How to check if connection string is valid?

I'm writing an application where a user provides a connection string manually and I'm wondering if there is any way that I could validate the connection string - I mean check if it's correct and if the database exists.

You could try to connect? For quick (offline) validation, perhaps use DbConnectionStringBuilder to parse it...

    DbConnectionStringBuilder csb = new DbConnectionStringBuilder();
    csb.ConnectionString = "rubb ish"; // throws

But to check whether the db exists, you'll need to try to connect. Simplest if you know the provider, of course:

    using(SqlConnection conn = new SqlConnection(cs)) {
        conn.Open(); // throws if invalid
    }

If you only know the provider as a string (at runtime), then use DbProviderFactories:

    string provider = "System.Data.SqlClient"; // for example
    DbProviderFactory factory = DbProviderFactories.GetFactory(provider);
    using(DbConnection conn = factory.CreateConnection()) {
        conn.ConnectionString = cs;
        conn.Open();
    }

Try this.

    try 
    {
        using(var connection = new OleDbConnection(connectionString)) {
        connection.Open();
        return true;
        }
    } 
    catch {
    return false;
    }

If the goal is validity and not existence, the following will do the trick:

try
{
    var conn = new SqlConnection(TxtConnection.Text);
}
catch (Exception)
{
    return false;
}
return true;

For sqlite use this: Suppose you have connection string in textbox txtConnSqlite

     Using conn As New System.Data.SQLite.SQLiteConnection(txtConnSqlite.Text)
            Dim FirstIndex As Int32 = txtConnSqlite.Text.IndexOf("Data Source=")
            If FirstIndex = -1 Then MsgBox("ConnectionString is incorrect", MsgBoxStyle.Exclamation, "Sqlite") : Exit Sub
            Dim SecondIndex As Int32 = txtConnSqlite.Text.IndexOf("Version=")
            If SecondIndex = -1 Then MsgBox("ConnectionString is incorrect", MsgBoxStyle.Exclamation, "Sqlite") : Exit Sub
            Dim FilePath As String = txtConnSqlite.Text.Substring(FirstIndex + 12, SecondIndex - FirstIndex - 13)
            If Not IO.File.Exists(FilePath) Then MsgBox("Database file not found", MsgBoxStyle.Exclamation, "Sqlite") : Exit Sub
            Try
                conn.Open()
                Dim cmd As New System.Data.SQLite.SQLiteCommand("SELECT * FROM sqlite_master WHERE type='table';", conn)
                Dim reader As System.Data.SQLite.SQLiteDataReader
                cmd.ExecuteReader()
                MsgBox("Success", MsgBoxStyle.Information, "Sqlite")
            Catch ex As Exception
                MsgBox("Connection fail", MsgBoxStyle.Exclamation, "Sqlite")
            End Try
          End Using

I think you can easilly convert it to c# code