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(); } } } }