提问人：Felice Lombardi 提问时间：8/27/2016 更新时间：8/27/2016 访问量：913
如何知道可移植库 Xamarin Forms 项目中资源的相对路径？
how can I know relative path of a resource inside of a portable library Xamarin Forms project?
问：
我有一个关于 Xamarin Forms 的问题。
我正在开发我的第一个跨平台应用程序（iOS 和 Android），我选择创建一个 Form App 解决方案。
我的应用程序需要使用SQLite数据库，该数据库是在应用程序从FTP服务器启动时下载的。 如果无法访问服务器，则应用程序应使用我放在可移植库中的本地 SQLite 数据库。
为此，我在可移植库中创建了一个文件夹，并将SQLite文件放入其中。（这是正确的吗？或者我需要放入iOS / Android项目？
若要获得此本地数据库的连接字符串，我需要知道其路径。我怎么知道？
谢谢！
答：
0赞
MohamedHamza
8/27/2016
#1
为此，您应该在共享项目上实现接口，该接口将只有一个方法来检索连接，具体取决于每个设备上的路径，如下所示：
public interface ISQLite
{
SQLiteConnection GetConnection();
}
并在每个项目上实现此接口 - for Android：
[assembly: Dependency (typeof (SQLite_Android))]
namespace GenYouth.Droid
{
public class SQLite_Android : ISQLite
{
public SQLite_Android ()
{
}
#region ISQLite implementation
public SQLite.SQLiteConnection GetConnection ()
{
var sqliteFilename = "db_Name.db3";
string documentsPath = System.Environment.GetFolderPath (System.Environment.SpecialFolder.Personal); // Documents folder
var path = Path.Combine(documentsPath, sqliteFilename);
// This is where we copy in the prepopulated database
Console.WriteLine (path);
if (!File.Exists(path))
{
/*
var s = Forms.Context.Resources.OpenRawResource(Resource.Raw.GenYouth_db); // RESOURCE NAME ###
// create a write stream
FileStream writeStream = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Write);
// write to the stream
ReadWriteStream(s, writeStream);
* */
}
var conn = new SQLite.SQLiteConnection(path);
// Return the database connection
return conn;
}
#endregion
/// <summary>
/// helper method to get the database out of /raw/ and into the user filesystem
/// </summary>
void ReadWriteStream(Stream readStream, Stream writeStream)
{
int Length = 256;
Byte[] buffer = new Byte[Length];
int bytesRead = readStream.Read(buffer, 0, Length);
// write the required bytes
while (bytesRead > 0)
{
writeStream.Write(buffer, 0, bytesRead);
bytesRead = readStream.Read(buffer, 0, Length);
}
readStream.Close();
writeStream.Close();
}
}
}
对于IOS：
[assembly: Dependency (typeof (SQLite_iOS))]
namespace GenYouth.iOS
{
public class SQLite_iOS : ISQLite
{
public SQLite_iOS ()
{
}
#region ISQLite implementation
public SQLite.SQLiteConnection GetConnection ()
{
var sqliteFilename = "db_Name.db3";
string documentsPath = Environment.GetFolderPath (Environment.SpecialFolder.Personal); // Documents folder
string libraryPath = Path.Combine (documentsPath, "..", "Library"); // Library folder
var path = Path.Combine(libraryPath, sqliteFilename);
// This is where we copy in the prepopulated database
Console.WriteLine (path);
if (!File.Exists (path)) {
File.Copy (sqliteFilename, path);
}
var conn = new SQLite.SQLiteConnection(path);
// Return the database connection
return conn;
}
#endregion
}
}
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