注解

定義數(shù)據(jù)

companion object {
        const val RESOUCES_ONE = 1;
        const val RESOUCES_TWO = 2;
    }

定義數(shù)據(jù)

@IntDef({MainActivity.RESOUCES_ONE,MainActivity.RESOUCES_TWO})
@Target({ElementType.FIELD,ElementType.PARAMETER})
@Retention(RetentionPolicy.SOURCE)
public @interface AnnotateValue {
}

輸入錯誤會提示

錯誤提示

下面解釋

@Target:注解的作用目標(biāo)

public enum ElementType {
    /** Class, interface (including annotation type), or enum declaration */
    TYPE,

    /** Field declaration (includes enum constants) */
    FIELD,

    /** Method declaration */
    METHOD,

    /** Formal parameter declaration */
    PARAMETER,

    /** Constructor declaration */
    CONSTRUCTOR,

    /** Local variable declaration */
    LOCAL_VARIABLE,

    /** Annotation type declaration */
    ANNOTATION_TYPE,

    /** Package declaration */
    PACKAGE,

    /**
     * Type parameter declaration
     *
     * @since 1.8
     */
    TYPE_PARAMETER,

    /**
     * Use of a type
     *
     * @since 1.8
     */
    TYPE_USE,

    /**
     * Module declaration.
     *
     * @since 9
     */
    MODULE
}

  @Target(ElementType.TYPE)——接口、類、枚舉、注解
  @Target(ElementType.FIELD)——字段、枚舉的常量
  @Target(ElementType.METHOD)——方法
  @Target(ElementType.PARAMETER)——方法參數(shù)
  @Target(ElementType.CONSTRUCTOR) ——構(gòu)造函數(shù)
  @Target(ElementType.LOCAL_VARIABLE)——局部變量
  @Target(ElementType.ANNOTATION_TYPE)——注解
  @Target(ElementType.PACKAGE)——包

@Retention：注解的保留位置

public enum RetentionPolicy {
    /**
     * Annotations are to be discarded by the compiler.
     */
    SOURCE,

    /**
     * Annotations are to be recorded in the class file by the compiler
     * but need not be retained by the VM at run time.  This is the default
     * behavior.
     */
    CLASS,

    /**
     * Annotations are to be recorded in the class file by the compiler and
     * retained by the VM at run time, so they may be read reflectively.
     *
     * @see java.lang.reflect.AnnotatedElement
     */
    RUNTIME
}

RetentionPolicy.SOURCE:這種類型的Annotations只在源代碼級別保留,編譯時 就會被忽略,在class字節(jié)碼文件中不包含。
RetentionPolicy.CLASS:這種類型的Annotations編譯時被保留,默認(rèn)的保留策略,在class文件中存在,但JVM將會忽略,運行時無法獲得。
RetentionPolicy.RUNTIME:這種類型的Annotations將被JVM保留,所以他們能在運行時被JVM或其他使用反射機制的代碼所讀取和使用。

@Document：說明該注解將被包含在javadoc中

@Inherited：說明子類可以繼承父類中的該注解

總結(jié)：

三個值中SOURCE < CLASS < RUNTIME，即CLASS包含了SOURCE，RUNTIME包含SOURCE、CLASS

反射

下面先看代碼

 public static void injectView(Activity activity) {
        //獲取class
        Class<? extends Activity> cla = activity.getClass();
        //獲取對應(yīng)class下所有屬性
        Field[] fields = cla.getDeclaredFields();
        for (Field field : fields) {
            //判斷是否有我們注解
            boolean isEsite = field.isAnnotationPresent(AnnotateFindView.class);
            if (isEsite) {
                AnnotateFindView annotation = field.getAnnotation(AnnotateFindView.class);
                int idResource = annotation.value();
                View view = activity.findViewById(idResource);
                field.setAccessible(true);
                try {
                    field.set(activity, view);
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }
            }
        }

    }

結(jié)合注解就可以省略getIntent

//創(chuàng)建注解
@Target({ElementType.FIELD,ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
public @interface ActivityValue {
    String value() default "";
}
//反射賦值
public static void injntActivity(Activity activity) {
        Class<? extends Activity> cla = activity.getClass();

        Intent intent = activity.getIntent();
        Bundle extras = intent.getExtras();

        if (extras == null) {
            return;
        }
        Field[] fields = cla.getDeclaredFields();

        for (Field field : fields) {
            boolean isExsit = field.isAnnotationPresent(ActivityValue.class);
            if (isExsit) {
                ActivityValue annotation = field.getAnnotation(ActivityValue.class);
                String key = TextUtils.isEmpty(annotation.value()) ? field.getName() : annotation.value();
                Object obj = extras.get(key);
                Class<?> type = field.getType().getComponentType();
                if (field.getType().isArray() &&null!=type&& Parcelable.class.isAssignableFrom(type)) {
                    Object[] objs = (Object[]) obj;
                    Class<? extends Object[]> clas = (Class<? extends Object[]>) field.getType();
                    obj = Arrays.copyOf(objs, objs.length, clas);
                }

                field.setAccessible(true);
                try {
                    field.set(activity, obj);
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                }

            }
        }

    }
//跳轉(zhuǎn)
    mainActivity.btnStartIntent.setOnClickListener {
            val vo = UserData().apply {
                age = 2
                name = "小馬哥"
                cla = "一年級二班"
            }
            val intent = Intent(this, ContentActivity::class.java).apply {
                putExtra("name", "小明")
                putExtra("age", 1)
                putExtra("vo", vo)
            }
            startActivity(intent)
        }

   

在跳轉(zhuǎn)的ContentActivity 注解以下就可以了

 @ActivityValue
    var name: String? = null;

    @ActivityValue
    var age: Int? = null;

    @ActivityValue(value = "vo")
    var dataVo: UserData? = null;

結(jié)合上面就可以擴展個別控件設(shè)置背景