Text Class: Buttons, Textfields, Labels
From MorphOS Library
Grzegorz Kraszewski
This article in other languages: Polish
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Textfields
A textfield is a read-only framed area showing some (usually changing at runtime) text. The difference between a label and a textfield is that the latter has a frame and a background specified:
MUIA_Frame, MUIV_Frame_Text, MUIA_Background, MUII_TextBack,
Buttons
A text button is an instance of the Text class too. It has more attributes than a plain label however, because it handles user input. MUI has a predefined background and frame for buttons:
MUIA_Frame, MUIV_Frame_Button, MUIA_Background, MUII_ButtonBack,
These attributes also specify a frame and background for the "pressed" state. MUI also has separate font settings for buttons. Forgetting the MUIA_Font attribute for buttons is one of most common errors in MUI design.
MUIA_Font, MUIV_Font_Button,
Many users (and programmers) just have the default font defined for buttons, so the bug is not visible. It is recommended to always test a GUI with some unusual font settings for buttons, so the problem is easily visible. Button text is usually centered, which may be done either by inserting the "\33c" sequence at the start of the button label, or using MUIA_Text_PreParse.
MUIA_Text_PreParse, "\33c",
After definition of the button appearance it is time to handle user input. The button behaviour is defined by the MUIA_InputMode attribute with three values:
- MUIV_InputMode_None – The default value, button does not react on anything.
- MUIV_InputMode_RelVerify – A simple pushbutton activated by a left mouse button click.
- MUIV_InputMode_Toggle – A two-state button, one click switches it on, another one switches it off.
Another common bug with MUI buttons is to omit keyboard handling. The mouse is not everything. The first, obligatory step is to enter the button into the window's TAB key cycle chain:
MUIA_CycleChain, TRUE,
Any gadget entered into the chain may be selected by pressing the TAB key (for default MUI keyboard settings). The selected object has a special frame drawn around it. Then it may be activated by some key set in MUI preferences. For buttons the default "pressing" key is the return key. A rule of thumb for cycle chaining:
Another keyboard handling feature provided by MUI is hotkeys. A hotkey just activates a button associated to it. Hotkeys have the following features:
- MUI provides a visual hint of a button hotkey by underlining the hotkey letter in the button label. It implies that the hotkey letter must exist in the label.
- There is visual feedback for using a hotkey, the button is pressed as if it has been clicked with the mouse.
Not every button in a GUI has to have a hotkey. The best practice is to assign hotkeys only for the most used buttons, especially if there are many buttons in a window. A hotkey is defined with two attributes:
- MUIA_Text_HiChar – this attribute specifies a letter to be underlined in the label. It is case insensitive.
- MUIA_ControlChar – this attribute specifies a hotkey. Of course it should be the same as the above one. It should be a lowercase letter, as uppercase forces a user to press SHIFT, making the hotkey less comfortable to use. There is also no visual hint for SHIFT requirement. Digits may be also used as hotkeys if the label contains them. Using punctuation and other characters should be avoided. An example of use:
MUIA_Text_Contents, "Destroy All", MUIA_Text_HiChar, 'a', MUIA_Text_ControlChar, 'a'
Note that these attributes take a single char, not a string.