ComposableTarget

  • Cmn
    @Retention(value = AnnotationRetention.BINARY)
    @Target(allowedTargets = [AnnotationTarget.FILE, AnnotationTarget.CLASS, AnnotationTarget.FUNCTION, AnnotationTarget.PROPERTY_GETTER, AnnotationTarget.TYPE, AnnotationTarget.TYPE_PARAMETER])
    annotation ComposableTarget

The Composable function is declared to expect an applier with the name applier. The applier name can be an arbitrary string but is expected to be a fully qualified name of a class that is annotated by ComposableTargetMarker containing a descriptive name to be used in diagnostic messages.

The applier name is used in diagnostic messages but, if it refers to a marked annotation, ComposableTargetMarker.description is used instead of the class name.

The Compose compiler plugin can, in most cases, infer this or an equivalent ComposableInferredTarget, for composable functions. For example, if a composable function calls another composable function then both must be of the same group of composable functions (that is, have declared or inferred the same applier value). This means that, if the function called is already determined to be in a group, them the function that calls it must also be in the same group. If two functions are called of different groups then the Compose compiler plugin will generate an diagnostic message describing which group was received and which group was expected.

The grouping of composable functions corresponds to the instance of Applier that is required to be used by the Composer to apply changes to the composition. The Applier is checked at runtime to ensure the Applier that is expected by a composable function is the one supplied at runtime. This annotation, and the corresponding validation performed by the Compose compiler plugin, can detect mismatches at compile time, and issue a diagnostic message when calling a Composable function will result in the Applier check failing.

In most cases this annotation can be inferred. However, this annotation is required for Composable functions that call ComposeNode directly, for abstract methods, such as interfaces functions (which do not contain a body from which the plugin can infer the annotation), when using a composable lambda in sub-composition, or when a composable lambda is stored in a class field or global variable.

Leaving the annotation off in such cases will result in the compiler ignoring the function and it will not emit the diagnostic when the function is called incorrectly.

Summary

Public constructors
Cmn

Public properties
String

The applier name used during composable call checking.
Cmn

Public constructors

ComposableTarget

Cmn 
ComposableTarget(applier: String)
Parameters
applier: String

The applier name used during composable call checking. This is usually inferred by the compiler. This can be an arbitrary string value but is expected to be a fully qualified name of a class that is marked with ComposableTargetMarker.

Public properties

applier

Cmn 
val applier: String

The applier name used during composable call checking. This is usually inferred by the compiler. This can be an arbitrary string value but is expected to be a fully qualified name of a class that is marked with ComposableTargetMarker.