Button. Command Событие

Определение

Возникает при щелчке элемента управления Button. Occurs when the Button control is clicked.

Тип события

Реализации

Примеры

В следующем примере кода показано, как задать и закодировать обработчик события для Command сортировки списка при Button щелчке элемента управления. The following code example demonstrates how to specify and code an event handler for the Command event to sort a list when the Button control is clicked. В этом примере обработчик событий задается декларативно с помощью OnClick свойства Button элемента управления. This example specifies the event handler declaratively, using the OnClick property of the Button control.

В следующем примере кода показано, как задать обработчик событий и программным образом добавить его в событие в Page_Load методе. The following code example demonstrates how to specify the event handler and programmatically add it to the event in the Page_Load method.

Комментарии

CommandСобытие возникает при Button щелчке элемента управления. The Command event is raised when the Button control is clicked. Это событие часто используется, когда имя команды, например Sort , связано с Button элементом управления. This event is commonly used when a command name, such as Sort , is associated with the Button control. Это позволяет создавать несколько Button элементов управления на веб-странице и программно определять, какой Button элемент управления щелкнул. This allows you to create multiple Button controls on a Web page and programmatically determine which Button control is clicked.

CommandСобытие вызывается через иерархию элементов управления в форме BubbleEvent . The Command event is raised through the control hierarchy in the form of the BubbleEvent .

Дополнительные сведения об обработке событий см. в разделе обработка и вызов событий. For more information about how to handle events, see Handling and Raising Events.

What is the command button on windows

Windows Controls: Command Buttons

Introduction to Command Buttons

Description

On a typical application, a button is an object that the user clicks to perform an action. To make this obvious, a button is a control surrounded by thick borders. Here is an example of a button on a form:

Although a control is usually positioned on a form, there various other control containers that can hold a button. These include the toolbar or the status bar, and the other containers we have used so far.

To indicate what it is used for, a button displays some text as its caption. A button can also display a picture instead. Another button can display both a string and a picture. When you create a button, you will decide what it should display and how it should behave.

Creating a Button

To support the buttons of an application, the .NET Framework provides an abstract class named ButtonBase. The regular button of Microsoft Windows is implemented by the Button class. At design time, to add a button to your project, from the Common Controls section of the Toolbox, you can click the Button and click the form or another container.

To programmatically create a button, you can declare a variable of type Button and use the new operator to allocate memory for it. Here is an example:

The Characteristics of a Button

The Caption of a Button

For a user, the most important aspects of a button are the message it displays and the action it performs. The text the button displays allows the user to know what the button is used for. This is represented by the Text property. The most popular strings that the buttons display are OK and Cancel. The OK caption is set for a form or a dialog box that informs the user of an error, an intermediary situation, or an acknowledgement of an action that was performed on the dialog that hosts the button. The Cancel caption is useful on a button whose main parent (the form or the dialog box) would ask a question or request a follow-up action from the user. Whenever a dialog box allows the user to dismiss it without continuing the action, you should provide a button with a Cancel caption.

After adding a button to a form (by design or with code), you can change its caption with code by assigning the desired string to the Text property. For example, you can change the caption of a button as follows:

After specifying the Text of a button, by default, it’s positioned in the middle center of the button:

The position of the text of a button is controlled through the TextAlign property which is a value of the ContentAlignment enumerator. The possible values are:

TopLeft	TopCenter	TopRight
MiddleLeft	MiddleCenter	MiddleRight
BottomLeft	BottomCenter	BottomRight

Here is an example:

The Image on a Button

Besides, or instead, of a caption, a button can display a picture on top. If you want a button to display a bitmap, you should first create, design, or have a picture. Then, in the Properties window, use the Image field to select a bitmap or an icon. You can also programmatically assign an Image object to the Image property. Here is an example:

This would produce:

By default, both the caption and the image display ion the middle-center of the button. To make them distinct and allow the user to see both, you can design a bitmap that has both and assign that bitmap as the image of the button. Alternatively, you can use a separate string and a separate picture. Fortunately, each can have its own alignment. We already saw how to control the alignment of the caption.

Besides displaying an image, the Button class is equipped with the ImageAlign property that allows you to specify the alignment of the image. The ImageAlign property is inherited from the ButtonBase class. The ButtonBase.ImageAlign property is based on the ContentAlignment enumeration that we are already familiar with. Here is an example:

This would produce:

Instead of using the Image property, you can first create an image list and add some pictures to it. Then, using the ImageList property, assign it to the button. Use the ImageIndex property to specify what picture would be displayed on the button.

The Flat Style of a Button

A regular button displays with raised borders as originally set by the operating system. To give your button a fancy look and behavior, you can use the FlatStyle property. The FlatStyle property is based on an enumeration of the same name. It provides 4 values that are:

Flat: The button appears flat. When the mouse is over it, it becomes highlighted

Popup: The button appears flat. When the mouse is over it, the borders of the button are raised

Standard: The button appears and behave like all regular buttons you have seen

System: The appearance of the button depends on the operating system

Obviously the most important and the most intuitive event of a button occurs when clicked. This event is of type EventArgs, which indicates that it doesn’t provide nor does it need any formal details about what is going on. To launch this event, you can double-click the button on the form. To create this event programmatically, first implement the method that would carry its assignment, then increment-add (with the += operator) it to the Click property of the button by assigning it the EventHandler constructor.

The Result of a Dialog Box

After the user has used a form or dialog box, to close it, the user would click a button. When the user does this, you must find out what button was clicked. Although there are various ways you can get this information, to assist you, the .NET Framework provides a convenient mechanism through an enumeration named DialogResult.

When creating a form or a dialog box, after adding a button, in the Properties window, click DialogResult and select on the values:

Except for None, by default, it does not matter what value you select but, you should follow Windows standard to select the right value.

After specifying the returned value of a button, access the properties of the form or dialog box:

• If you had selected OK as the DialogResult value of a button, you should select the name of that button for the AcceptButton property of the form
• If you had selected Cancel as the DialogResult value of a button, you should select the name of that button for the CancelButton property of the form

Command Buttons

This design guide was created for Windows 7 and has not been updated for newer versions of Windows. Much of the guidance still applies in principle, but the presentation and examples do not reflect our current design guidance.

With a command button, users initiate an immediate action.

A typical command button.

The default command button is invoked when users press the Enter key. It is assigned by the developer, but any command button becomes the default when users tab to it.

Guidelines related to layout are presented in a separate article.

Is this the right control?

To decide, consider these questions:

• Is the command button used to initiate an immediate action? If not, use another control.
• Would a link be a better choice? Use a link if:
  • The action is to navigate to another page, window, or Help topic. Exception: Wizard navigation uses Back and Next command buttons.
  • The command is embedded in a body of text.
  • The command is secondary in nature. That is, it does not relate to the primary purpose of the window. In this case, either a lightweight command button or link would be appropriate.
  • The command is part of a menu or group of related links.
  • The label is lengthy, consisting of five or more words, thus giving a command button an awkward appearance.
• Would a combination of radio buttons and generic command buttons be a better choice? Often radio buttons are used in conjunction with generic command buttons (OK, Cancel) in place of a set of specific command buttons when any of the following are true:

  There are five or more possible actions.

  Users need to view additional information before making a decision.

  Users need to interact with the choices (perhaps to see additional information) before making a decision.

  Users view the choices as options instead of different commands.

  Correct:

  In this example, radio buttons are combined with OK and Cancel buttons to provide additional information about the options.

  Incorrect:

  In this example, command buttons alone make it difficult for users to make an informed decision.

  Design concepts

  Using ellipses

  While command buttons are used for immediate actions, more information might be needed to perform the action. Indicate a command that needs additional information (including confirmation) by adding an ellipsis at the end of the button label.

  In this example, the Print. command displays a Print dialog box to gather more information.

  By contrast, in this example the Print command prints a single copy of a document to the default printer without any further user interaction.

  Proper use of ellipses is important to indicate that users can make further choices before performing the action, or even cancel the action entirely. The visual cue offered by an ellipsis allows users to explore your software without fear.

  This doesn’t mean you should use an ellipsis whenever an action displays another window only when additional information is required to perform the action. Consequently, any command button whose implicit verb is to «show another window» doesn’t take an ellipsis, such as with the commands About, Advanced, Help (or any other command linking to a Help topic), Options, Properties, or Settings.

  Generally, ellipses are used in user interfaces to indicate incompleteness. Commands that show other windows aren’t incomplete they must display another window and additional information isn’t needed to perform their action. This approach eliminates screen clutter in situations where ellipses have little value.

  Note: When determining if a command button needs an ellipsis, don’t use the need to elevate privileges as a factor. Elevation isn’t information needed to perform a command (rather, it’s for permission) and the need to elevate is indicated with the security shield.

  If you do only one thing. Use a concise, specific, self-explanatory label that clearly describes the action that the command button performs, and use an ellipsis when appropriate.

  Usage patterns

  Command buttons have several usage patterns:

  Standard command buttons You can use standard command buttons to initiate an immediate action.	A standard command button.
  Default command buttons The default command button in a window indicates the command button that will be activated when users press the Enter key.	A default command button. Any command button becomes the default when users tab to it. If the input focus is on a control that isn’t a command button, the command button with the default button attribute becomes the default. Only one command button in a window can be the default.
  Lightweight command buttons A lightweight command button is similar to a standard command button, except its button frame is shown only on mouse hover.	In this example, the command has a very lightweight appearance (similar to a link) until the user hovers over the command, at which point it is drawn with a button frame. You can use lightweight command buttons in situations where you would use a standard command button, but you want to avoid always showing the button frame. Lightweight command buttons are ideal for commands that you want to underemphasize and using a link wouldn’t be appropriate.
  Menu buttons Use a menu button when you need a menu for a small set of related commands.	A menu button with a small set of related commands. Use a menu button when a menu bar is undesirable, such as in a dialog box, toolbar, or other window that doesn’t have a menu bar. A single downward-pointing triangle indicates that clicking the button will drop down a menu.
  Split buttons Use a split button to consolidate a set of variations of a command, especially when one of the commands is used most of the time.	a collapsed split button. like a menu button, a single downward-pointing triangle indicates that clicking the rightmost portion of the button will drop down a menu. a dropped-down split button. in this example, a split button is used to consolidate six variations of the open command. the regular open command is used most of the time, so users normally don’t need to see the other commands. using a split button saves a significant amount of screen space, while also providing powerful choices. unlike a menu button, clicking the left portion of the button performs the action on the label directly. split buttons are effective in situations where the next action with a specific tool is likely to be the same as the last action. in this case, the label is changed to the last action, as with a color picker: In this example, the label is changed to the last action.
  Browse buttons Use a browse button to display a dialog box to help users select a valid value.	dialog boxes launched by a browse button help users select files, folders, computers, users, colors, and so on. they are typically combined with an unconstrained control such as a text box. they’re usually labeled browse, other, or more, and always have an ellipsis to indicate that more information is required. a text box with a browse button. for windows that have many browse buttons, you can use a short version: A short browse button.
  Progressive disclosure buttons Use a progressive disclosure button to show or hide infrequently used options.	hiding infrequently used options until they are needed is called progressive disclosure. double chevrons are used to indicate progressive disclosure, and they point in the direction in which the revealing or hiding will take place: after the button is clicked, its label changes to indicate that the next click will have the opposite effect: For more information and examples, see Progressive Disclosure Controls.
  Directional buttons Use a directional button to indicate the direction in which an action will take place.	in this case, a single angle bracket is used instead of a double chevron: A directional button indicates the direction of action.

  Guidelines

  General

  • Display a busy pointer if the result of clicking a command button isn’t instantaneous. Without feedback, users might assume that the click didn’t happen and click again.
  • If the same command button appears in more than one window, try to use the same label text and access key, and locate it in approximately the same place in each window when practical.
  • For command buttons with text labels, use a minimum button width and the standard command button height. For more information, see Recommended sizing and spacing.
  • For each window make the command buttons the same width. If that’s impractical, limit the number of different widths for command buttons with text labels to two.
  • When another control interoperates with a command button, such as a text box with a Browse button, denote the relationship by placing the command button in one of three places:
    • To the right of and top-aligned with the other control.
    • Below and left-aligned with the other control.
    • Vertically centered between controls that interoperate (such as Add and Remove buttons between two interoperating list boxes).
  • If multiple command buttons interoperate with the same control, vertically stack them to the right of and top-aligned with the other control, or horizontally place them left-aligned under the control.
  • When command buttons are subordinate to other controls, use the above placement and disable the subordinate command button until the superior control is selected.
  • Don’t use narrow, short, or tall command buttons with text labels because they tend to look unprofessional. Try to work with the default widths and heights.

  Correct:

  In this example, the button size is standard and looks professional.

  Incorrect:

  In this example, the button is too small.

  Incorrect:

  In this example, the button has too much space around the label.

  • Avoid combining text labels and graphics on command buttons. Combining text and graphics usually adds unnecessary visual clutter and does not improve the user’s comprehension. Consider combining text and graphics only when the graphic aids in comprehension, such as when it is a standard symbol for the command or it helps users visualize the results of the command. Otherwise, prefer text, but use either text or graphics.

  Correct:

  In this example, the arrow graphic helps users visualize the results of the command.

  Correct:

  In this example, standard symbols are combined with text to aid comprehension

  Incorrect:

  In this example, the cancel graphic adds nothing to the text.

  • Don’t use command buttons to set state. Use radio buttons or check boxes instead. Command buttons are only for initiating actions.

  Split buttons

  • Make the most likely command the default behavior. If there is more than one likely command, choose one that doesn’t require additional information.
  • If the most likely command is the last user selection, change the button label to the last selection.
  • Display the default command using bold text in the menu. Doing so makes it easier for users to find the default command, especially when the default command is dynamic or the split button uses a graphic instead of a text label.

  Default values

  • Include a default command button on every dialog box. Select the safest (to prevent loss of data or system access) and most secure command to be the default. If safety and security aren’t factors, select the most likely or convenient command.
  • Don’t make a destructive action the default command button unless there is an easy way to undo the command.

  Recommended sizing and spacing

  Recommended sizing and spacing for command buttons.

  Labels

  Label every command button.

  If the button has a graphic label only, assign its Name property to an appropriate text label. This enables assistive technology products such as screen readers to provide users with alternative information about the graphic.

  This example shows graphic buttons; internally, these buttons are labeled Previous, Next, and Copy.

  For short browse buttons (labeled «. «), the internal label should be Browse.

  Assign a unique access key. For guidelines, see Keyboard.

  Exceptions:

  • Don’t assign access keys to OK and Cancel buttons, because Enter is the access key for the default button (which is usually the OK button), and Esc is the access key for Cancel. Doing so makes the other access keys easier to assign.
  • Don’t assign access keys to short browse buttons (labeled «. «), because they can’t be assigned uniquely.

  Prefer specific labels over generic ones. Ideally users shouldn’t have to read anything else to understand the label. Users are far more likely to read command button labels than static text.

  • Exception: Don’t rename the Cancel button if the meaning of cancel is unambiguous. Users shouldn’t have to read all the buttons to determine which button cancels an action. However, rename Cancel if it is unclear what action is being canceled, such as when there are several pending actions.

  Acceptable:

  In this example, OK and Cancel are acceptable but unspecific labels.

  Better:

  In this example, Burn CD is more specific than OK.

  Incorrect:

  In this example, Cancel should be used instead of Don’t Burn CD.

  Start labels with an imperative verb and clearly describe the action that the button performs. Don’t use ending punctuation.

  • Exception: The following standard labels are acceptable without verbs: Advanced, Back, Details, Forward, Less, More, New, Next, No, OK, Options, Previous, Properties, Settings, and Yes.

  While short labels are preferred, use enough text to explain the command sufficiently. Use a direct object (a noun after the verb) when the object is not apparent from context. Ideally users shouldn’t have to read anything else to understand the label.

  Acceptable:

  In this example, a short label is acceptable if its meaning in context is readily apparent.

  Better: (if Add isn’t clear)

  In this example, adding a noun to the verb aids users’ comprehension.

  Best: (if Add or Add items aren’t clear)

  In this example, the label is self-explanatory.

  Use sentence-style capitalization. Doing so is more appropriate for Windows toneWindows tone and the use of short phrases for command buttons.

  • Exception: For legacy applications, you may use title-style capitalization if necessary to avoid mixing capitalization styles.

  Don’t use now in command button labels because the immediacy of the command can be taken for granted.

  • Exception: When necessary, use now to differentiate commands that start a task from commands that perform a task immediately.

  In this example, clicking the command button goes to a window or page that allows users to download.

  In this example, clicking the command button performs the download.

  Only one command in a task flow should be labeled with now. So, for example, a Download now command should never be followed by another Download now command.

  Don’t use later in command button labels if it implies an action that won’t happen. For example, don’t use Install later (in contrast to Install now) unless that command installs at a later time. Instead, use either Don’t install or Cancel.

  Incorrect:

  In this example, Restart Later incorrectly implies that command restarts automatically at a later time.

  Use an Advanced button only for options that are relevant to advanced users or require advanced user knowledge. Don’t use an Advanced button for features that are considered technologically advanced. For example, a printer’s stapling feature is not an advanced option, but its color management system is.

  Incorrect: (if the options really aren’t advanced)

  In this example, Advanced is misleading.

  Correct:

  In this example, the label is more specific and accurate.

  For command buttons that open other windows, choose a label that uses part or all of the secondary window’s title bar text. For example, a command button labeled Browse might open a dialog box entitled Browse for Folder. Using the same terminology throughout the task helps to keep users oriented.

  When asking a question, use labels that match the question. Don’t use OK/Cancel to answer Yes/No questions.

  Correct:

  In this example, the buttons answer the question.

  Incorrect:

  In this example, the buttons don’t answer the question.

  End the label with an ellipsis if the command requires additional information to execute.

  • Exception: Graphic labels don’t take an ellipsis.

  Correct: (if a Print options dialog is displayed)

  In this example, after the button is clicked, the Print options dialog is displayed and requires more information from the user.

  Don’t use an ellipsis when the successful completion of the action is simply to display another window. The following commands never take an ellipsis: About, Advanced, Options, Properties, Help.

  Incorrect:

  In this example, after the button is clicked, the Options dialog is displayed, but more information from the user is not required.

  In case of ambiguity (for example, the command label lacks a verb), decide based on the most likely user action. If simply viewing the window is a common action, don’t use an ellipsis.

  Correct:

  In the first example, users are most likely going to choose a color, so using an ellipses is correct. In the second example, users are most likely going to view the version information, making ellipses unnecessary.

  For browse buttons, use short browse buttons (labeled «. «) when there are more than two browse buttons in a window. Always use the short version when you want to display a browse button in a grid.

  For directional buttons, use a single angle bracket and have it point in the direction where the action takes place.

  The following table shows some common command button labels and their usage.

  Button label	Meaning	Access key
  Back	In wizards and task flows, go to the previous page.	‘B’
  Browse.	Display a dialog box to look for a file or object.	‘B’ or ‘r’
  Options	Display the choices available to users for customizing a program.	‘O’
  Pause	In progress dialog boxes, suspend the task.	‘P’
  Personalize	Customize a core experience that is crucial to the user’s personal identification with a program.	‘P’
  Preferences	Don’t use. Use Options instead.	Not applicable.
  Properties	Display the attributes and settings for an object.	‘P’ or first ‘r’
  Save	Save a group of settings, or save a file or object using its current name.	‘S’
  Save as.	Save a file or object using a specified name.	Second ‘a’
  Settings	Don’t use. Use Options instead.	Not applicable.
  Troubleshoot	Don’t use. Use a specific Help link instead.	Not applicable.

  For guidelines about commit button labels (OK, Cancel, Yes/No, Close, Stop, Apply, Next, Finish, Done), see User Interface Text.

  Documentation

  When referring to command buttons:

  • Use the exact label text, including its capitalization, but don’t include the access key underscore or ellipsis. Don’t include the word button.
  • To describe user interaction, use click.
  • When possible, format the label using bold text. Otherwise, put the label in quotation marks only if required to prevent confusion.

  Example: Click Print to print the document.

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