Kotlin在android.support.v4.app.Fragment null对象引用中直接访问Button

Question

我试图直接访问片段中的按钮(android.support.v4),这就是它抛出的内容:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at             
com.....fragments.HomeFragment._$_findCachedViewById(HomeFragment.kt)
at 
com.....fragments.HomeFragment.onCreateView(HomeFragment.kt:25)

这是我试图在fragment_home.xml中访问的按钮:

<Button
    android:id="@+id/batteryInstallationButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/battery_installation"
    android:layout_weight="1"
    android:textSize="12sp"
    android:background="@drawable/custom_button"
    android:textColor="@color/white"
    android:layout_marginStart="5dp"
    android:layout_marginEnd="5dp"/>

这是HomeFragment.kt中的Kotlin代码

import android.content.Context
import android.net.Uri
import android.os.Bundle
import android.support.v4.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Toast

import kotlinx.android.synthetic.main.fragment_home.*

class HomeFragment : Fragment() {

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
}

override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,
                          savedInstanceState: Bundle?): View? {
    val rootView = inflater!!.inflate(R.layout.fragment_home, container, false)

    batteryInstallationButton?.setOnClickListener {
        Toast.makeText(context, "ehere", Toast.LENGTH_SHORT).show();
    }

    return rootView
}

companion object {

    fun newInstance(): HomeFragment {
        val fragment = HomeFragment()
        return fragment
    }
}

}

任何人都知道为什么我无法直接访问Button？

Answer 1

这里有两个选择:

1. batteryInstallationButton从onActivityCreated视图已经膨胀的位置进行访问,它将找到按钮.

2. 使用:

import kotlinx.android.synthetic.main.fragment_home.view.*

看到.view我添加到合成中并直接从已经膨胀的视图中使用它:

val rootView = inflater!!.inflate(R.layout.fragment_home, container, false)

rootView.batteryInstallationButton?.setOnClickListener.....

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