Kotlin中观察者模式

最新推荐文章于 2025-01-16 22:34:00 发布

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本文通过一个报社与读者的实例，展示了观察者模式在安卓GUI中的应用。当报社（被观察者）发布新闻时，所有订阅的读者（观察者）会收到更新通知，实现事件响应逻辑。

安卓中的GUI经常会用到观察者模式，当发生点击等事件时，就会处理一些逻辑，比如EventBus：

我写了一个简单的例子，报社发布新闻，读者获取新闻。

package MyObserver

// 被观察者
class Newspaper{

    private var title:String = ""
    private var text:String = ""
    private var readers = HashSet<Reader>()
    private var changed:Boolean = false

    public fun addReader(reader:Reader){
        readers.add(reader)
    }

    public fun deleteReader(reader: Reader){
        if(reader in readers){
            readers.remove(reader)
        }
    }

    private fun notifyReader(){
        if(changed){
            for(reader in readers){
                reader.update(title, text)
            }
        }
        changed = false
    }

    public fun set(title:String, text:String){
        this.title = title
        this.text = text
        changed = true
        notifyReader()
    }
}

package MyObserver

// 观察者
class Reader(val name:String) {
    private var title:String = ""
    private var text:String = ""

    public fun update(title:String, text:String){
        this.title = title
        this.text = text
    }

    public fun show(){
        println("name is $name, title is $title, text is $text")
    }
}

package MyObserver

fun main() {
    val reader1 = Reader("Jack")
    val reader2 = Reader("Rose")
    val newspaper = Newspaper();
    newspaper.addReader(reader1)
    newspaper.addReader(reader2)
    newspaper.set("星期一", "下雨了")
    reader1.show()
    reader2.show()
    newspaper.set("星期二", "热死了")
    reader1.show()
    reader2.show()
}

运行结果：