在Android中如何使用注解取代Enum

小咪咪 2022-07-21 01:46 171阅读 0赞

# 在Android中如何使用注解取代Enum #

### Android中定义了许多的注解，如@IdRes,@LayoutRes…可以帮助我们在传递参数时，避免参数传递出错。当然我们也可以通过枚举定义参数，也可以达到相同效果。在Android中，系统为我们定义好了2个注解，@IntDef和@StringDef,具体代码如下所示： ###

Test类定义好注解

public class Test { 
    
        public static final int A = 0;
        public static final int B = 1;
        public static final int C = 2;
        public static final int D = 3;
        public static final String E = "E";
        public static final String F = "F";
        public static final String G = "G";
        public static final String H = "H";
    
        @IntDef({A, B, C, D})
        @Retention(RetentionPolicy.SOURCE)
        public @interface FormatInt { 
    
        }
    
        @StringDef({E, F, G, H})
        @Retention(RetentionPolicy.SOURCE) 
        public @interface FormatString { 
    
        }
    }

public class MainActivity extends AppCompatActivity { 
    
       public class MainActivity extends AppCompatActivity { 
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            int format = getInt(Test.A);
    
            String f = getString(Test.E);
    
        }
    
        //在方法参数上使用注解
        public int getInt(@Test.FormatInt int format) {
            return format;
        }
    
        public String getString(@Test.FormatString String format) {
            return format;
        }
    }

@IntDef注解的代码

@Retention(SOURCE)
    @Target({ANNOTATION_TYPE})
    public @interface IntDef { 
        /** Defines the allowed constants for this element */
        long[] value() default {};
    
        /** Defines whether the constants can be used as a flag, or just as an enum (the default) */
        boolean flag() default false;
    }

@StringDef的注解代码

@Retention(SOURCE)
    @Target({ANNOTATION_TYPE})
    public @interface StringDef { 
        /** Defines the allowed constants for this element */
        String[] value() default {};
    }