关于经验:2021助理高薪拉钩产品经理高薪训练营

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使用反射和动静代理实现一个View注解绑定库

反对的功能
@ContentView 绑定layout 代替setContentView()
@BindView 绑定View 代替findViewById()
@OnClick 绑定点击事件 代替setOnClickListener()
@OnLongClick 绑定长按事件 代替setOnLongClickListener()

代码
注解类
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface ContentView {

int value();

}
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@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface BindView {

int value();

}
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@Target(ElementType.ANNOTATION_TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface OnEvent {

//订阅形式
String setCommonListener();
//事件源对象
Class<?> commonListener();

}
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@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@OnEvent(setCommonListener = “setOnClickListener”,

    commonListener = View.OnClickListener.class)

public @interface OnClick {

int value();

}
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@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@OnEvent(setCommonListener = “setOnLongClickListener”,

    commonListener = View.OnLongClickListener.class)

public @interface OnLongClick {

int value();

}
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实现类
public class MsInjector {

public static void inject(Object object) {
    injectContentView(object);
    injectView(object);
    injectEvent(object);
}
private static void injectContentView(Object object) {
    Class<?> clazz = object.getClass();
    //获取到ContentView注解
    ContentView contentView = clazz.getAnnotation(ContentView.class);
    if (contentView == null) {
        return;
    }
    //获取到注解的值，也就是layoutResID
    int layoutResID = contentView.value();
    try {
        //反射出setContentView方法并调用
        Method method = clazz.getMethod("setContentView", int.class);
        method.invoke(object, layoutResID);
    } catch (Exception e) {
        e.printStackTrace();
    }
}
private static void injectView(Object object) {
    Class<?> clazz = object.getClass();
    //获取到所有字段并遍历
    Field[] fields = clazz.getDeclaredFields();
    for (Field field : fields) {
        field.setAccessible(true);
        //获取字段上的BindView注解
        BindView bindView = field.getAnnotation(BindView.class);
        if (bindView == null) {
            continue;
        }
        //获取到viewId
        int viewId = bindView.value();
        try {
            //通过反射调用findViewById失去view实例对象
            Method method = clazz.getMethod("findViewById", int.class);
            Object view = method.invoke(object, viewId);
            //赋值给注解标注的对应字段
            field.set(object, view);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
private static void injectEvent(Object object) {
    Class<?> clazz = object.getClass();
    //获取到当前页年一切办法并遍历
    Method[] declaredMethods = clazz.getDeclaredMethods();
    for (Method declaredMethod : declaredMethods) {
        declaredMethod.setAccessible(true);
        //获取方法上的所有注解并遍历
        Annotation[] annotations = declaredMethod.getDeclaredAnnotations();
        for (Annotation annotation : annotations) {
            //获取注解本身
            Class<? extends Annotation> annotationType = annotation.annotationType();
            //获取注解上的OnEvent注解
            OnEvent onEvent = annotationType.getAnnotation(OnEvent.class);
            if (onEvent == null) {
                continue;
            }
            //拿到注解中的元素
            String setCommonListener = onEvent.setCommonListener();
            Class<?> commonListener = onEvent.commonListener();
            try {
                //因为上边没有明确获取是哪个注解，所以这里需要使用反射获取viewId
                Method valueMethod = annotationType.getDeclaredMethod("value");
                valueMethod.setAccessible(true);
                int viewId = (int) valueMethod.invoke(annotation);
                //通过反射findViewById获取到对应的view
                Method findViewByIdMethod = clazz.getMethod("findViewById", int.class);
                Object view = findViewByIdMethod.invoke(object, viewId);
                //通过反射获取到view中对应的setCommonListener方法
                Method viewMethod = view.getClass().getMethod(setCommonListener, commonListener);
                //使用动静代理监听回调
                Object proxy = Proxy.newProxyInstance(
                        clazz.getClassLoader(),
                        new Class[]{commonListener},
                        new InvocationHandler() {
                            @Override
                            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                                //最终执行被标注的方法
                                return declaredMethod.invoke(object, null);
                            }
                        }
                );
                //调用view的setCommonListener方法
                viewMethod.invoke(view, proxy);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

}
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使用
@ContentView(R.layout.activity_main)
public class MainActivity extends AppCompatActivity {

@BindView(R.id.button1)
private Button button1;
@BindView(R.id.button2)
Button button2;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    MsInjector.inject(this);
}
@OnClick(R.id.button1)
public void clickButton1() {
    Toast.makeText(this, "click button1", Toast.LENGTH_SHORT).show();
}
@OnClick(R.id.button2)
public void clickButton2() {
    Toast.makeText(this, "click button2", Toast.LENGTH_SHORT).show();
}
@OnLongClick(R.id.button1)
public boolean longClickButton1() {
    Toast.makeText(this, "long click button1", Toast.LENGTH_SHORT).show();
    return false;
}
@OnLongClick(R.id.button2)
public boolean longClickButton2() {
    Toast.makeText(this, "long click button2", Toast.LENGTH_SHORT).show();
    return false;
}

}