【发布时间】：2022-06-22 06:41:11
【问题描述】：
所以我在网上找到了一个视频https://www.youtube.com/watch?v=sq45s9gggsw，它会引导您完成简单显示 SQLite 数据库的整个过程，一旦我把它弄下来，我就可以继续前进，但我似乎无法让它工作。每次说找不到我正在查询的表时，程序都会崩溃，但似乎所有的 try catch 语句都被忽略了，因为我从资产文件夹中删除了数据库，但它仍然给我相同的响应.我已经研究了好几个小时了，看不出她发生了什么是我的代码
主要活动
package com.example.testdatabase;
import androidx.appcompat.app.AppCompatActivity;
import android.widget.TextView;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity {
TextView lst;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
lst = (TextView) findViewById(R.id.list);
MyDBHandler dbHandler = new MyDBHandler(this,null,null,2);
lst.setText(dbHandler.loadHandler());
}
}
数据库处理程序
package com.example.testdatabase;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.IOException;
public class MyDBHandler extends SQLiteOpenHelper{
public static final int DB_VERSION = 2;
private static final String DB_NAME = "student.db";
private static String DB_PATH = "/data/user/0/com.example.testdatabase/databases/";
SQLiteDatabase myDataBase;
private final Context mContext;
public MyDBHandler(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, DB_NAME, factory, DB_VERSION);
this.mContext = context;
}
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int i, int i1) {
}
private boolean checkDatabase(){
try {
final String mPath = DB_PATH + DB_NAME;
final File file = new File(mPath);
if (file.exists())
return true;
else
return false;
} catch (SQLiteException e){
e.printStackTrace();
return false;
}
}
private void copyDatabase() throws IOException{
try{
InputStream mInputStream = mContext.getAssets().open(DB_NAME);
String outFileName = DB_NAME;
OutputStream mOutputStream = new FileOutputStream(outFileName);
byte[] buffer = new byte[1024];
int length;
while((length = mInputStream.read(buffer)) > 0){
mOutputStream.write(buffer,0,length);
}
mOutputStream.flush();
mOutputStream.close();
}
catch (Exception e){
e.printStackTrace();
}
}
public void createDatabase() throws IOException{
boolean mDatabaseExist = checkDatabase();
if (!mDatabaseExist){
this.getReadableDatabase();
this.close();
try{
copyDatabase();
}
catch(IOException mIOException){
mIOException.printStackTrace();
throw new Error("Error copying Database");
} finally {
this.close();
}
}
}
@Override
public synchronized void close(){
if (myDataBase != null)
myDataBase.close();
SQLiteDatabase.releaseMemory();
super.close();
}
public String loadHandler(){
try{
createDatabase();
}
catch (IOException e){
e.printStackTrace();
}
String result = "";
SQLiteDatabase db = this.getReadableDatabase();
Cursor c = db.rawQuery("select * from Student", null);
while(c.moveToNext()){
int result_id = c.getInt(0);
String result_name = c.getString(1);
result += String.valueOf(result_id) + " " + result_name + System.getProperty("line.separator");
}
c.close();
db.close();
return result;
}
}
视频还让你创建了一个我看不到的学生班级
package com.example.testdatabase;
public class Student {
private int _id;
private String _studentName;
public Student(int id, String studentName){
this._id = id;
this._studentName = studentName;
}
public void setID(int id){
this._id = id;
}
public int getID(){
return this._id;
}
public void setStudentName(String studentName){
this._studentName = studentName;
}
public String getStudentName(){
return this._studentName;
}
}
我在调试中不断得到 E/SQLiteLog 的结果：(1) 没有这样的表：学生 在调用 SQL 查询的 loadHandler 方法中出现错误。似乎它正在跳过所有的 try/catch 语句来检查数据库是否存在。
任何帮助将不胜感激
【问题讨论】：
标签： android sqlite android-studio android-sqlite