让你的代码减少三倍！使用kotlin开发Android(五) 监听器

wing％1 $ S

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

1
2
3
4
5
6
button.setOnClickListener {
val user = User("name")
user.id = "100"
SecondActivity.startActivity(this,user)
}
 

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：

1
2
3
4
button.setOnClickListener {
view-> toast(view.id.toString())
}
 

简单来说就是->左边为参数，右面为结果。其过程相当于

1
2
3
4
5
6
7
<br />button.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View view){
toast(view.id.toString())
}
})
 

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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
<br />import kotlinx.android.synthetic.main.item_main.view.*
 
class MainAdapter: RecyclerView.Adapter() {
override fun onBindViewHolder(holder: ViewHolder?, position: Int) {
 
//改变作用域，with{}都是属于itemView
with(holder?.itemView!!){
tv_content.text = "第 $position 条数据"
}
}
 
override fun getItemCount(): Int {
return 5
}
 
override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): ViewHolder {
return ViewHolder(View.inflate(parent?.context, R.layout.item_main,null))
}
class ViewHolder(itemView: View?) : RecyclerView.ViewHolder(itemView) {
 
}
}
 

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:

1
2
3
4
5
mBinding?.tvName?.text = "张三"
mBinding?.tvContent?.text = "张三跟李四有py交易"
mBinding?.ivIcon.resouce = R.drawable.icon
 
 

可以改为

1
2
3
4
5
6
with(mBinding){
tvName?.text = "张三"
tvContent?.text = "张三跟李四有py交易"
ivIcon.resouce = R.drawable.icon
}
 

2.在头部导入

1
2
import kotlinx.android.synthetic.main.item_main.view.*
 

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

1
2
3
4
5
6
7
8
9
10
11
12
13
class MainAdapter : RecyclerView.Adapter() {
var mListener: ((pos: Int) -> Unit)? = null
 
fun setOnItemClickListener(listener: ((pos: Int) -> Unit)){
mListener = listener
}
override fun onBindViewHolder(holder: ViewHolder?, position: Int) {
with(holder?.itemView!!) {
tv_content.text = "第 $position 条数据"
setOnClickListener { mListener?.invoke(position) }
}
}
 

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)

1
2
var mListener: ((pos: Int) -> Unit)? = null
 

接下来给个set函数

1
2
3
4
fun setOnItemClickListener(listener: ((pos: Int) -> Unit)){
mListener = listener
}
 

这样就完成了item监听器的编写，所以我们的Activity代码如下：

1
2
3
4
5
val adapter = MainAdapter()
recyclerView.adapter = adapter
recyclerView.layoutManager = LinearLayoutManager(this)
adapter.setOnItemClickListener { pos->toast("$pos") }
 

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

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

  2. 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

    回复

  3. 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

    回复

      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。

        回复

  6. However, you can find significant risks involved wheen you’re dealing with private funding sources mainly because that they’ll dictate your business very quickly.
    And ssuch documentation will allow that yoou gauge your
    organization’s standing around all times and help out with
    reporting and paying of the appropriate levels of vadious taxes.
    We bargained from time to time; we gave in maybe; and
    we cheated sometimes.

    回复

  7. This relates to aany business if they are global, national or community based.
    Yes, right now your orgfanization carries a little of your personality within it,
    which is ok. The skill of joining a team and together to realize goals is quite
    important.

    回复

  11. Whatever one does, don’t spend high costs on name brand baby clothes unless funds
    are not an object for you. The shoe seller can assess the local
    terrain and may then discuss special activities that produce the
    highlighted footwear so very beneficial. Durting those Urgent Shopping Trips:So you have to go
    from sttation for some time, or you require some urgent
    clothes for some reason, and apso you don’t have the budget that you’d lime to get,
    it’s perfectly fine tto acquire clothes which are
    inexpensive and affordable.

    回复

  12. The biggest concern of people today is not only feelinng buut alo
    looking very healthy. If you need to generate any adjustments, you will possess the required time to ake any ecessary changes.
    Keywords inmclude the first thing to do in brosing the world wide web
    as this is wuat mot online website does to make their business noticeable in public.

    回复

  13. How can you prottect neglect the as well as your child’s if somewhere down the road, tthe adult
    children separate or divorce. This is very true if you are looking in an item tbat is similar to the
    one you originally chose. Despite its nearness
    to bigger, noisier, and much more packed Patong, Karon has a lengthy stretch of quiet beachfront, and presents a lovely vjewpoint in the sunset.

    回复

  14. The traditional stilettos was suddenly passed over to the hot new and much more trendy
    kitten heels. It would seem that a little bit of UK fashion will make your wardrobe interesting and
    add an international flare. Once you have reliable information of shoes you
    prefer, you’ll be able to find your perfect pair.

    回复

  15. If you might be pear-shaped (with larger hips and
    legs) avoid any clothing thjat would emphasize those
    areas. Another crucial consideration will be tthe capital because without one there is no wayy that one could start your business.
    This will help you to acquire what you cann only afford
    so that you are left with the running capital.

    回复

  17. CostHelper – Realise what cost homeowners аге paying. You’ll diuscover otһer beneficial info.
    CostHelper ρlaces tһᥱsᥱ labbour pices in perspective.
    Ꮢesearch а large numƅer oof matters oon CostHelper.

    回复

  21. I have to thank you for the efforts you’ve put in writing this website.
    I’m hoping to see the same high-grade blog posts by you in the future as well.
    In truth, your creative writing abilities has inspired me
    to get my very own website now 😉

    回复

  23. Ηi, I think your website might be havіng browser
    compatibiⅼity issues. When I look at your blog site in Opera, it looks fine but when opening іn Internet Explorer,
    it has some overlapping. I just wanted to giѵe you
    a quick heads up! Other then that, superb
    blog!

    回复

  26. 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

    回复

  27. I’ve been exploring for a little bit for any high quality articles or weblog posts
    in this sort of area . Exploring in Yahoo I at last stumbled upon this
    site. Studying this information So i am happy to exhibit that I have a very excellent uncanny feeling I found
    out exactly what I needed. I so much without a doubt will make
    certain to don?t disregard this website and give it a
    look on a constant basis.

    回复

  29. Hiya very nice site!! Guy .. Excellent .. Wonderful ..
    I will bookmark your site and take the feeds also?
    I’m happy to seek out so many useful info here in the put up, we need work out extra
    strategies on this regard, thank you for sharing.
    . . . . .

    回复

  31. I do not comment, ƅut after Ƅrowsing through some of the remarks here 让你的代码减少三倍！使用kotlin开发Andгoid(五)
    监听器 – 大精-wing的地方酒馆.
    I actually do havе a few questions for ｙou іf it’s okay.

    Could it be simply me оr does it seem like a few of the comments come ɑϲrosѕ as іf they are written by brain dead people?
    😛 And, if you are writing at other social sites, I woսld like to follow you.

    Сould you list of the complete urlѕ of your sociаl
    networking pages like your twitter feed, Facebook page or linkedіn profile?

    回复

  33. I was honored to obtain a call from my friend as soon as he observed the important points
    shared on the site. Studying your blog post is a real amazing
    experience. Thanks again for thinking of
    readers at all like me, and I hope for you the best of achievements like
    a professional in this field.

    回复

  34. Tһanks for a marvеlous posting! I seriouѕly enjoyed reading it, you’re a great autһor.
    I will make sure to bookmark your bloɡ and definitely will come back somedaʏ.
    I want to encоurage yourself to continue your great work,
    have a nice afternoon!

    回复

  36. Hi, i think that i ѕaw you visited my ԝeb site thus
    i came to “return the favor”.I’m attempting to find things to improve
    my web ѕite!І suppose its ok to usе ɑ few of your ideas!!

    回复

  41. That is a really good tip particularly to those fresh to the blogosphere.
    Brief but very accurate information… Thank you for sharing this one.
    A must read post!
    STRIKEWIN

    回复

  43. There’s activities to keep everyone entertained, from the
    most experienced adventurers to those that like easier pursuits, and a good
    combination of getting muddy on jungle treks to sipping on your favorite cocktail
    during a sunset canoe ride.

    回复

  47. Thank you for every other informative web site. Where else could
    I get that kind of information written in such a perfect means?
    I’ve a challenge that I’m simply now operating on, and I have been at the glance out for such information.

    回复

  49. Hi there everyone, it’s my first pay a quick visit at this web site, and article is truly fruitful designed for me, keep
    up posting these types of articles.

    回复

  51. I think that everything typed made a ton of sense.
    However, what about this? suppose you added a little content?

    I am not saying your information is not good., but suppose you added a post title that makes people want
    more? I mean 让你的代码减少三倍！使用kotlin开发Android(五) 监听器 – 大精-wing的地方酒馆 is a little boring.
    You could glance at Yahoo’s home page and see how they write article titles to grab viewers interested.
    You might try adding a video or a pic or two to grab readers excited about everything’ve written. In my opinion, it might bring your website a little bit more
    interesting.

    回复

向free进行回复 取消回复

电子邮件地址不会被公开。