我已经创建了回收者视图,我想保存待办事项。过程是:单击添加图标,然后显示另一个活动是TaskActivity,然后输入任务名称并单击保存按钮。下面的错误导致:java.lang.NullPointerException: findViewById(R.id.btnSave)必须不是null
我们已经看了一些帖子,并尝试了一些没有结果。
下面是MainActivity.kt 的代码package abc.com.recyclerviewuserinput
import android.app.Activity
import android.content.Context
import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Button
import android.widget.EditText
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
class MainActivity : AppCompatActivity() {
lateinit var recyclerMain : RecyclerView
lateinit var layoutmanger: RecyclerView.LayoutManager
lateinit var btnSave: Button
val myList = ArrayList<String>()
// declare variable for the adapter
lateinit var recyclerAdapter: Adapter // here Adapter is name of Adapter class
// lateinit var editTaskName : EditText
override fun onCreate(savedInstanceState: Bundle?) {
// val view= layoutInflater.inflate(R.layout.single_row, container, false )
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
recyclerAdapter = Adapter(this, myList) // recycle Adapter
recyclerMain= findViewById(R.id.recyclerMain) // Recycler view
layoutmanger= LinearLayoutManager(this) // layout manager
var editTaskName= findViewById <EditText>(R.id.editTaskName)
btnSave= findViewById(R.id.btnSave)
btnSave.setOnClickListener {
myList.add(editTaskName.text.toString() )
}
//Now set layoutmanager and recycler Adapter with Recycler view
recyclerMain.adapter= recyclerAdapter
recyclerMain.layoutManager= layoutmanger
}
fun openNewTask(view: View) {
startActivity(Intent(this,TaskActivity:: class.java))
}
}
下面是TaskActivity.kt
的代码package abc.com.recyclerviewuserinput
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import android.widget.EditText
class TaskActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_task)
}
}
下面是activity_task.xml
的代码<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
android:orientation="vertical"
tools:context=".TaskActivity">
<EditText
android:id="@+id/editTaskName"
android:layout_width="match_parent"
android:layout_height="50dp"
android:text="Pankaj"
android:hint="@string/enter_task_name_here"
android:inputType="textPersonName"
/>
<Button
android:id="@+id/btnSave"
android:layout_marginTop="40dp"
android:layout_width="match_parent"
android:layout_height="50dp"
android:textSize="20sp"
android:text="@string/add_to_task" />
</LinearLayout>
下面是activity_main.xml
的代码<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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"
tools:context=".MainActivity">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recyclerMain"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
<com.google.android.material.floatingactionbutton.FloatingActionButton
android:layout_width="wrap_content"
android:onClick="openNewTask"
android:tint="@color/purple_500"
android:layout_height="wrap_content"
android:layout_margin="23dp"
android:src="@drawable/add"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
tools:ignore="UsingOnClickInXml" />
</androidx.constraintlayout.widget.ConstraintLayout>
这是Adapter.kt
package abc.com.recyclerviewuserinput
import android.content.Context
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView
import org.w3c.dom.Text
class Adapter(val context: Context, val itemList : ArrayList<String>): RecyclerView.Adapter<Adapter.SampleViewHolder>() {
class SampleViewHolder (view: View): RecyclerView.ViewHolder(view)
{
val rowtextView: TextView= view.findViewById(R.id.txtRecyclerRowItem)
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): SampleViewHolder {
val view=LayoutInflater.from(parent.context).inflate(R.layout.single_row, parent,false)
return SampleViewHolder(view)
}
override fun onBindViewHolder(holder: SampleViewHolder, position: Int) {
val text= itemList[position]
holder.rowtextView.text= text
}
override fun getItemCount(): Int {
return itemList.size
}
}
为什么indViewById(R.id.btnSave)不能为空显示在这里。我也尝试过通过lateinit var声明,但他也显示错误。那么如何解决这个问题呢?
看起来btnsave是在activity_task.xml,但你试图在Mainactivity中使用它。
看看btnSave是从哪个活动导入的。理想情况下,最好不要在活动/片段之间重复id名。
欢呼兄弟,你不能在主活动中调用btnSave按钮,因为它不是在主活动上创建的。它在activity_task上创建。尝试创建一个扩展activity_task.xml的适配器,然后在onbindviewholder
中执行按钮操作