Form constructor vs Form_Load

c# winforms constructor onload
Ryan picture Ryan · Apr 12, 2010 · Viewed 26.4k times · Source

Whats the difference between a form constructor and the form_Load method?

Whats your though process for placing items in one vs the other?

Answer

Hans Passant picture Hans Passant · Apr 12, 2010

Don't use the Load event, override the OnLoad() method. That ensures that everything runs in a predictable order when you derive from the form class. You should only use it for form initialization that requires the size of the actual form to be know. It can be different from the design size due to scaling or user preferences and the actual size isn't know until the native window is created.

Initializing controls in the OnLoad method is possible but it can be very slow, especially for ListView and TreeView. If you initialize them in the constructor, they can be bulk-initialized when their native Windows controls are created.

One special exception: creating an MDI child window should always be done in OnLoad(), there's a bug in the plumbing code that messes up the MDI bar when you create a child in the constructor.

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