How to use reflection and dynamic proxy to implement a View annotation binding library in Java

Use reflection combined with dynamic proxy to implement a View annotation binding library, which supports View and event binding. The code is concise, easy to use, and has strong scalability.

Supported functions

• ##@ContentView Binding layout instead of setContentView()

• @BindView Bind View instead of findViewById()

• @OnClick Bind click event instead of setOnClickListener()

• @OnLongClick Bind long press event instead of setOnLongClickListener()

Code

Annotation class

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

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

@Target(ElementType.ANNOTATION_TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface OnEvent {
    //订阅方式
    String setCommonListener();
    //事件源对象
    Class<?> commonListener();
}

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@OnEvent(setCommonListener = "setOnClickListener",
        commonListener = View.OnClickListener.class)
public @interface OnClick {
    int value();
}

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@OnEvent(setCommonListener = "setOnLongClickListener",
        commonListener = View.OnLongClickListener.class)
public @interface OnLongClick {
    int value();
}

Implementation class

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得到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();
        //获取到当前页年所有方法并遍历
        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 {
                    //由于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);
                    //使用动态代理监听回调
                    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();
                }
            }
        }
    }
}

Use

@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;
    }
}

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