小贝子编程

删除 kotlin 中的项目后，如何在 android 中更新回收视图?



我创建了一个回收视图，并在其中使用项目的卡片视图。每当我单击该按钮时，卡片视图中都有一个删除按钮，我的项目就会从 SQLite 数据库中删除。但要将其反映在 UI 上，应用需要重新启动。如何通知管理员项目已删除？

activity_main.xml

<?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">
<com.google.android.material.floatingactionbutton.FloatingActionButton
android:layout_width="57dp"
android:layout_height="64dp"
android:layout_marginEnd="40dp"
android:layout_marginBottom="40dp"
android:clickable="true"
android:onClick="addNewCredentials"
app:backgroundTint="#270867"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:srcCompat="@android:drawable/ic_menu_add" />
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginStart="1dp"
android:layout_marginTop="1dp"
android:layout_marginEnd="1dp"
android:layout_marginBottom="1dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="1.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0" >
</androidx.recyclerview.widget.RecyclerView>
</androidx.constraintlayout.widget.ConstraintLayout>

list_item_layout.xml

<?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:orientation="vertical" android:layout_width="match_parent"
android:layout_height="wrap_content">
<androidx.cardview.widget.CardView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="5dp">
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:id="@+id/urlView"
android:layout_width="300dp"
android:layout_height="30dp"
android:layout_marginTop="16dp"
android:layout_marginBottom="16dp"
android:text="url"
android:textAppearance="@style/TextAppearance.AppCompat.Large"
android:textSize="24sp"
android:textStyle="bold"
app:layout_constraintBottom_toTopOf="@+id/userNameView"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.1"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="1.0" />
<TextView
android:id="@+id/userNameView"
android:layout_width="300dp"
android:layout_height="25dp"
android:layout_marginBottom="16dp"
android:text="userName"
app:layout_constraintBottom_toTopOf="@+id/passwordView"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.1"
app:layout_constraintStart_toStartOf="parent" />
<TextView
android:id="@+id/passwordView"
android:layout_width="300dp"
android:layout_height="25dp"
android:layout_marginBottom="16dp"
android:text="password"
app:layout_constraintBottom_toTopOf="@+id/noteView"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.1"
app:layout_constraintStart_toStartOf="parent" />
<TextView
android:id="@+id/noteView"
android:layout_width="300dp"
android:layout_height="30dp"
android:layout_marginBottom="16dp"
android:text="note"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.1"
app:layout_constraintStart_toStartOf="parent" />
<Button
android:id="@+id/delButton"
android:layout_width="78dp"
android:layout_height="40dp"
android:layout_marginEnd="8dp"
android:layout_marginBottom="36dp"
android:background="#E6360F"
android:text="@string/delete_credential_button"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.cardview.widget.CardView>
</LinearLayout>

MainActivity.kt

package com.example.passwordmanager
import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Toast
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val recyclerView = findViewById<RecyclerView>(R.id.recyclerView)
recyclerView.layoutManager = LinearLayoutManager(this, RecyclerView.VERTICAL,false)
val db = DataBaseHandler(this)
val detailsData = db.readCredentials()
val adapter = CredentialAdapter(detailsData,this,{credentialsModel: CredentialsModel->deleteClick(credentialsModel)})
recyclerView.adapter = adapter
}
fun deleteClick(credential: CredentialsModel){
val db = DataBaseHandler(this)
if(db.deleteData(credential.id)){
//adapter.notifyItemRemoved(position)
Toast.makeText(applicationContext,"Deleted", Toast.LENGTH_SHORT).show()
}
}
fun addNewCredentials(view : View){
print("hello world")
val intent = Intent(this, AddDetailActivity::class.java)
intent.flags = Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK
startActivity(intent)
}
}

CredentialAdapter.kt

package com.example.passwordmanager
import android.content.Context
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import kotlinx.android.synthetic.main.list_item_layout.view.*
class CredentialAdapter(
private val items: List<CredentialsModel>,
ctx: Context, val clickListener: (CredentialsModel) -> Unit
): RecyclerView.Adapter<CredentialAdapter.ViewHolder>() {
var context = ctx
class ViewHolder(itemView: View):RecyclerView.ViewHolder(itemView){
fun bind(credential: CredentialsModel,clickListener: (CredentialsModel) -> Unit){
itemView.urlView.text = credential.url
itemView.userNameView.text = credential.userName
itemView.passwordView.text = credential.password
itemView.noteView.text = credential.note
itemView.delButton.setOnClickListener{clickListener(credential)}
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
return ViewHolder(LayoutInflater.from(parent.context).inflate(R.layout.list_item_layout,parent,false))
}
override fun getItemCount(): Int {
return items.size
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val credential:CredentialsModel = items[position]
holder.bind(credential,clickListener)
}
}

在onBindViewHolder中添加remove setOnClickListener。

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
holder.remove.setOnClickListener {
val db = DataBaseHandler(this)
if(db.deleteData(credential.id)){
notifyItemRemoved(holder.getAdapterPosition())
}
}
}

处理这些情况的最佳方法是使用 LiveData。 LiveData 基本上是一个可观察的类，它仅在发生更改时才读取数据。 您可以做的是在适配器中创建一个 set 函数，例如：

internal fun setData(data: List<Data>) {
this.data= dataList //this datalist is a list defined in your adapter 
notifyDataSetChanged()
}

现在，在您的主活动/片段中，在 onCreate 函数之外创建一个实时数据列表，如下所示：

private lateinit var allData:LiveData<List<Data>>

现在在你的onCreate函数中，use可以观察实时数据并为回收器视图设置数据，如下所示：

allData.observe(this, Observer { data->
data?.let { adapter.setData(it) }
})

您正在从数据库中删除该项目，但不是从回收器视图适配器内的列表中删除。

class CredentialAdapter(
private val items: ArrayList<CredentialsModel>, // Change list to arraylist
ctx: Context, val clickListener: (CredentialsModel, Int) -> Unit
): RecyclerView.Adapter<CredentialAdapter.ViewHolder>() {
...
...
fun remove(position: Int) {
// Remove and notify the adapter to reload
items.removeAt(position)
notifyItemRemoved(position)
}
class ViewHolder(itemView: View):RecyclerView.ViewHolder(itemView) {
fun bind(credential: CredentialsModel,clickListener: (CredentialsModel, Int) -> Unit){
...
...
// Pass adapter item position so that we can update the list after delete
itemView.delButton.setOnClickListener{clickListener(credential, adapterPosition)
}
} 
...
...
}

Inside MainActivity.kt

fun deleteClick(credential: CredentialsModel, position: Int) {
val db = DataBaseHandler(this)
if(db.deleteData(credential.id)){
adapter.remove(position)
Toast.makeText(applicationContext,"Deleted", Toast.LENGTH_SHORT).show()
}
}

使用 ListAdpater

class AdapterMain(var onClickListener: (Int) -> Unit) :
ListAdapter<Note, AdapterMain.NoteViewHolder>(DIFFCALBACK) {

companion object DIFFCALBACK : DiffUtil.ItemCallback<Note>() {
override fun areItemsTheSame(oldItem: Note, newItem: Note): Boolean {
return oldItem.id == newItem.id
}
override fun areContentsTheSame(oldItem: Note, newItem: Note): Boolean {
return oldItem.title == newItem.title &&
oldItem.description == newItem.description &&
oldItem.priority == newItem.priority
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): NoteViewHolder {
val view = LayoutInflater.from(parent.context).inflate(R.layout.note_item, parent, false)
return NoteViewHolder(view)
}
override fun onBindViewHolder(holder: NoteViewHolder, position: Int) {
holder.txtTitle.text = getItem(position).title
holder.txtDesc.text = getItem(position).description
holder.txtPriority.text = getItem(position).priority.toString()
}

inner class NoteViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
var txtTitle: TextView = itemView.txt_title
var txtDesc: TextView = itemView.txt_desc
var txtPriority: TextView = itemView.txt_priority
init {
itemView.setOnClickListener { onClickListener(adapterPosition) }
}
}

fun getNoteAt(position: Int): Note {
return getItem(position)
}

}

您可以看到带有kotlin，recyclerView，MVVM和的简单NoteApp的完整代码。

class coba ： AppCompatActivity(( { 私人后期变量回收视图：回收器视图 private lateinit var datalis ：ArrayList 覆盖乐趣创建(保存实例状态：捆绑？({ super.onCreate(savedInstanceState( 设置内容视图(R.layout.activity_coba( recycleView = findViewById(R.id.rcycoba( datalis = ArrayList((

val dtnama = arrayOf(
"Danial Sanganus",
"Bijonia Skolin",
"Alianes Pertoli",
"Sivanian Pertici",
"Olehsan alausi"
)
for (i in dtnama.indices){
datalis.add(
dataCoba(
dtnama[i]
)
)
populateData()
}
}
private fun populateData(){
val linearManager = LinearLayoutManager(this)
linearManager.reverseLayout=true
linearManager.stackFromEnd=true
recycleView.layoutManager=linearManager
val adp =adpCoba(this,datalis)
recycleView.adapter=adp
}

}

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