我试图制作一个RecyclerView,它将进入我片段的两个页面之一。这些页面放在NavigationDrawer活动中。目标是创建类似Play商店应用主页的内容。
但是我在运行时的代码片段中发现了一个错误。它说:
java.lang.IllegalStateException: mainMenu must not be null
at com.example.MyApp.app.fragment.MainFragment.onCreate(MainFragment.kt:49)
我一直在寻找一些SO线程,他们说布局没有正确加载。这导致一些元素没有被链接起来。另一位在评论中说,问题在于上下文未正确初始化。对我来说情况并非如此(相反,它是RecyclerView)。
以下是链接,希望它们可以作为参考。
在对我的代码进行多次检查后,我发誓我已将正确的布局放入。编辑:我导入了 kotlinx.android.synthetic.main.^
包,我把这个标志放在:^ $ {layout}。这是我的一些文件(如果这个帖子太长,请原谅我):
MainActivity.kt : AppCompatActivity()
^ activity_main。*
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// preparing the app bars
setSupportActionBar(toolBar)
// getting ready for the pages
val pagerAdapter = MainPagerAdapter(
supportFragmentManager,
resources.getString(R.string.tab_main),
resources.getString(R.string.tab_chat)
)
pager.adapter = pagerAdapter
// activating tabs
tabLayout.setupWithViewPager(pager)
val toggle = ActionBarDrawerToggle(
this, mainDrawer, toolbar,
R.string.navigation_drawer_open,
R.string.navigation_drawer_close)
mainDrawer.addDrawerListener(toggle)
navView.setNavigationItemSelectedListener(this)
toggle.syncState()
}
MainPagerAdapter.kt (fm: FragmentManager, private val page1: String, private val page2: String): FragmentPagerAdapter(fm)
override fun getItem(position: Int): Fragment? {
return when (position) {
0 -> MainFragment()
1 -> ChatFragment()
else -> null
}
}
override fun getCount() = 2
override fun getPageTitle(position: Int): CharSequence? {
return when (position) {
0 -> page1
1 -> page2
else -> null
}
}
MainFragment.kt : Fragment()
^ content_main。*
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?)
: View? = inflater.inflate(R.layout.content_main, container)
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
// this is the error
mainMenu.layoutManager = LinearLayoutManager(this.context)
mainMenu.adapter = MyAdapter(itemList) {
toast("${it.name} selected")
}
}
MyAdapter.kt: RecyclerView.Adapter<MyAdapter.MyHolder>()
^ item_custom.view。* (由Antonio Leiva提供)
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int)
= GoodsHolder(parent.inflate(R.layout.item_custom))
override fun getItemCount()
= itemList.size
override fun onBindViewHolder(holder: MyHolder, position: Int)
= holder.bind(itemList[position], listener)
class MyHolder(v: View): RecyclerView.ViewHolder(v){
private val item: Item? = null
private val view = v
fun bind(item: Item, listener: (Item) -> Unit)
= with (itemView) {
imgPic.setImageResource(item.pictureId)
txtName.text = item.name
txtPrice.text = item.price.toString()
setOnClickListener { listener(item) }
}
}
content_main.xml
<android.support.constraint.ConstraintLayout
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"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="com.example.MyApp.app.activity.MainActivity"
>
<!-- the RecyclerView that caused the runtime error -->
<android.support.v7.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/mainMenu"/>
</android.support.constraint.ConstraintLayout>
item_custom.xml(这些代码位于CardView内的LinearLayout内)
<ImageView
android:id="@+id/imgPic"
android:layout_width="match_parent"
android:layout_height="128dp"
app:srcCompat="@drawable/ic_menu_gallery" />
<TextView
android:id="@+id/txtName"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Get it while it's hot!"
android:layout_margin="@dimen/margin_small"
android:layout_marginTop="@dimen/margin_medium"
android:maxLines="2"
android:ellipsize="end"
android:textStyle="bold"
/>
<TextView
android:id="@+id/txtPrice"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="$3.000.000"
android:layout_marginLeft="@dimen/margin_small"
android:layout_marginStart="@dimen/margin_small"
android:layout_marginRight="@dimen/margin_small"
android:layout_marginEnd="@dimen/margin_small"
android:layout_marginBottom="@dimen/margin_medium"/>
ChatFragment.kt:Fragment()(仅包含onCreateView inflating content_main_chat.xml)
content_main_chat.xml(仅包含TextView)
答案 0 :(得分:5)
您尚未在MainFragment.kt
文件中初始化RecyclerView。你必须在下面的行之前初始化它:
mainMenu.layoutManager = LinearLayoutManager(this.context)
您可以通过以下行初始化RecyclerView:
var mainMenu = findViewById(R.id.mainMenu) as RecyclerView
您必须根据需要进行更改。
答案 1 :(得分:3)
对于那些遵循@Avijit Karmakar精采线索的人,请多加讨论,(RecyclerView error: No adapter attached; skipping layout) 我必须包括:
class WikiFragment : Fragment() {
val paginas: ArrayList<String> = ArrayList()
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
var listItems : View = inflater.inflate(R.layout.fragment_wiki, container, false)
var rv_frag_wiki = listItems.findViewById<View>(R.id.rv_frag_wiki) as RecyclerView
rv_frag_wiki.layoutManager = LinearLayoutManager(this.context)
rv_frag_wiki.adapter = PaginasAdapter(paginas, this.context)
return listItems
答案 2 :(得分:0)
您忘记初始化mainMenu
onCreate
内的MainFragment.kt
答案 3 :(得分:0)
设置recyclerView的layoutManager
mainMenu.layoutManager = LinearLayoutManager(this.context)
此状态您的recyclerView尚未初始化,因此您必须明确初始化recyclerView
val mainMenu = view.findViewById(R.id.recyclerView) as RecyclerView
答案 4 :(得分:0)
我认为初始化onViewCreated中的元素是一种更好的方法,例如@Egor Neliuba所讲授的: NullPointerException when trying to access views in a Kotlin fragment
答案 5 :(得分:0)
如果您正在使用片段:1.使用一个全局变量来保存布局参考
internal var root: View? = null // create a global variable which will hold your layout override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
root = inflater.inflate(R.layout.your_layout_file_name, container, false) // initialize it here
return root
}
要使用布局内部的任何视图,可以将其与(root。)一起使用:
root!!.recyclerView.layoutManager = LinearLayoutManager(context,LinearLayoutManager.VERTICAL, false)
答案 6 :(得分:0)
由于您使用的是Kotlin,因此无需使用var rv_frag_wiki = listItems.findViewById<View>(R.id.rv_frag_wiki) as RecyclerView
通过插件导入合成 第1步:
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
第2步:
在MainFragment中导入音色
import kotlinx.android.synthetic.main.content_menu.*
//
第3步:
最后进入MainFragment
在此处移动recyclerView的代码
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
rvList.layoutManager = LinearLayoutManager(context,
LinearLayoutManager.VERTICAL, false)
rvList.adapter = academyAdapter
}
答案 7 :(得分:0)
= note: expected `&mut TimerQueue`
found `&mut TimerQueue`
以下链接在我的情况下有效。