我正在使用mac上的xamarin studio创建一个简单的由sqlite驱动的应用程序。数据库不会在使用xamarin构建之间持久保存ios
sqlite文件在“个人”文件夹中创建,并在构建之间保留,但是当我运行应用程序时,我在前一个调试会话中创建的表已不存在?
在我的代码中,在检查文件存在后,我使用sqliteconnection进行连接,并创建一个表并使用命令对象中的executenonquery方法插入一行。虽然在相同的上下文中,我可以使用第二个命令对象查询表,但是如果我停止调试器并重新启动表,我走了?
我应该在不同的文件夹中的文件,它是在Xamarin或ios保持表的设置?我无意中在sqlite中使用临时表或者可能是什么问题?
注意:到目前为止,我只使用starter版本的xamarin并在iphone模拟器上进行调试。
public class BaseHandler
{
private static bool DbIsUpToDate { get; set; }
const int DB_VERSION = 1; //Created DB
const string DB_NAME = "mydb.db3";
protected const string CNN_STRING = "Data Source=" + DB_NAME + ";Version=3";
public BaseHandler()
{
//No need to validate database more than once on each restart.
if (DbIsUpToDate)
return;
CheckAndCreateDatabase(DB_NAME);
int userVersion = GetUserVersion();
UpdateDBToVersion(userVersion);
DbIsUpToDate = true;
}
int GetUserVersion()
{
int version = 0;
using (var cnn = new SqliteConnection(CNN_STRING))
{
cnn.Open();
using (var cmd = cnn.CreateCommand())
{
cmd.CommandText = "CREATE TABLE UVERSION (VERSION INTEGER);" +
"INSERT INTO UVERSION (VERSION) VALUES(1);";
cmd.ExecuteNonQuery();
}
using (var cmd = cnn.CreateCommand())
{
cmd.CommandText = "SELECT VERSION FROM UVERSION;";
var pragma = cmd.ExecuteScalar();
version = Convert.ToInt32((long)pragma);
}
}
return version;
}
void UpdateDBToVersion(int userVersion)
{
//Prepare the sql statements depending on the users current verion
var sqls = new List<string>();
if (userVersion < 1)
{
sqls.Add("CREATE TABLE IF NOT EXISTS MYTABLE ("
+ " ID INTEGER PRIMARY KEY, "
+ " NAME TEXT, "
+ " DESC TEXT "
+ ");");
}
//Execute the update statements
using (var cnn = new SqliteConnection(CNN_STRING))
{
cnn.Open();
using (var trans = cnn.BeginTransaction(System.Data.IsolationLevel.ReadCommitted))
{
foreach(string sql in sqls)
{
using (var cmd = cnn.CreateCommand())
{
cmd.CommandText = sql;
cmd.ExecuteNonQuery();
}
}
trans.Commit();
//SetUserVersion(DB_VERSION);
}
}
}
protected string GetDBPath (string dbName)
{
// get a reference to the documents folder
var documents = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
// create the db path
string db = Path.Combine (documents, dbName);
return db;
}
protected void CheckAndCreateDatabase (string dbName)
{
var dbPath = GetDBPath(dbName);
// determine whether or not the database exists
bool dbExists = File.Exists(dbPath);
if (!dbExists)
SqliteConnection.CreateFile(dbPath);
}
}
同样,我的问题是,每次我运行调试器时它运行GetUserVersion但该表UVERSION不会话之间持续存在。 “File.Exists(dbPath)”返回true,所以CreateFile不运行。为什么数据库是空的?
听起来你的初始化代码每次都在运行。你可以发布代码示例吗? – Jason 2013-05-13 23:53:35