我遇到以下代码的更新部分问题。插入工作正常。当我添加用于存储在数据库中的整数的加/减的更新方法时，代码不再有效。它说应用程序已经关闭了。该应用程序甚至没有打开。请检查更新方法并进行充分更改。
首先我使用此代码接受姓名和电子邮件。然后将此代码更改为接受号码和电子邮件。变量名称和列名称尚未更改。请不要混淆这些。
谢谢。MainActivity.java
package com.sqltut;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends Activity {
Button save,load,updatebtn;
EditText name,email,update;
DataHandler handler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
save=(Button) findViewById(R.id.save);
load=(Button) findViewById(R.id.load);
name=(EditText) findViewById(R.id.name);
email=(EditText) findViewById(R.id.email);
save.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
String getName=name.getText().toString();
String getEmail=email.getText().toString();
int number = Integer.parseInt(getName);
handler=new DataHandler(getBaseContext());
handler.open();
long id=handler.insertData(number, getEmail);
Toast.makeText(getBaseContext(), "Data Inserted", Toast.LENGTH_LONG).show();
handler.close();
}
});
load.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
String getEmail;
Integer getName;
getName=0;
getEmail="";
handler=new DataHandler(getBaseContext());
handler.open();
Cursor C=handler.returnData();
if(C.moveToFirst())
{
do
{
getName=C.getInt(0);
getEmail=C.getString(1);
}while(C.moveToNext());
}
handler.close();
Toast.makeText(getBaseContext(), "Name:"+getName+" And Email:"+getEmail,Toast.LENGTH_LONG).show();
}
});
updatebtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
int number,flag=0; //flag to check for addition or subtraction
String getupdate=update.getText().toString();
number=Integer.parseInt(getupdate);
handler=new DataHandler(getBaseContext());
handler.open();
handler.updateData(number,flag);
//subtraction: flag=0, addition: flag=1
handler.close();
}
});
//to call next activity
/* Button createAppointment = (Button)findViewById(R.id.Next);
createAppointment.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent myIntent = new Intent(MainActivity.this, Page2.class);
MainActivity.this.startActivity(myIntent);
}
});
*/ }
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
DataHandler.java
package com.sqltut;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DataHandler {
public static final String NAME="name";
public static final String EMAIL="email";
public static final String TABLE_NAME="mytable";
public static final String DATA_BASE_NAME="mydatabase";
public static final int DATABASE_VERSION=1;
public static final String TABLE_CREATE="create table mytable(name text not null, email text not null);";
DataBaseHelper dbhelper;
Context ctx;
SQLiteDatabase db;
public DataHandler(Context ctx)
{
this.ctx = ctx;
dbhelper=new DataBaseHelper(ctx);
}
private static class DataBaseHelper extends SQLiteOpenHelper
{
public DataBaseHelper(Context ctx)
{
super(ctx,DATA_BASE_NAME,null,DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
try{
db.execSQL(TABLE_CREATE);
}
catch(SQLException e)
{
e.printStackTrace();
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS mytable ");
onCreate(db);
}
}
public DataHandler open()
{
db=dbhelper.getWritableDatabase();
return this;
}
public void close()
{
dbhelper.close();
}
public long insertData(Integer name, String email)
{
ContentValues content=new ContentValues();
content.put(NAME, name);
content.put(EMAIL,email);
return db.insert(TABLE_NAME, null, content);
}
public void updateData(Integer number,Integer flag)
{
db = dbhelper.getReadableDatabase();
String select = "select name from " + TABLE_NAME ;
Cursor c = db.rawQuery(select, null);
int current=0;
if (c.moveToFirst()) {
current= Integer.parseInt(c.getString(0));
}
if(flag==0)//subtraction
{
current=current-number;
}
else//addition
{
current=current+number;
}
c.close();
db.close();
db = dbhelper.getReadableDatabase();
ContentValues content=new ContentValues();
content.put(NAME, current);
db.update(TABLE_NAME, content,null,null);
}
public Cursor returnData()
{
return db.query(TABLE_NAME, new String[] {NAME,EMAIL}, null, null, null, null, null);
}
}
已编辑的updateData（）
public void updateData(Integer value,Integer flag)
{
db = dbhelper.getReadableDatabase();
String selectQuery = "select balance from " + TABLE_NAME ;
Cursor cursor = db.rawQuery(selectQuery, null);
int current = 0;
if (cursor.moveToFirst()) {
current= Integer.parseInt(cursor.getString(0));
}
if(flag==0){
current = current-value;
}else {
current = current+value ;
}
cursor.close();
db.close();
try{
db = dbhelper.getWritableDatabase();
String rawQuery = "update mytable set balance="+current;
db.rawQuery(rawQuery, null);
}
catch(Exception ex)
{
ex.printStackTrace();
}
}
代码有效。 db.rawQuery(rawQuery, null);已更改为db.execSQL(rawQuery);
答案 0 :(得分：2)
您可以通过以下方法更新表格中的任何值：
public void updateInteger(Integer newID)
{
try{
sqliteDb = appDb.getWritableDatabase();
String rawQuery = "update <table_name> set id="+newID;
sqliteDb.rawQuery(rawQuery, null);
Log.v(TAG, "ID updated");
}
catch(Exception ex)
{
ex.printStackTrace();
}
}