java基础 注解 android中的实现

先贴实现的activity的代码：

@ContentView(R.layout.activity_main)public class MainActivity extends AppCompatActivity {    @ViewInject(R.id.text_view)    private TextView textView;    @OnClick(R.id.text_view)    private void onClick(View view){        textView.setText("我是click后的textview");    }    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        ViewInjectUtils.inject(this);        textView.setText("我是click前的textview");    }}

ContentView（类）注解实现：

1、定义注解

                @Target(ElementType.TYPE)                @Retention(RetentionPolicy.RUNTIME)                public @interface ContentView {                    int value();                }

2、实现注解

private static void injectContentView(Activity activity) {       Class<? extends Activity> clazz = activity.getClass();       ContentView contentView = clazz.getAnnotation(ContentView.class);        if (contentView != null) {            //如果这个activity上面存在这个注解的话，就取出这个注解对应的value值，其实就是前面说的布局文件。            int layoutId = contentView.value();            try {                Method setViewMethod = clazz.getMethod("setContentView", int.class);                setViewMethod.invoke(activity, layoutId);            } catch (Exception e) {                e.printStackTrace();            }        } }

Field注解实现

1、定义注解

@Target(ElementType.FIELD)@Retention(RetentionPolicy.RUNTIME)public @interface ViewInject {    int value();}

2、实现注解

private static void injectView(Activity activity) {        Class<? extends Activity> clazz = activity.getClass();        //获得activity的所有成员变量        Field[] fields = clazz.getDeclaredFields();        for (Field field : fields) {        //获得每个成员变量上面的ViewInject注解，没有的话，就会返回null            ViewInject viewInject = field.getAnnotation(ViewInject.class);            if (viewInject != null) {                int viewId = viewInject.value();                View view = activity.findViewById(viewId);                try {                    field.setAccessible(true);                    field.set(activity, view);                } catch (IllegalAccessException e) {                    e.printStackTrace();                }            }        }    }

接口（方法）注解实现

1、定义注解

@Target(ElementType.METHOD)@Retention(RetentionPolicy.RUNTIME)public @interface OnClick {    int[] value();}

2、实现注解

public class ViewInjectUtils {    public static void inject(Activity activity) {        injectContentView(activity);        injectView(activity);        injectEvent(activity);    }    private static void injectEvent(final Activity activity) {        Class<? extends Activity> clazz = activity.getClass();        Method[] methods = clazz.getDeclaredMethods();        for (final Method method2 : methods) {            OnClick click = method2.getAnnotation(OnClick.class);            if (click != null) {                int[] viewId = click.value();                method2.setAccessible(true);                Object listener = Proxy.newProxyInstance(View.OnClickListener.class.getClassLoader(),                        new Class[]{View.OnClickListener.class}, new InvocationHandler() {                            @Override                            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {                                return method2.invoke(activity, args);                            }                        });                try {                    for (int id : viewId) {                        View v = activity.findViewById(id);                        Method setClickListener = v.getClass().getMethod("setOnClickListener", View.OnClickListener.class);                        setClickListener.invoke(v, listener);                    }                } catch (Exception e) {                    e.printStackTrace();                }            }        }    }