In the following example, the
color property of Rectangle depends on the
pressed property of TapHandler . This relationship is described using a conditional expression:
There are two ways to define a property binding: the most common one is shown in the example earlier, in a property initialization . The second (and much rarer) way is to assign the property a function returned from the
See the property bindings documentation for more information about how to define property bindings, and see the documentation about Property Assignment versus Property Binding for information about how bindings differ from value assignments.
QML object types can emit signals in reaction to certain events occurring. Those signals can be handled by signal handler functions, which can be defined by clients to implement custom program logic.
Suppose that a button represented by a Rectangle type has a TapHandler and a Text label. The TapHandler emits its
tapped signal when the user presses the button. The clients can react to the signal in the
For more details about signals and signal handlers, refer to the following topics:
Signal and Handler Event System
An example of an inline custom method is as follows:
The fibonacci function is run whenever the TapHandler emits a
import statement, like the QML modules .
For example, the
fibonacci() method in the earlier example could be moved into an external file named
fib.js, and accessed like this:
QML object types that emit signals also provide default signal handlers for their signals, as described in the previous section. Sometimes, however, a client wants to trigger a function defined in a QML object when another QML object emits a signal. Such scenarios can be handled by a signal connection.
tapped signal to the
jsFunction() is called whenever the TapHandler ‘s
tapped signal is emitted.
See Connecting Signals to Methods and Signals for more information.
A QML object emits the
Component.onCompleted handler runs after the object is instantiated. Thus, the best place to write application startup code is in the
Component.onCompleted handler of the top-level object, because this object emits
Component.completed when the QML environment is fully established.
Any object in a QML file - including nested objects and nested QML component instances - can use this attached property. If there is more than one
onCompleted() handler to execute at startup, they are run sequentially in an undefined order.
Component emits a
destruction() signal just before being destroyed.