dim.red

#背景
android 的中设置监听有两种.

  • 一种 setOnXXListener (eg View.setOncClickListener()) .
  • 一种 addOnXXXListener (TextView.addTextWatchListener());
    两种的区别是第一种内部只会保存一个listener, 每次调用就是覆盖.
    第二种内部会保存一个List, 每次调用的时候就是添加一个监听器.

定义

1
2
3
4
5
public interface OnStatusListener {
    void onChange();
    void onChange1();
    void onChange2();
}

优化前

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
public class StastusManager {

    private List<OnStatusListener> onStatusListeners = new ArrayList<>();

    public void addOnStastusListener(OnStatusListener onStatusListener) {
        onStatusListeners.add(onStatusListener);
    }

    public void removeOnStatusListener(OnStatusListener onStatusListener) {
        onStatusListeners.remove(onStatusListener);
    }

    public void onChange() {
        for (OnStatusListener onStatusListener : onStatusListeners) {
            onStatusListener.onChange();
        }
    }
    public void onChange1() {
        for (OnStatusListener onStatusListener : onStatusListeners) {
            onStatusListener.onChange1();
        }
    }
    public void onChange2() {
        for (OnStatusListener onStatusListener : onStatusListeners) {
            onStatusListener.onChange2();
        }
    }
}

当接口方法多了以后, 相似代码就变更多了.
我们使用动态代理 优化一下相似代码

优化后

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
public class StastusManager {

    private DynamicInterface<OnStatusListener> onStatusListeners = DynamicFactory.newObject(OnStatusListener.class);

    public void addOnStastusListener(OnStatusListener onStatusListener) {
        onStatusListeners.addT(onStatusListener);
    }

    public void removeOnStatusListener(OnStatusListener onStatusListener) {
        onStatusListeners.removeT(onStatusListener);
    }

    public void onChange() {
        onStatusListeners.castT().onChange();
    }

    public void onChange1() {
        onStatusListeners.castT().onChange1();
    }

    public void onChange2() {
        onStatusListeners.castT().onChange2();
    }
}

优化以后没有了 List 类和每次的 for 循环. 现在还不能感觉到这个方式的好处. 当你有大量的 addXXlistener 你会发现, 比起之前的方式. 这种更加的优雅.
下面是实现的关键代码

1
2
3
4
5
6
7
8
9
10
11
12
13
/**
 * Created by dim on 2017/12/16.
 */
@Keep
public interface DynamicInterface<T extends Object> {

    void addT(T t);

    void removeT(T t);

    T castT();

}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
/**
 * Created by dim on 2017/12/16.
 */

public class DynamicFactory {

    public static <T> DynamicInterface<T> newObject(final Class<T> cls) {

        if (!cls.isInterface()) {
            throw new IllegalArgumentException("API declarations must be interfaces.");
        }

        if (cls.getInterfaces().length > 0) {
            throw new IllegalArgumentException("API interfaces must not extend other interfaces.");
        }

        return (DynamicInterface<T>) Proxy.newProxyInstance(cls.getClassLoader(),
                new Class<?>[]{cls, DynamicInterface.class}, new InvocationHandler() {
                    private List<T> list = new ArrayList<>();

                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

                        if (method.getName().equals("addT") || method.getName().equals("removeT")) {
                            if (args != null && args.length == 1 && cls.isInstance(args[0])) {
                                if (method.getName().equals("addT")) {
                                    list.add((T) args[0]);
                                } else if (method.getName().equals("removeT")) {
                                    list.remove((T) args[0]);
                                }
                                return null;
                            }
                        }
                        if (method.getName().equals("castT") && args == null) {
                            return proxy;
                        }
                        Class<?> returnType = method.getReturnType();
                        if (returnType.isAssignableFrom(boolean.class)) {

                            boolean object = true;
                            for (T t : list) {
                                if (!(boolean) method.invoke(t, args)) {
                                    object = false;
                                }
                            }
                            return object;
                        } else if (returnType.isAssignableFrom(Boolean.class)) {
                            Boolean object = Boolean.TRUE;
                            Boolean temp;
                            for (T t : list) {
                                if ((temp = (Boolean) method.invoke(t, args)) != null && !temp) {
                                    object = Boolean.FALSE;
                                }
                            }
                            return object;
                        } else if (returnType.isAssignableFrom(Void.class) || returnType.isAssignableFrom(void.class)) {
                            for (T t : list) {
                                method.invoke(t, args);
                            }
                            return null;
                        } else {
                            throw new IllegalArgumentException("returnType must boolean Boolean Void void");
                        }
                    }
                });
    }
}