How to use a custom annotation in the J2Objc Annotations framework

The use of custom annotations in the J2OBJC annotation framework can easily convert Java code to Objective-C code.This article will show you how to define and use custom annotations. First, let's define a custom annotation.You can use the @Interface keyword to create a definition of an annotation and use the retaining strategy of specified the annotation specified by the @RETENTION annotation.The following is an example: import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; @Retention(RetentionPolicy.CLASS) @Target({ElementType.TYPE, ElementType.METHOD}) public @interface MyCustomAnnotation { String name(); int version() default 1; } In the above example, we define an annotation called @Mycustomannotion.It has two member variables: name and version.The name variable is a string type, and the Version variable is an integer type.We also provide a default value 1 for the Version variable. Next, let's see how to use the custom annotations we defined in the code.The following is an example: @MyCustomAnnotation(name = "MyApp", version = 2) public class MyClass { @MyCustomAnnotation(name = "myMethod", version = 1) public void myMethod() { // Some code here... } } In the above example, we used @Mycustomannotation annotations on the MyClass class and MyMethod methods.We provide the corresponding parameter values for annotations. After using a custom annotation, you can use the J2ONC tool to convert the Java code to Objective-C code.In the conversion Objective-C code, we can access the member variable value by calling the API provided by J2Objc.For example, in the Objective-C, you can use the Objc_Method Macro to obtain the variable value of the notification method, as shown below: objectivec #include "MyClass.h" J2OBJC_Void __attribute__((used)) MyMethod(MyClass *self, SEL _cmd) { // Get annotation instance MyCustomAnnotation *annotation = [self.class myCustomAnnotationFor_myMethod]; // Get annotation values NSString *name = annotation.name; int version = annotation.version; // Print annotation values NSLog(@"Name: %@, Version: %d", name, version); } In the above Objective-C code, we first use the [Self.class MyCustomannotationfor_MyMethod] method to obtain the annotation example, and then use the member variable access access to the member variable to obtain the value of the member variable. This is the basic process of using custom annotations in J2OBJC's annotation framework.By using custom annotations, you can add more metadata information to the Java code and access and process after converting to Objective-C code.