Kotlin：设置TextView时lateinit属性未初始化

Question

我正在尝试在片段中设置TextView 的文本。我正在从我的 Pager Adapter 中的 Fragment 类调用一个方法来完成此操作，但这样做时收到以下错误：

Caused by: kotlin.UninitializedPropertyAccessException: lateinit property totalMsg has not been initialized

换句话说，似乎onCreateView 方法被触发 setTotalMessages 被调用： 下面是我的 TotalFragment 类的 Kotlin 代码：

class TotalFragment : Fragment() {
    lateinit var inf:View;
    lateinit var totalMsg:TextView;

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        inf = inflater!!.inflate(R.layout.total_fragment, container, false) as View;
        totalMsg = inf.findViewById(R.id.chat_count)
        Log.i("App", "done")
        return inf;
    }

    // Setter method that sets the text of the total messages #
    fun setTotalMessages(messageCount: String) : Unit {
        Log.i("App", "done2")
        totalMsg.text = "total # of messages exchanged: " + messageCount;
        //totalMessages.setText("total # of messages exchanged: " + messageCount);
    }
}

以下是我的寻呼机适配器代码：

class PageAdapter(private val myContext: Context, fm: FragmentManager, internal var totalTabs: Int) : FragmentPagerAdapter(fm) {
    // keep track of the fragment containing the cumulative statistics
    var totalFrag:TotalFragment = TotalFragment();

    // this is for fragment tabs
    override fun getItem(position: Int): Fragment? {
        when (position) {
            0 -> {
                return totalFrag
            }
            1 -> {
                return IndividualFragment()
            }
            2 -> {
                // val movieFragment = MovieFragment()
                return UsageFragment()
            }
            else -> return null
        }
    }

    // set the text of the cumulative texts label
    fun setCumulativeTexts(messageCount:Int) {
        totalFrag.setTotalMessages(messageCount.toString());
    }

    // this counts total number of tabs
    override fun getCount(): Int {
        return totalTabs
    }
}  

下面是MainActivity.kt 的 Kotlin 代码，我在其中调用了设置累积文本的方法：

val adapter = PageAdapter(this, supportFragmentManager, tabLayout!!.tabCount)
adapter.setCumulativeTexts(5)

Answer 1

仅使用var 而不是lateinit var

var inf: View? = null
var totalMsg: TextView? = null
var messageCount: String? = null

然后像下面这样使用它

fun setTotalMessages(messageCount: String) : Unit { 
    //store count here
    this.messageCount = messageCount
    totalMsg?.text = "total # of messages exchanged: " + messageCount
}

然后在创建视图后尝试设置计数

override fun onCreateView( inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle? ): View? { 
    inf = inflater!!.inflate(R.layout.total_fragment, container, false) as View; 
    totalMsg = inf?.findViewById(R.id.chat_count) 

    // set it from here
    totalMsg?.text = "total # of messages exchanged: " + messageCount

    return inf; 
} 

Answer 2

你试过了吗？

val adapter = PageAdapter(this, supportFragmentManager, tabLayout!!.tabCount)
viewPager.setAdapter(adapter)
adapter.setCumulativeTexts(5)

您还可以从 R.layout.total_fragment 添加代码以更好地理解问题吗？

Answer 3

onCreateView 在膨胀视图时被调用。您应该在onViewCreated 方法中获取对您的视图的引用（即在视图被膨胀之后）

override fun onViewCreated(...) {
    totalMsg = inf.findViewById(R.id.chat_count)
}