尝试访问Kotlin片段中的视图时发生NullPointerException [英] NullPointerException when trying to access views in a Kotlin fragment

问题描述

如何在Fragment s上使用Kotlin Android扩展? 如果在onCreateView()中使用它们，则会出现此NullPointerException异常:

How to use Kotlin Android Extensions with Fragments? If I use them inside onCreateView(), I get this NullPointerException exception:

由于:java.lang.NullPointerException:尝试调用虚拟 方法'android.view.View android.view.View.findViewById(int)'在 空对象引用

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference

这是片段代码:

package com.obaied.testrun.Fragment

import android.os.Bundle
import android.support.v4.app.Fragment
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import com.obaied.acaan.R
import kotlinx.android.synthetic.main.fragment_card_selector.*

public class CardSelectorFragment : Fragment() {
    val TAG = javaClass.canonicalName

    companion object {
        fun newInstance(): CardSelectorFragment {
            return CardSelectorFragment()
        }
    }

    override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        var rootView = inflater?.inflate(R.layout.fragment_card_selector, container, false)
        btn_K.setOnClickListener { Log.d(TAG, "onViewCreated(): hello world"); }

        return rootView
    }
}
`

推荐答案

科特林合成属性不是魔术，而是以非常简单的方式起作用的.当您访问btn_K时，它会调用getView().findViewById(R.id.btn_K).

Kotlin synthetic properties are not magic and work in a very simple way. When you access btn_K, it calls for getView().findViewById(R.id.btn_K).

问题是您访问它的时间太早. getView()返回onCreateView中的null.尝试使用onViewCreated方法:

The problem is that you are accessing it too soon. getView() returns null in onCreateView. Try doing it in the onViewCreated method:

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    btn_K.setOnClickListener { Log.d(TAG, "onViewCreated(): hello world"); }
}

这篇关于尝试访问Kotlin片段中的视图时发生NullPointerException的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！