8.kotlin安卓实践课程-用kotlin写第一个fragment

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简介

主要会通过安卓实战来讲解kotlin语法和实际应用，本教程设及知识点包括框架模式mvp+mvvm, Databinding(数据绑定框架),Dagger2(依赖注入框架)，DeepLink（页面路由框架），Rxjava,RxAndroid(异步操作框架)，Retrofit,Okhtttp等，不过本教程重点在kotlin所以这些框架需要了解可自行百度。

针对人群：Android中级以上，kotlin入门

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我们马上开始完成第一个kotlin代码实现的fragment

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首先先看一下代码

/** * * Created by bigman on 18-05-18. */ class AndroidFragment : BaseBingingFragment<ViewRecyclerBinding>(), AndroidContract.View { private var mList = ArrayList<AndroidBean>() private lateinit var mAdapter: AndroidAdapter private var mPage = 1 @Inject lateinit var mPresenter: AndroidPresenter override fun createDataBinding(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): ViewRecyclerBinding { return ViewRecyclerBinding.inflate(inflater!!, container, false) } override fun initView() { mAdapter = AndroidAdapter(mList) context.getMainComponent().plus(AndroidModule(this)).inject(this) with(mBinding) { recyclerView.adapter = mAdapter recyclerView.layoutManager = LinearLayoutManager(context) recyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() { override fun onScrolled(recyclerView: RecyclerView?, dx: Int, dy: Int) { super.onScrolled(recyclerView, dx, dy) //是否滚动到底部 if (!recyclerView?.canScrollVertically(1)!!) { mPresenter.getData(++mPage, ANDROID) } } override fun onScrollStateChanged(recyclerView: RecyclerView?, newState: Int) { super.onScrollStateChanged(recyclerView, newState) } }) } //请求数据 mPresenter.getData(mPage, ANDROID) mAdapter.setOnItemClickListener { pos -> val url = URLEncoder.encode(mList[pos].url) GankRouter.router(context, GankClientUri.DETAIL + url) } } override fun setData(results: List<AndroidBean>) { mList.addAll(results) mAdapter.notifyDataSetChanged() } override fun onDestroy() { super.onDestroy() mPresenter.unSubscribe() } companion object { val ANDROID = "ANDROID" fun newInstance(): AndroidFragment { val fragment = AndroidFragment() val bundle = Bundle() fragment.arguments = bundle return fragment } } } 

AndroidFragment 代码结构其实和MainActivity的差不多，首先是两个主要方法createDataBinding和initView,他同样是基类声明的两个抽象方法，我们看看基类 BaseBingingFragment的代码：

/** * Created by bigman on 18-05-17. */ abstract class BaseBingingFragment<B:ViewDataBinding> : Fragment(){ lateinit var mBinding : B override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View { mBinding = createDataBinding(inflater,container,savedInstanceState) initView() return mBinding.root } override fun onViewCreated(view: View?, savedInstanceState: Bundle?) { super.onViewCreated(view, savedInstanceState) } abstract fun createDataBinding(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): B abstract fun initView() } 

当然它的实现和activity的基类一样，就是实现了databinding框架的页面绑定，不记得的同学可以翻看一下前面，我们再看基类提供的抽象方法的具体实现

override fun createDataBinding(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): ViewRecyclerBinding { return ViewRecyclerBinding.inflate(inflater!!, container, false) } 

这里就是把view_recycler.xml由Databinding自动生成类ViewRecyclerBinding和页面绑定起来

然后再看看initView方法实现代码

 override fun initView() { mAdapter = AndroidAdapter(mList) context.getMainComponent().plus(AndroidModule(this)).inject(this) with(mBinding) { recyclerView.adapter = mAdapter recyclerView.layoutManager = LinearLayoutManager(context) recyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() { override fun onScrolled(recyclerView: RecyclerView?, dx: Int, dy: Int) { super.onScrolled(recyclerView, dx, dy) //是否滚动到底部 if (!recyclerView?.canScrollVertically(1)!!) { mPresenter.getData(++mPage, ANDROID) } } override fun onScrollStateChanged(recyclerView: RecyclerView?, newState: Int) { super.onScrollStateChanged(recyclerView, newState) } }) } //请求数据 mPresenter.getData(mPage, ANDROID) mAdapter.setOnItemClickListener { pos -> val url = URLEncoder.encode(mList[pos].url) GankRouter.router(context, GankClientUri.DETAIL + url) } } 

首先是实例化了一个adapter适配器，然后把通过context.getMainComponent().plus(AndroidModule(this)).inject(this)实现了依赖注入，然后是通过一个with函数包含的代码块实现了 recyclerView的初始化和滚动监听

语法点: with函数

• with函数是将某对象作为函数的参数，在函数块内可以通过 this 指代该对象。返回值为函数块的最后一行或指定return表达式。
• 意思就是说如果要操作with的对象参数直接调用就行，不用多余的修饰符，比如这里的recyclerView就是mBinding对象的成员变量，完整写法应该是mBinding . recyclerView

剩下的需要注意这段代码

 companion object { val ANDROID = "ANDROID" fun newInstance(): AndroidFragment { val fragment = AndroidFragment() val bundle = Bundle() fragment.arguments = bundle return fragment } } 

这个伴生对象我们前面说过，这里再说一次，它相当于java的静态成员变量，这里的代码大家可以对比一下java的写法，相信java的写法大家都很熟悉了

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