让你的代码减少三倍!使用kotlin开发Android(五) 监听器

在前面的博客中,有一个栗子,是点击按钮转跳的监听器。

让你的代码量减少3倍!使用kotlin开发Android(四) kotlin bean背后的秘密

可以看到,不用再new一个OnClickListener了。实际上这种写法是lambda的一种简略模式,通常情况下匿名内部类可以以如下表现形式展示:

简单来说就是->左边为参数,右面为结果。其过程相当于

从以上栗子可以看出,lambda可以极大简化我们的代码。当左面参数没有使用到的时候,可以省略掉整个左半部分”view->”,就如同第一个代码片一样。

给RecyclerView加监听

在MainActivity里添加一个RecyclerView。并且新建一个适配器起名MainAdapter

像往常一样写一个RecyclerView的布局

### 注意这个适配器里使用的一些小技巧

1.with改变作用域,如果你有一大堆需要重复写的前缀,则可以使用with改变作用域。如:

可以改为


2.在头部导入

这样就可以免去万恶的findviewbyid


3.View.infalte()代替LayoutInfalter.form().infalte()
这个没啥好说的,省点代码而已~~


4.String模板输出,类似于C语言的print

添加监听器

大家都知道,有个简便的方法就是直接给itemView添加个OnClickListener()~

所以在onBindViewHolder()开刀,注意写法,这里与java有不同

其中给了一个函数变量mListener, 他的输入为int,返回值为Unit(kotlin的null,不过是个具体的对象)

接下来给个set函数

这样就完成了item监听器的编写,所以我们的Activity代码如下:

本文这就结束了(嫌文字太短?不要急啦,先去动手实践下咯。。系列文章,既然挖了坑,就不会拖更的(吧..))

欢迎加入Kotlin小乐园群(这是一个高质量、优秀的圈子):479109923

如果你是Android开发者,那么你还可以来 wing的酒馆:425983695来分享你的开发经验哦

 

本项目使用的代码地址

35 thoughts on “让你的代码减少三倍!使用kotlin开发Android(五) 监听器

  1. var mListener: ((pos: Int) -> Unit)? = null

    fun setOnItemClickListener(listener: ((pos: Int) -> Unit)){
    mListener = listener
    } 请分析一下 ((pos: Int) -> Unit) 这是个什么类型

  2. adapter.setOnItemClickListener { pos->toast(“$pos”) }
    activity里面的这个代码 pos->toast(“$pos”) } 这个参数 pos怎么来的啊

      1. 这不叫回调把,就是把adatpter的监听器初始化为pos->toast(“$pos”) ,然后当你点击adapter里面item,会调用该监听器的执行方法。
        回调的意思A调用B的方法,然后在B的方法中又调用了A的方法,此时才叫回调。

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  13. listener: ((pos: Int) -> Unit)
    大神这个看不懂啊,能否详细解释一下,我觉得整篇文章就在这里

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