无法将数据插入 SQLite-Kotlin-Android

Question

我试着运行这段代码，一切都很好。我检查了每个变量。它获取并传递数据。该表是在我的数据库中创建的。运行后没有错误消息。当我点击插入按钮时，如果插入数据失败，它会给我(失败(，就像我编码的那样。桌子是空的！我什么都试过了，但没有成功！

package com.example.myapplication
class User{
var id:Int=0
var name:String=""
var age:Int=0
constructor(name:String, age:Int){
this.name=name
this.age=age}
constructor(){}
}

package com.example.myapplication
import android.content.ContentValues
import android.content.Context
import android.database.Cursor
import android.database.sqlite.SQLiteDatabase
import android.database.sqlite.SQLiteOpenHelper
import android.widget.Toast
val DATABASE_NAME="MyDB"
val TABLE_NAME="Users"
val COL_NAME="name"
val COL_AGE="age"
val COL_ID="id"
class DataBaseHandler(var context: Context):SQLiteOpenHelper(context, DATABASE_NAME,null,1) {
override fun onCreate(db: SQLiteDatabase?) {
val creatTable="CREATE TABLE "+ TABLE_NAME+" ("+
COL_ID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+
COL_NAME+" VARCHAR(256),"+
COL_AGE +" INTEGER)";
db?.execSQL(creatTable)
}
override fun onUpgrade(db: SQLiteDatabase?, oldVersion: Int, newVersion: Int) {
}
fun insertData(user:User){
val db=this.writableDatabase
var cv=ContentValues().apply {
put(COL_NAME,user.name)
put(COL_AGE,user.age) }
var result=db?.insert(TABLE_NAME,null,cv)
if (result==-1.toLong())
Toast.makeText(context,"Failed", Toast.LENGTH_SHORT).show()
else
Toast.makeText(context,"Success",Toast.LENGTH_SHORT).show()
}
fun readData():MutableList<User>
{
var list:MutableList<User> = ArrayList()
val query="SELECT * FROM " + TABLE_NAME
val db=this.readableDatabase
val result= db.rawQuery(query,null)
if(result.moveToNext()){
do{
var user=User()
user.id=result.getString(result.getColumnIndex(COL_ID)).toInt()
user.name=result.getString(result.getColumnIndex(COL_NAME))
user.age=result.getString(result.getColumnIndex(COL_AGE)).toInt()
list.add(user)
}
while (result.moveToNext())
}
result.close()
db.close()
return list
}
}

package com.example.myapplication
import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val context= this
var db=DataBaseHandler(context)
val etvName:TextView=findViewById(R.id.etvName)
val etvAge:TextView=findViewById(R.id.etvAge)
val btn_insert:Button = findViewById(R.id.btn_insert)
btn_insert.setOnClickListener {
if(etvName.text.toString().length>0 &&etvAge.text.toString().length>0){
var user=User(etvName.text.toString(),etvAge.text.toString().toInt())
db.insertData(user)
}
else(Toast.makeText(context,"Please fill all data",Toast.LENGTH_SHORT).show())
}
val btn_read:Button
btn_read=findViewById(R.id.btn_read)
btn_read.setOnClickListener {
var data=db.readData()
val tvResult:TextView
tvResult=findViewById(R.id.tvResult)
for (i in 0..data.size-1){
tvResult.append(data.get(i).id.toString() + "  " + data.get(i).name + "  " + data.get(i).age)
}
}
}
}

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<EditText
android:id="@+id/etvName"
android:layout_width="140dp"
android:layout_height="71dp"
android:text="Name"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.174"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.042" />
<EditText
android:id="@+id/etvAge"
android:layout_width="138dp"
android:layout_height="75dp"
android:text=""
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.857"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.035"
tools:text="Age" />
<Button
android:id="@+id/btn_insert"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="insert"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.495"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.169"
tools:ignore="MissingConstraints" />
<Button
android:id="@+id/btn_read"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Display"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.123"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.256"
tools:ignore="MissingConstraints" />
<Button
android:id="@+id/btn_update"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="update"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.256"
tools:ignore="MissingConstraints" />
<Button
android:id="@+id/btn_delete"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="delete"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.879"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.256"
tools:ignore="MissingConstraints" />
<TextView
android:id="@+id/tvResult"
android:layout_width="368dp"
android:layout_height="46dp"
android:gravity="center"
android:text="TextView"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.627"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.411" />
</androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

我建议您使用Room库，这是处理数据库的最简单方法。以下是您可以在上学习的链接：

https://developer.android.com/codelabs/android-room-with-a-view-kotlin#0

还有一件事，如果您使用kotlin，请不要在User类中创建构造函数(我猜这是一个模型(。只需使用数据类，它就可以在后台自动创建构造函数。

data class User(var id:Int=0,
var name:String="",
var age:Int=0)

kotlin使代码变得简单