一 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.

二 定义

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public interface OnStatusListener {
void onChange();
void onChange1();
void onChange2();
}

三 优化前

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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

四 优化后

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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

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/**
* Created by dim on 2017/12/16.
*/
@Keep
public interface DynamicInterface<T extends Object> {
void addT(T t);
void removeT(T t);
T castT();
}

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/**
* 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");
}
}
});
}
}