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;
}

}

正文完