.UserPaint, true); this.SetStyle(ControlStyles.AllPaintingInWmPaint, true); this.SetStyle(ControlStyles.DoubleBuffer, true);

We can also control the redrawing of controls when a control is resized. Setting ControlStyle.ResizeRedraw to true, as in the code snippet that follows, forces controls to be redrawn every time a control (or a form) is resized.

SetStyle(ControlStyles.ResizeRedraw, true);

Sometimes we will not want a control to be redrawn when it is resized. In this case we can set ResizeRedraw to false.

Note

Many controls, such as PictureBox, are double-buffered automatically, which means we don't need to write any additional code when viewing images in a PictureBox control.

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