difference between Panel and UserControl c#

Question

有人可以告诉我使用表单、面板或用户控件之间的区别吗？

Answer 1

A form is a control and a container for other controls. A form is the base unit of a windows application.

A panel is a control and a container for other controls.

A usercontrol is a user defined control.

See:

• Windows Forms
• Windows Forms Controls
• Windows Forms Overview

In Windows Forms, a form is a visual surface on which you display information to the user. You ordinarily build Windows Forms applications by adding controls to forms and developing responses to user actions, such as mouse clicks or key presses. A control is a discrete user interface (UI) element that displays data or accepts data input.

When a user does something to your form or one of its controls, the action generates an event. Your application reacts to these events by using code, and processes the events when they occur. For more information, see Creating Event Handlers in Windows Forms.

Answer 2

According to MSDN the Panel class is "Used to group collections of controls", while the User Control "Provides an empty control that can be used to create other controls".

You are right: this doesn't help you a lot to decide whether you should use a Panel or a User Control.

One of the differences is that a Panel is a ScrollableControl, while a UserControl is a ContainerControl (which is also a ScrollableControl). So if you want ContainerControl functionality, consider to use a UserControl.

You'll probably don't know what a ContainerControl does, so what you can't do with a Panel, hence the following might be more useful:

In object oriented programming, and so also in Winforms, whenever you want a class that behaves like another class, but only slightly different, you consider to derive from the other class.

So if you want a button that changes color when pressed, and returns to its original color when pressed again, (like an on-off button), you might consider to derive from class Button, or maybe from class CheckBox-in-the-shape-of-a-button.

By making it a separate class, you can reuse the code in similar situations. Whenever you will only use it once, then usually we won't bother to make it a special class. We will usually not make a special class for "The Select button in my form, which does ... when clicked", but if you will use this button in ten different forms, then it is probably wiser to create a SelectButton class.

Similar, if you have a group of controls, with some behaviour, and you plan to use that in different forms, consider to create a User Control, where you put this behaviour. The nice thing is that the code of this behaviour is hidden in side the control. Users of your UserControl only have to know what it does, not how this is done. You might even want to hide how this is done, so users (= code, not operators) can't access it

A panel is more or less like a GroupBox without a surrounding rectangle: consider to use it instead of a User Control if you will be using it only inside this Form. Similar to how you would us a "Button that does ... when clicked": because you use it only here, you don't derive from it.

I seldom use a Panel. The derived classes: TabPage, SplitterPanel, ... are more likely to be used only in this form.

Whenever I need combinations of several controls, especially if they interact with each other, like a text box and a label that describes what is in the textbox and an OK button that processes the text in the text box, I usually make it a UserControl.

I could have derived from a Panel and add a Label, TextBox and Button, but then users could mess up with my Panel by adding other items, or calling Panel functions that would mess with my funcitonality.

Come to think of it: using a class derived from a Panel vs using a UserControl is similar to deriving vs aggregation / composition: If you aggregate, you can limit access to functionality, if you derive, users can access all parent functionality.

So if you only want limited functionality: show / no show, maybe size and position, background, but not much more: consider to create a UserControl. If you want the possibility to change the behaviour, consider to use a Panel, especially if you will use it in only one form.