Display-only components
These show a value and nothing else: no input, no focus, no change event. They exist because a screen that may not be edited should not look like a screen that may be - a row of greyed-out input boxes reads as "you are not allowed to", where plain text reads as "this is what it is".
The components
| Component | Shows |
|---|---|
DisplaySpan<T> |
any value, converted or rendered, as a span |
DisplayControl<T> |
the same as a div, so it lines up in a form |
DisplayCheckbox |
a Boolean as a tick box picture |
DisplayRadiobutton |
a Boolean as a radio button icon |
DisplayHtml |
html, with the parts it does not allow taken out |
PercentageCompleteRuler2 |
how far something got, as a bar |
EmbeddedCode |
a piece of code, as code |
What a display control is
All of them except the last two implement IDisplayControl<T>, which is nothing
but IControl<T> with a marker on it. That means they fit everywhere a control
fits - a form builder takes them, a table cell holds them - while behaving as
you would expect of something that cannot be edited:
| Asked | A display control answers |
|---|---|
getValue() |
exactly what setValue() was given |
getValueSafe() |
the same - it cannot fail |
isReadOnly() |
true, always; setReadOnly() does nothing |
isDisabled(), isMandatory() |
false; their setters do nothing |
getOnValueChanged() |
null - the value only changes when the code changes it |
There is nothing to validate, so nothing can report an error, and nothing arrives from the browser: a display control renders and that is all.
Read-only control, or display control?
Most input controls have a read-only state of their own, and several of them
already render as plain text when they are in it - a
ComboFixed2 shows the label of its
value, a LookupInput2 shows
the record. Prefer that when a screen switches between editing and viewing: one
control, one binding, one line of code deciding.
Reach for a display component when the value is never editable on this screen: a total that is computed, a state the user cannot change, a review written by somebody else. The result reads better, and nothing about the control suggests otherwise.