移動開發筆記（七） Fragment 手機和平板兼顧 簡易新聞應用

1.1動態添加Fragment

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
		button.setOnClickListener{
	replaceFragment(AnotherFragment())
	}
	replaceFragment(RightFragment())
    }

	private fun replaceFragment( fragment : Fragment){
	val fragmentManager = supportFragmentManager
	val transaction = fragmentManager.beginTransaction()
	transaction.replace(R.id.rightLayout,fragment)
	transaction.commit()

	}

}

1.2Fragment實現返回棧
transaction.addToBackStack(null)

...
	private fun replaceFragment( fragment : Fragment){
	val fragmentManager = supportFragmentManager
	val transaction = fragmentManager.beginTransaction()
	transaction.replace(R.id.rightLayout,fragment)
	transaction.addToBackStack(null)
	transaction.commit()

	}

1.3Fragment生命週期

1.運行狀態
2.暫停狀態
3.停止狀態
4.銷燬狀態
onAttach():當Fragment和Activity建立關聯時調用
onCreateView():爲Fragment創建視圖（加載佈局）時調用
onActivityCreated():確保與Fragment相關聯的Activity已經創建完畢時調用
onDestroyView():當與Fragment關聯的視圖被移除時調用
onDetach():當Fragment和Activity解除關係時調用

1.4使用限定符區別平板與手機端
在res目錄下創建layout-large文件夾,在文件夾內創建同名佈局

使用最小寬度限定符
在res目錄下創建layout-sw600dp文件夾,在文件夾內創建同名佈局
最小寬度限定符允許我們對屏幕的寬度制定一個最小值（以dp爲單位），以這個最小值爲臨界點。

2.實踐 一個簡易版的新聞應用

修改layout目錄下activity_main文件

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/newsTitleLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <fragment
        android:id="@+id/newsTitleFrag"
        android:name="com.example.fragmenttest.NewsTitleFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"></fragment>


</FrameLayout>

在layout-sw600dp目錄下創建activity_main文件

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <fragment
        android:id="@+id/newsTitleFrag"
        android:name="com.example.fragmenttest.NewsTitleFragment"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"></fragment>
    <FrameLayout
        android:id="@+id/newsContentLayout"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="3"
        >
        <fragment
            android:id="@+id/newsContentFrag"
            android:name="com.example.fragmenttest.NewsContentFragment"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            ></fragment>
    </FrameLayout>


</LinearLayout>

創建News實體類

class New (val title:String,val content:String){
}

創建news_title_fragment.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/newsTitleRecyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </androidx.recyclerview.widget.RecyclerView>
</LinearLayout>

創建news_title_frag.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/newsTitleRecyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </androidx.recyclerview.widget.RecyclerView>
</LinearLayout>

創建news_item.xml

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/newsTitle"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:maxLines="1"
    android:ellipsize="end"
    android:textSize="18sp"
    android:paddingLeft="10dp"
    android:paddingRight="10dp"
    android:paddingTop="15dp"
    android:paddingBottom="15dp">

</TextView>

創建NewsFragFragment 並在內部創建內部類NewsAdapter

class NewsTitleFragment :Fragment(){
    private var isTwoPane=false
    inner class NewsAdaapter(val newsList:List<New>):RecyclerView.Adapter<NewsAdaapter.ViewHolder>(){
        inner class ViewHolder(view:View) : RecyclerView.ViewHolder(view){
            val newsTitle : TextView=view.findViewById(R.id.newsTitle)
        }

        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
            val view =LayoutInflater.from(parent.context).inflate(R.layout.news_item,parent,false)
            val holder = ViewHolder(view)
            holder.itemView.setOnClickListener {
                val news = newsList[holder.adapterPosition]
                if(isTwoPane){
                    //如果是雙頁模式
                    val fragment=newsContentFrag as NewsContentFragment
                    fragment.refresh(news.title,news.content)
                }else{
                    //如果是單頁模式
                    NewsContentActivity.actionStart(parent.context,news.title,news.content)
                }
            }
            return holder
        }

        override fun onBindViewHolder(holder: ViewHolder, position: Int) {
            val news=newsList[position]
            holder.newsTitle.text=news.title
        }

        override fun getItemCount(): Int {
            return newsList.size
        }
    }
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.news_title_frag,container,false)
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        isTwoPane = activity?.findViewById<View>(R.id.newsContent) !=null
        val layoutManager=LinearLayoutManager(activity)
        newsTitleRecyclerView.layoutManager=layoutManager
        val adapter = NewsAdaapter(getNews())
        newsTitleRecyclerView.adapter=adapter
    }
    private fun getNews() : List<New>{
        val newsList=ArrayList<New>()
        for(i in 1..50){
            val news = New("這是新聞$i",getRandomLengthString("新聞$i 正在播報，看懂看不懂由你."))
            newsList.add(news)
        }
        return newsList
    }
    private fun getRandomLengthString(str:String) :String{
        val n=(1..20).random()
        val builder=StringBuilder()
        repeat(n){
            builder.append(str)
        }
        return builder.toString()
    }
}

創建news_content_frag.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <LinearLayout
        android:id="@+id/contentLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="invisible"
        android:orientation="vertical">
        <TextView
            android:id="@+id/newsTitle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:padding="10dp"
            android:textSize="20sp"
            ></TextView>
        <View
            android:layout_width="match_parent"
            android:layout_height="1dp"
            android:background="#000"
            ></View>
        <TextView
            android:id="@+id/newsContent"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:padding="15dp"
            android:textSize="18sp"
            ></TextView>
    </LinearLayout>
    <View
        android:layout_width="1dp"
        android:layout_height="match_parent"
        android:layout_alignParentLeft="true"
        android:background="#000"
        ></View>
</RelativeLayout>

創建NewsContentFragment

class NewsContentFragment : Fragment(){
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.new_content_frag,container,false)
    }
    fun refresh(title : String,content : String){
        contentLayout.visibility = View.VISIBLE
        newsTitle.text=title
        newsContent.text=content
    }

}

創建NewsContentActivity

class NewsContentActivity : AppCompatActivity() {
    companion object{
        fun actionStart(context : Context,title:String,content:String){
            val intent = Intent(context,NewsContentActivity::class.java).apply {
                putExtra("news_title",title)
                putExtra("news_content",content)
            }
            context.startActivity(intent)
        }
    }
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_news_content)
        val title =intent.getStringExtra("news_title")
        val content=intent.getStringExtra("news_content")
        if(title!=null &&content !=null){
            val fragment =newsContentFrag as NewsContentFragment
            fragment.refresh(title,content)
        }
    }
}

3.Kotlin擴充

3.1擴展函數
模板:fun ClassName.methodName(param1 : Int , param2 : Int) : Int { }

	fun String.lettersCount ( ) : Int {
	var count = 0
	for(char in this){
		if(char.isLetter()){
			count++
			}
	}
}

定義好可以直接這樣使用

val count = "ABC123xyz^%#"

3.2運算符重載
關鍵字:operator
模板：

class Obj{
	
	operator fun plus(pbj : Obj) :Obj{
	//處理相加邏輯
		}


}

之後可以這樣直接用

val obj1=Obj()
val obj2=Obj()
val obj3=obj1+obj2

比如Money類，錢是可以相加的這樣設計