UIQ Controls - Command Button

This guide explains the UIQ control Command Button (CEikCommandButton). A Command Button can be used to invoke a command in an application, or to toggle one of its states. It may display a text label, an image, or both. Command buttons are divided into several different types as shown in the table below. All of the buttons are based on the Command Button base class.

This document focuses on the first Command Button in the table below, the Standard Command Button, which is the most commonly used Command Button and it shows what is specific for the different command buttons.

Standard Command Button (CEikCommandButton) A Command Button that can contain a text label, a picture or both. Two-picture Command Button (CEikTwoPictureCommandButton) A Standard Command Button that can hold a second picture, which is shown when the button is in a pressed state. Text Button (CEikTextButton) A Command Button that can only contain a text label. Bitmap Button (CEikBitmapButton) A Command Button that can only contain a picture. Menu Button (CEikMenuButton) A Standard Command Button with functionality to launch a Menu Pane when pressed.

The following functionality can be used by the application developer on all types of command buttons:

• Setting the behavior of the button:

  • Button remains in clear state,

  • Button remains in set state,

  • Button latches,

  • Button acts on pen-down events rather than on pen-up events,

• Setting the orientation of the components of the button, which are text label and bitmaps,

• Setting a bubble help text, which is displayed when the button is in a pressed state,

• Setting the button as a default button, which also gives the button a thicker border,

• Toggling between dimmed state and normal state,

• Changing border properties.

The following operations are applicable to the Standard Command Button:

• Changing the text label,

• Changing the bitmap picture.

Examples of Command Button graphics

Standard Command Button in clear unpressed state. Standard Command Button as a default button. The white frame shows that it is mapped to the Confirm key. Here the image is put on a grey background to make the frame visible. Standard Command Button in clear pressed state. Standard Command Button in clear dimmed state. Command Button in set unpressed state Command Button in set pressed state Command Button in set dimmed state Bitmap Button in clear unpressed state Button with text label

See the API documentation for Command Button CEikCommandButton.

The Command Button control is related to the Label and Menu Pane controls. See the How To guide for Label.

See even the API documentation for Label (CEikLabel) and Menu Pane (CEikMenuPane).

Command Buttons inherit from CEikCommandButtonBase, which inherits from CEikButtonBase.

This chapter explains how a Command Button control is constructed, used and destroyed. Source code examples are used and explained to illustrate how the Command Button control is used.

Use the following #include directive:

#include <eikcmbut.h>

Use the following LIBRARY directive in the project's mmp-file:

LIBRARY eikcoctl.lib

Resource files can be used to construct a Standard Command Button. The resource to use is defined by the CMBUT structure, defined in Uikon.rh. The structure looks like this:

STRUCT CMBUT
    {
    BYTE version = 0;
    WORD behavior = 0;
    WORD layout = 0;
    LTEXT helptxt = "";
    LLINK extension = 0;
    LTEXT txt = "";
    LTEXT bmpfile = "";
    WORD bmpid = 0xffff;
    WORD bmpmask = 0xffff;
    }

The values given in the structure definition are default values. The structure contains the following:

• version is not used,

• behavior sets button behavior flags,

• layout indicate flags that define how the horizontal space is handled between the button's text and image, ETextRightPictureLeft|EEikCmdButShareExcess,

• helptxt sets the help text for the button,

• extension is not used,

• txt specifies the button's text label. The default is an empty string,

• bmpfile states the bitmap filename from which to read the button's image. The default is eikon.mbm,

• bmpid gives the index of the bitmap in the bmpfile file. A default value of 0xffff indicates no bitmap.

• bmpmask specifies the index of the bitmap mask in the file. A default value of 0xffff indicates no bitmap mask.

The Command Button can have the following flags. The flags specified in the table are defined in EikCmBut.h:

Command Button - Resource flags

ETextRightPictureLeft Specifies the positions of text and image on the Command Button. Text and image are positioned horizontally with the text to the right of the image. ETextBottomPictureTop Text and image are positioned vertically with the text below the image. ETextTopPictureBottom Text and image are positioned vertically with the text above the image. ETextLeftPictureRight Text and image are positioned horizontally with the text to the left of the image. EShare Specifies how to share excess horizontal space between the Command Button's text and image. Here excess space is shared equally. EToText Excess space is allocated to the text only. EToPicture All excess space is allocated to the picture. ETextOnly Specifies whether text, image or both are to be displayed. Display text only. EPictureOnly Display image only. ETextAndPicture Display text and image.

This section discusses four different ways of constructing controls. The first three ways describe how to construct and add a control to the view of an application. The view framework is used in all three cases but in three different ways. The fourth way describes how to construct and launch a dialog from an application. The dialog framework constructs the control and adds it into the dialog.

A common way to construct controls is to specify them in the resource files and let the framework construct them from there. Specifying the controls in resource files is the preferred way of constructing controls since it allows for easier modifications compared to creating them entirely from source code.

This section covers different ways of constructing a Command Button.

3.3.1 Construction with View Framework Using Data from a Resource File

The example below describes how to construct a Command Button using the view framework.

The reason the example seems to be rather complex is because it demonstrates how to construct a complete view containing a Scrollable Container and a Layout Manager. It also encapsulates the Command Button in a Building Block. The view supports both pen and softkey styles; support of both styles in a view is optional.

1) Declare an enumeration for the controls to be used in the view in a *.hrh file. Hrh files are files to be included both in resource files (*.rss) and C++ files.

/* Declare the controls' ID in a *.hrh file for use both in resource and cpp */
enum TMyViewControls
    {
    EMyViewCommandButton,
    EMyViewScrollableContainer,
    EMyViewBuildingBlock,
    EMyViewNumberOfControls
    };

2) Declare the controls to be used in the view in your resource (*.rss) file:

/* Declare the set of controls to be used in the view */
RESOURCE QIK_CONTROL_COLLECTION r_my_command_button_view_controls
    {
    items =
        {
        QIK_CONTROL
            {
            unique_handle = EMyViewScrollableContainer;
            type = EQikCtScrollableContainer;
            control = r_my_command_button_scroll_pane;
            },
        QIK_CONTROL
            {
            unique_handle = EMyViewBuildingBlock;
            type = EQikCtCaptionedTwolineBuildingBlock;
            control = r_my_command_button_building_block;
            },
        QIK_CONTROL
            {
            unique_handle = EMyViewCommandButton;
            type = EEikCtCommandButton;
            control = r_my_command_button;
            }
        };
    }

3) Define the view and its contents in your resource file:

/* The view */
RESOURCE QIK_VIEW r_my_command_button_view
    {
    pages = r_my_command_button_viewpages;
    }
                
/* The view page */
RESOURCE QIK_VIEW_PAGES r_my_command_button_viewpages
    {
    pages =
        {
        QIK_VIEW_PAGE
            {
            container_unique_handle = EMyViewScrollableContainer;
            page_content = r_my_command_button_view_container_details;
            }
        };
    }

4) Define the resource for the Scrollable Container used in the view:

/* The scrollable container used in the view */
RESOURCE QIK_SCROLLABLE_CONTAINER r_my_command_button_scroll_pane
    {
    }

5) Declare the contents and properties for the Scrollable Container used in the view:

/* Contents of the scrollable container used in the view */
RESOURCE QIK_SCROLLABLE_CONTAINER_SETTINGS r_my_command_button_view_container_details
    {
    controls =
        {
        QIK_CONTAINER_ITEM
            {
            unique_handle = EMyViewBuildingBlock;
            }
        };
    }

6) Define the control resource structure used in the view:

/* The Command Button used in the view */   
RESOURCE CMBUT r_my_command_button
    {
    txt = "Command Button";
    }

7) Define the settings for the Building Block containing the control:

/* Settings for the EQikCtCaptionedTwolineBuildingBlock containing the Command Button */
RESOURCE QIK_SYSTEM_BUILDING_BLOCK r_my_command_button_building_block
    {
    content =
        {
        QIK_SLOT_CONTENT
            {
            slot_id = EQikItemSlot1;
            caption = "Choose:";
            },
        QIK_SLOT_CONTENT
            {
            slot_id = EQikItemSlot2;
            unique_handle = EMyViewCommandButton;
            }
        };
    }

8) The configurations of the view:

RESOURCE QIK_VIEW_CONFIGURATIONS r_my_command_button_ui_configurations
    {
    configurations=
        {
        QIK_VIEW_CONFIGURATION
            {
            ui_config_mode = KQikSoftkeyStylePortrait;
            view = r_my_command_button_view;
            command_list = r_my_command_button_commands;
            },
        QIK_VIEW_CONFIGURATION
            {
            ui_config_mode = KQikPenStyleTouchPortrait;
            view = r_my_command_button_view;
            command_list = r_my_command_button_commands;
            }   
        };
    }

9) The command list for the view:

RESOURCE QIK_COMMAND_LIST r_my_command_button_commands
    {
    items =
        {
        // This command shall only be visible in debug mode because it is only
        // used to find memory leaks during development of the application.
        QIK_COMMAND
            {
            id = EEikCmdExit;
            type = EQikCommandTypeScreen;
            // Indicate that this command will only be visible in debug
            stateFlags = EQikCmdFlagDebugOnly;
            text = "Close (debug)";
            }
        };
    }

10) The view framework constructs the view described in this example with this code:

void CMySinglePageView::ViewConstructL()
    {
    ViewConstructFromResourceL(R_MY_COMMAND_BUTTON_UI_CONFIGURATIONS, R_MY_COMMAND_BUTTON_VIEW_CONTROLS);
    }

11) The result should look something like this:

3.3.2 Construction with Your Own C++ Code Using Data from a Resource File

The example below describes how to construct a Command Button from resource with your own C++ code.

The reason the example seems to be rather complex is because it demonstrates how to construct a complete view containing a Scrollable Container and a Layout Manager. It also encapsulates the Command Button in a Building Block.

This example uses the resource structures from the previous example. The following code creates the Command Button:

#include <QikBuildingBlock.h>
#include <QikRowLayoutManager.h>
#include <QikGridLayoutManager.h>
#include <eikcmbut.h>
                    
void CMySinglePageView::ViewConstructL()
    {
    // Give a layout manager to the view
    CQikGridLayoutManager* gl = CQikGridLayoutManager::NewLC();
    SetLayoutManagerL(gl);
    CleanupStack::Pop(gl);
                        
    // Create a container and give it to the view
    ControlProvider()->ControlInfos().AddFromResourceL(R_MY_COMMAND_BUTTON_VIEW_CONTROLS);
    CCoeControl* ctrl = ControlProvider()->ControlConstructIfNeededL(EScrollableContainer, *this);
                        
    ASSERT(ctrl);
    CQikContainerBase* container;
    ctrl->MopGetObjectNoChaining(container);
    ASSERT(container);
    Controls().AppendLC(container);
    CleanupStack::Pop(ctrl);
                        
    // Create a layout manager to be used inside the container
    CQikRowLayoutManager* rowlayout = CQikRowLayoutManager::NewLC();
    container->SetLayoutManagerL(rowlayout);
    CleanupStack::Pop(rowlayout);
                        
    // Create the building block (containing a Command Button) and add it to the container
    CQikBuildingBlock* block = CQikBuildingBlock::CreateSystemBuildingBlockL(EQikCtCaptionedTwolineBuildingBlock);
    container->AddControlLC(block, EMyViewBuildingBlock);
    TResourceReader blockReader;
    iCoeEnv->CreateResourceReaderLC(blockReader,R_MY_COMMAND_BUTTON_BUILDING_BLOCK);
    block->ConstructFromResourceL(blockReader, *ControlProvider());
    CleanupStack::PopAndDestroy(); //blockReader
    CleanupStack::Pop(block);
    }

What the code does

1) Initializes the Command Manager with an empty Command List. The controls placed in the view add their commands to the Command List when they receive focus.

2) Creates a Layout Manager for the view. The Grid Layout Manager fills the view with its only control in this example, the Scrollable Container.

3) Loads the control collection R_MY_VIEW_CONTROLS into the Control Provider. Then the Control Provider is asked to create the Scrollable Container.

4) Uses the MopGetObjectNoChaining function to determine whether the control that was created really is a class of the type CQikContainerBase before it is added to the view.

5) Creates a Layout Manager to control the layout inside the container. Adds the Layout Manager to the container.

6) Constructs the Building Block containing the Command Button from the resource R_MY_BUILDING_BLOCK. Adds the Building Block to the container.

The Command Button can also be created without a Building Block. In that case, replace the last section in the code above, from the "Create building block..." comment, with the following code.

Since a pointer to the control is declared here, eikcmbut.h needs to be included in the cpp-file and eikcoctl.lib in the mmp-file.

// Create the Command Button and add it to container
TResourceReader reader;
iEikonEnv->CreateResourceReaderLC(reader, R_MY_COMMAND_BUTTON);
CEikCommandButton* cmdbutton = new (ELeave) CEikCommandButton();
container->AddControlLC(rted, EMyViewCommandButton);
cmdbutton->ConstructFromResourceL(reader);
cmdbutton->SetUniqueHandle(EMyViewCommandButton);
CleanupStack::Pop(cmdbutton);
CleanupStack::PopAndDestroy(); //reader

Use AddControlLC to add controls to a Scrollable Container. Add the controls as soon as they are created. Do not push them onto the Cleanup Stack before they are added. Do not pop them from the Cleanup Stack until they are fully constructed. A TCleanupItem created in AddControlLC will make sure that the control is both cleaned up and removed from the Components Array if a leave occurs before the control is fully constructed.

3.3.3 Construction Solely from C++ Code

The example below describes how to construct a Command Button solely from C++ code.

The reason the example seems to be rather complex is because it demonstrates how to construct a complete view containing a Scrollable Container and a Layout Manager.

The following source code constructs a Command Button:

#include <QikScrollableContainer.h>
#include <QikRowLayoutManager.h>
#include <QikGridLayoutManager.h>
#include <QikBuildingBlock.h>
#include <eikcmbut.h>

void CMySinglePageView::ViewConstructL()
    {
                    
    // Give a layout manager to the view
    CQikGridLayoutManager* gridlayout = CQikGridLayoutManager::NewLC();
    SetLayoutManagerL(gridlayout);
    CleanupStack::Pop(gridlayout);
                        
    // Create a container and add it to the view
    CQikScrollableContainer* container = new (ELeave) CQikScrollableContainer();
    Controls().AppendLC(container);
    container->ConstructL(EFalse);
    CleanupStack::Pop(container);
                        
    // Create a layout manager to be used inside the container
    CQikRowLayoutManager* rowlayout = CQikRowLayoutManager::NewLC();
    container->SetLayoutManagerL(rowlayout);
    CleanupStack::Pop(rowlayout);
                    
    // Create the Command Button and add it to the container
    CEikCommandButton* cmdbutton = new (ELeave) CEikCommandButton();
    container->AddControlLC(cmdbutton, EMyViewCommandButton);
    cmdbutton->SetTextL(_L("Command Button!"));
    cmdbutton->SetObserver(this);
    cmdbutton->SetUniqueHandle(EMyViewCommandButton);
    CleanupStack::Pop(cmdbutton);
    }

What the code does

1) Initializes the Command Manager with an empty Command List. The controls placed in the view add their commands to the Command List when they receive focus.

2) Creates a Layout Manager for the view. The Grid Layout Manager fills the view with its only control in this example, the Scrollable Container.

3) Instantiates a container and adds it to the view.

4) Creates a Layout Manager and adds it to the container.

5) Creates the Command Button control from C++ code. Sets the view, this, to be an observer of the Command Button. The view's base class, CQikViewBase, handles focus changes in its method HandleControlEventL. For more details see the section below on how to be notified with Control Events.

3.3.4 Construction with the Dialog Framework Using Data from a Resource File

Command Button can be constructed from resource files in dialogs as well. To construct a dialog from resource a valid resource definition of that dialog must be in one of the project's resource files.

An example of a dialog resource containing the control is given below. For more information about the dialog class and its resource structure see CEikDialog and DIALOG in the API documentation.

1) Declare a dialog resource containing the Command Button control:

RESOURCE DIALOG r_commandbuttons_test_dialog
    {
    title="Command Buttons Test";
    command_list= r_dialog_commands;
    flags=EEikDialogFlagWait;
    items=
        {
        DLG_LINE
            {
            prompt="Command button";
            type=EEikCtCommandButton;
            control=CMBUT
                {
                txt="Command Button";
                };
            }
        };
    }

The resource properties inside the Control Block are the same as the ones described in the previous section.

2) Launch the dialog using the following source code. The dialog resource ID is passed as an argument:

CEikDialog* dlg = new (ELeave) CEikDialog();
dlg->ExecuteLD(R_COMMANDBUTTONS_TEST_DIALOG);

The function returns immediately if EEikDialogFlagWait has not been specified in the dialog resource. If EEikDialogFlagWait is specified it returns when the dialog exits. The dialog framework will in both situations delete the dialog appropriately as indicated by the D suffix of the ExcecuteLD function name.

This section covers the most common functions used for interacting with the control.

When constructing the control with resource data, no reference to the control is available in the view class. When constructing the control with code, the preferred way might be to not save a reference to the control. In both these cases, the LocateControlByUniqueHandle function is used to get a pointer to the control by supplying the control's unique handle. When constructing the view and the control from code, you must explicitly set this unique handle by calling the method SetUniqueHandle. See the code examples below.

Note that the function will return NULL if the control could not be found. Always check the pointer before using it!

// Set the unique handle
commandbutton->SetUniqueHandle(EMyViewCommandButton);
                
// Get a pointer to the Command Button
CEikCommandButton* commandbutton = LocateControlByUniqueHandle<CEikCommandButton>(EMyViewCommandButton);

3.4.1 How to be Notified with Control Events

In order to be notified when the Command Button changes state you must add an observer to the Command Button. An observer is an object of the type MCoeControlObserver. The observer will then receive a function call to its function HandleControlEventL(CCoeControl* aControl, TCoeEvent aEventType) when the Command Button changes state.

The view base class, CQikViewBase, implements the MCoeControlObserver. The HandleControlEventL function must be overloaded in the view class, because the view inherits from CQikViewBase.

The following source code example shows how to add an object as an observer and how to receive events from the Command Button:

void CMySinglePageView::ViewConstructL()
    {
    // Construction code
    …
    // Adding this object as an observer
    commandbutton->SetObserver(this);
    }
                            
void CMySinglePageView::HandleControlEventL(CCoeControl* aControl, TCoeEvent aEventType)
    {
    // Call base class to get focus navigation right
    CQikViewBase::HandleControlEventL(aControl, aEventType);

    CEikCommandButton* commandbutton = LocateControlByUniqueHandle<CEikCommandButton>(EMyViewCommandButton);

    if (aControl == commandbutton)
        {
        switch(aEventType)
            {
            case EEventStateChanged:
                // The internal state of the Command Button was changed.
                break;
                                        
            case EEventRequestExit:
                break;
                                        
            case EEventRequestCancel:
                break;
                                        
            case EEventRequestFocus:
                // The Command Button received a pointer down event
                break;
                                        
            case EEventPrepareFocusTransition:
                // A focus change is about to appear
                break;
                                    
            case EEventInteractionRefused:
                // The Command Button is dimmed and received a pointer down event.
                break;
                                    
            default:
                break;
            }
        }
    }

The reason for calling the base class's HandleControlEventL function is that the view base class CQikViewBase handles focus management between controls in the view. If the Command Button observer is not a class which derives from CQikViewBase, focus management must be resolved by the observer itself. If a control requests focus and does not get it from the observer, it will generate a panic in some cases if the observer does not leave.

For more details on the TCoeEvent type, see class MCoeControlObserver in the API documentation.

Destroying the control is just a matter of invoking operator delete on the Command Button object.

Subclassing Command Button is not recommended.