Android Kotlin findViewById不能为null [英] Android Kotlin findViewById must not be null

问题描述

我们已经创建了一个自定义警报对话框，该对话框通过将其转换为Kotlin在Java项目中使用. java.lang.IllegalStateException:findViewById(R.id.btnYES)不能为空

We have created a custom alert dialog that was used in a Java project by converting it to Kotlin The error posted below java.lang.IllegalStateException: findViewById(R.id.btnYES) must not be null

错误原因使我们难以理解！我们查看了许多帖子，并尝试了一些没有结果的帖子. Activity结构如下:PageTwoActivity具有自己的XML文件，并带有两个按钮.自定义对话框具有自己的xml文件 这是PageTwoActivity代码.没有两个用于PageTwoActivity的按钮 没有名称冲突

The error source is eluding us ! We have looked at a number of posts and tried a few with no results. The Activity structure is as follows PageTwoActivity has its own XML file with two buttons attached. The custom dialog has its own xml file Here is the PageTwoActivity code. Without the two buttons for PageTwoActivity NO name conflicts

import android.app.Dialog
import android.content.Intent
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Button
import android.widget.EditText
import android.widget.Toast

class PageTwoActivity : AppCompatActivity() {
internal lateinit var btnBACK: Button
internal lateinit var btnDIALOG: Button

internal lateinit var btnYES: Button
internal lateinit var btnNO: Button
internal lateinit var etStudentName:EditText
var EnteredText: String = ""

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_page_two)

    btnBACK = findViewById(R.id.btnBACK)
    btnDIALOG = findViewById(R.id.btnDIALOG)

    btnYES = findViewById(R.id.btnYES)
    btnNO = findViewById(R.id.btnNO)
    etStudentName = findViewById(R.id.etStudentName)
    addListenerOnButtonBACK()
    addListenerOnButtonDIALOG()

    Toast.makeText(this@PageTwoActivity, "You are on Page Two", 
    Toast.LENGTH_LONG).show()

}// END onCreate

这是自定义对话框"的代码

Here is the code for the Custom Dialog

    private fun doCustom() {

    val openDialog = Dialog(this)
    openDialog.setContentView(R.layout.custom_dialog)
    //val btnYES = view!!.findViewById<Button>(R.id.btnYES)
    //val btnNO = openDialog.findViewById(R.id.btnNO)
    //val etStudentName = openDialog.findViewById(R.id.etStudentName)
    openDialog.setCancelable(false)


    btnYES.setOnClickListener(View.OnClickListener {
        EnteredText = etStudentName.getText().toString().trim({ it <= ' ' })
        if (EnteredText.isEmpty()) {
            Toast.makeText(applicationContext, "Enter Your Name\n\n OR Click 
     DECLINE", Toast.LENGTH_LONG).show()
            return@OnClickListener
        }
        Toast.makeText(applicationContext, "Registered $EnteredText", 
        Toast.LENGTH_SHORT).show()
        openDialog.dismiss()
    })

    btnNO.setOnClickListener(View.OnClickListener {
        EnteredText = ""
        val intent = Intent(this@PageTwoActivity, MainActivity::class.java)
        startActivity(intent)
        openDialog.dismiss()
    })
    openDialog.show()
}

自定义对话框的XML文件代码

The XML file code for the custom dialog

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="400dp"
android:layout_height="200dp"
android:background="@color/color_lightGray">

<TextView
    android:id="@+id/tvDAT"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="70dp"
    android:layout_marginTop="30dp"
    android:text="Enter First and Last Name"
    android:textColor="@color/color_Black"
    android:textSize="22sp"
    android:textStyle="bold" />

<EditText
    android:id="@+id/etStudentName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="20dp"
    android:layout_marginTop="80dp"
    android:ems="14"
    android:gravity="center"
    android:inputType="textPersonName"
    android:text=""
    android:textColor="@color/color_Black"
    android:textSize="20sp"
    android:textStyle="bold" />

<Button
    android:id="@+id/btnYES"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="250dp"
    android:layout_marginTop="120dp"
    android:background="@color/color_Transparent"
    android:text="TAKE QUIZ"
    android:textColor="@color/color_deepBlue"
    android:textSize="22sp"
    android:textStyle="bold" />

<Button
    android:id="@+id/btnNO"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="22dp"
    android:layout_marginTop="120dp"
    android:background="@color/color_Transparent"
    android:text="DECLINE"
    android:textColor="@color/color_deepBlue"
    android:textSize="22sp"
    android:textStyle="bold" />

   </RelativeLayout>

所以问题是我们如何解决错误? 我们应该夸大自定义对话框xml吗? 如您所见，我们试图将声明移到doCustom函数中////val btnYES = view !!.findViewById(R.id.btnYES) 该链接提供了建议，但我们不知道从哪里开始 LINK

So the question is how do we FIX the error? Should we be inflating the custom dialog xml? As you can see we tried to move the declaration to find the id into the doCustom function //val btnYES = view!!.findViewById(R.id.btnYES) this link offers advice but we have no idea where to start LINK

推荐答案

正如@Declan Nnadozie所述:btnYES = findViewById(R.id.btnYES)返回null，因为btnYES不是contentView内膨胀为PageTwoActivity的视图.
在对话框中突出显示的内容中可以找到按钮btnYES和btnNO和EditText etStudentName:
同样在Kotlin中，您不需要findViewById即可访问活动的视图.
您可以删除所有这些内容:

As @Declan Nnadozie already mentioned: btnYES = findViewById(R.id.btnYES) returns null because btnYES is not a view inside the contentView inflated to PageTwoActivity.
The buttons btnYES and btnNO and the EditText etStudentName can be found in the content that is inflated in the dialog:
Also in Kotlin you do not need findViewById to access the activity's views.
You can delete all these:

internal lateinit var btnBACK: Button
internal lateinit var btnDIALOG: Button

internal lateinit var btnYES: Button
internal lateinit var btnNO: Button
internal lateinit var etStudentName:EditText

我的建议是使用以下代码:

My suggestion is to use the below code:

class PageTwoActivity : AppCompatActivity() {
var EnteredText: String = ""

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_page_two)

        addListenerOnButtonBACK()
        addListenerOnButtonDIALOG()

        Toast.makeText(this@PageTwoActivity, "You are on Page Two",
            Toast.LENGTH_LONG).show()
    }

    fun doCustom(v: View) {
        val openDialog = Dialog(this)
        openDialog.setContentView(R.layout.custom_dialog)
        val btnYES = openDialog.findViewById<Button>(R.id.btnYES)
        val btnNO = openDialog.findViewById<Button>(R.id.btnNO)
        val etStudentName = openDialog.findViewById<EditText>(R.id.etStudentName)
        openDialog.setCancelable(false)

        btnYES.setOnClickListener(View.OnClickListener {
            EnteredText = etStudentName.getText().toString().trim({ it <= ' ' })
            if (EnteredText.isEmpty()) {
                Toast.makeText(applicationContext, "Enter Your Name\n\n OR Click DECLINE", Toast.LENGTH_LONG).show()
                        return@OnClickListener
            }
            Toast.makeText(applicationContext, "Registered $EnteredText", Toast.LENGTH_SHORT).show()
            openDialog.dismiss()
        })

        btnNO.setOnClickListener(View.OnClickListener {
            EnteredText = ""
            val intent = Intent(this@PageTwoActivity, MainActivity::class.java)
            startActivity(intent)
            openDialog.dismiss()
        })
        openDialog.show()
    }

这篇关于Android Kotlin findViewById不能为null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！