I would appreciate some help with async/Task implementation in my Windows Form application.
In this app, I retrieve data from the datacenter SQl server database using WCF services, so part of this code runs on the client and some on the datacenter server where it retrieves the data and returns it. I’d like to optimize the code using async/Task on the clien or server or preferably both. The example code starts with a Windows Form with a button, when the button is clicked it gets a value from the database, displays it and updates a local variable.
I’m not clear if I can simply implement async/Task and Task.Run in the first button click event or whether the code should be cascaded through all methods, or something in between. I'm also not clear on how to handle the wcf service.
I’ve created a simplified example of the code, pretty close to sequentially.
In this code, the return value updates the windows form. I’d like to see how this code is optimized using async/Task await for this purpose and what would be different if the code did not return a value.
public partial class Form1 : Form
{
int returnvalue = 0;
public Form1()
{
InitializeComponent();
}
private void btnGetResult_Click(object sender, EventArgs e)
{
int rowcount = ChangeProductPrice(.05m);
txtResult.Text = rowcount.ToString();
}
private int ChangeProductPrice(decimal priceincrease)
{
int rv = MyData.WebServiceObject.ChangePrice(priceincrease);
UpdateLocalVariables(rv);
return rv;
}
private void UpdateLocalVariables(int rv)
{
returnvalue = rv;
}
}
public static class MyData
{
private static IMyDataWCFService _webserviceobject = null;
public static IMyDataWCFService WebServiceObject
{
get
{
if (_webserviceobject is null)
{
//...code to initialize it
}
return _webserviceobject;
}
}
}
[ServiceContract(SessionMode = SessionMode.Required)]
public interface IMyDataWCFService
{
[OperationContract]
int ChangePrice(decimal priceincrease);
}
[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession, ConcurrencyMode = ConcurrencyMode.Multiple)]
public class MyDataWCFService : IMyDataWCFService
{
private MyDataService _serviceObject = null;
private MyDataService ServiceObject
{
get
{
if (_serviceObject == null)
{
_serviceObject = new MyDataService();
}
return _serviceObject;
}
}
public int ChangePrice(decimal priceincrease)
{
return ServiceObject.ChangePrice(priceincrease);
}
}
public class MyDataService //running on server
{
public int ChangePrice(decimal priceincrease)
{
int rows = 0;
SqlConnection conn = null;
try
{
conn = this.GetSqlConnection();
using (SqlCommand cmd = new SqlCommand())
{
cmd.CommandType = CommandType.StoredProcedure;
cmd.Connection = conn;
cmd.CommandText = "mysp_UpdatePrice";
cmd.Parameters.Add(new SqlParameter("#Rate", priceincrease));
conn.Open();
rows = cmd.ExecuteNonQuery();
}
}
catch (Exception ex)
{
ProcessError(ex);
}
finally
{
if (conn != null)
ReturnSqlConnection(conn);
}
return rows;
}
private SqlConnection GetSqlConnection()
{
//dostuff;
return new SqlConnection();
}
private void ProcessError(Exception ex)
{
//dostuff;
}
private void ReturnSqlConnection(SqlConnection conn)
{
//dostuff;
}
}
Related
I've got four main files in play here: Form 1, which is called frmLogin, Form2, which is called frmUserHome, a class called DbConnector.cs and a class called BankAccount.cs
The program works as follows: Form1 calls method from DBConnector -> DB Connector method fills an object and it's variables which is instantiated in DBConnector. This object is of class BankAccount.cs
Then, after the method finishes and if successful, Form1 instantiates Form2 and it opens. In form2 is where I want to access the object that was created in the DBconnector class. How do I do this? I've tried instantiating new objects of BankAccount.cs in there, I've tried all these different constructor stuff I've seen on here. Nothing seems to be working.
For reference: the object is populated when it runs in Dbconnector. However, when I try to receive data when I use it in Form2, all of the fields are NULL.
I've made countless adjustments from reading different posts on here so the code is rightfully a mess now and probably extremely unorganised.
Here's the main portions of my code below:
Form1
namespace BankingSystem
{
public partial class frmLogIn : Form
{
public BankAccount myBankAccount = new BankAccount();
dbConnector newConnector;
public frmLogIn()
{
InitializeComponent();
timerMain.Enabled = true;
timerMain.Start();
}
private void btnLogIn_Click(object sender, EventArgs e)
{
try
{
newConnector.CheckDetailsLogin(accountNumTextBox.Text, pinNumTextBox.Text);
frmUserHome UserHome = new frmUserHome();
MessageBox.Show("Success! Happy Banking!");
UserHome.ShowDialog();
}
catch
{
MessageBox.Show("Failed - incorrect login details.");
}
}
}
}
DBConnector Class:
namespace BankingSystem
{
public class dbConnector
{
Boolean isCorrect = false;
private static SQLiteConnection sqlconnConnection;
public BankAccount myBankAccount = new BankAccount();
public DataSet myAppDataSet = new DataSet(); // created for you to use and push data into
public dbConnector(string strFilePath)
{
try
{
sqlconnConnection = new SQLiteConnection("Data Source=" + strFilePath);
}
catch (Exception ex)
{
throw new Exception("DbConnector initialisation unsuccessful:\n" + ex.Message);
}
}
public void CheckDetailsLogin(string strAccno, string strPin)
{
// this is where check ou the boiler plate code and adjst to my APP.
try
{
DataTable dtUser = new DataTable();
sqlconnConnection.Open();
string strQuery2 = #"SELECT * FROM Accounts WHERE Account_Number='"+ strAccno +"' AND PIN='"+ strPin +"';"; // example of a parametrised SQL statement.
SQLiteCommand sqlcomCommand2 = new SQLiteCommand(strQuery2, sqlconnConnection);
SQLiteDataAdapter sqldatadptAdapter = new SQLiteDataAdapter(sqlcomCommand2); // local SQL data Adaptor
try
{
sqldatadptAdapter.Fill(dtUser);
}
catch (Exception ex)
{
// Exception will the "thrown"/Raised when there was a problem
throw new Exception($"SELECT unsuccessful:\n{ex.Message}");
}
finally
{
sqlconnConnection.Close();
}
if (dtUser.Rows.Count == 0)
{
// the record set comes back with no records found, an empty Datatable with no rows
// means there was no data matching your query
throw new Exception("No Such Bank user found");
}
else
{
// change to your applications needs
// Rows[0] - we are expecting at least 1 row, and its basically an array so we address
// the first element with 0
// Rows[0]["fieldnamefromDB"] <- referencing the column in the DB
//this.strID = strUserID;
myBankAccount.AccountNumber = dtUser.Rows[0]["Account_Number"].ToString();
myBankAccount.AccountPin = dtUser.Rows[0]["PIN"].ToString();
myBankAccount.AccountBalance = Convert.ToDecimal(dtUser.Rows[0]["Balance"]);
myBankAccount.AccountHolder = dtUser.Rows[0]["First_Name"].ToString();
myBankAccount.AccountAddress = dtUser.Rows[0]["Home_Address"].ToString();
myBankAccount.MyAccountGUID = dtUser.Rows[0]["GUID"].ToString();
if (myBankAccount.AccountNumber == strAccno && myBankAccount.AccountPin == strPin)
{
isCorrect = true;
}
else
{
isCorrect = false;
}
//myLocalBankAccUsr
}
}
catch (Exception ex)
{
// exception thrown for the whole method or function
throw new Exception($"User(string):\n{ex.Message}");
}
}
BankAccount.cs class
namespace BankingSystem
{
public class BankAccount
{
private string accountNumber;
private decimal accountBalance;
private string accountHolder;
private string accountPhoneNumber;
private string accountAddress;
private string accountPin;
private string myAccountGUID;
// private string AccountHolderGUID;
// private string AccountTypeGUID;
public string AccountNumber
{
get { return accountNumber; }
set { accountNumber = value; }
}
public decimal AccountBalance
{
get { return accountBalance; }
set { accountBalance = value; }
}
public string AccountHolder
{
get { return accountHolder; }
set { accountHolder = value; }
}
public string AccountPhoneNumber
{
get { return accountPhoneNumber; }
set { accountPhoneNumber = value; }
}
public string AccountAddress
{
get { return accountAddress; }
set { accountAddress = value; }
}
public string AccountPin
{
get { return accountPin; }
set { accountPin = value; }
}
public string MyAccountGUID
{
get { return myAccountGUID; }
set { myAccountGUID = value; }
}
public Boolean CanWithDrawAmount(decimal AmountToTransfer)
{
if (AmountToTransfer > this.AccountBalance){
return false;
}else
{
return true;
}
}
public void UpdatePIN()
{
// connect to bank DB connector
// send it the new pin
// SQL update command
}
}
}
Here is Form2:
namespace BankingSystem
{
public partial class frmUserHome : Form
{
public frmUserHome()
{
InitializeComponent();
tabMainForm.Appearance = TabAppearance.FlatButtons;
tabMainForm.ItemSize = new Size(0, 1);
tabMainForm.SizeMode = TabSizeMode.Fixed;
timerMain.Enabled = true;
timerMain.Start();
}
private void frmUserHome_Load(object sender, EventArgs e)
{
labelWelcome.Text = "Welcome "; //newMainBank.AccountHolder;
}
The 'labelWelcome.Text = "Welcome" is where I want the name stored inside the object to be used. So it should ideally access the BankAccount class, access the AccountHolder field and use that field to concat onto the end of the 'Welcome' text. However, it just shows 'Welcome' and no name on the end, when I run the program (because all values get reset to null in form2.. for some reason)
Below I have updated the code for Form1 and Form2.
Form 1
namespace BankingSystem
{
public partial class frmLogIn : Form
{
dbConnector newConnector;
public frmLogIn()
{
InitializeComponent();
newConnector = new dbConnector(**pass str file path**);
timerMain.Enabled = true;
timerMain.Start();
}
private void btnLogIn_Click(object sender, EventArgs e)
{
try
{
newConnector.CheckDetailsLogin(accountNumTextBox.Text, pinNumTextBox.Text);
frmUserHome UserHome = new frmUserHome(newConnector.myBankAccount);
MessageBox.Show("Success! Happy Banking!");
UserHome.ShowDialog();
}
catch
{
MessageBox.Show("Failed - incorrect login details.");
}
}
}
}
Form 2
namespace BankingSystem
{
public partial class frmUserHome : Form
{ public BankAccount _bankAccount;
public frmUserHome(BankAccount bankAccount)
{
InitializeComponent(); _bankAccount = bankAccount;
tabMainForm.Appearance = TabAppearance.FlatButtons;
tabMainForm.ItemSize = new Size(0, 1);
tabMainForm.SizeMode = TabSizeMode.Fixed;
timerMain.Enabled = true;
timerMain.Start();
}
private void frmUserHome_Load(object sender, EventArgs e)
{
labelWelcome.Text = "Welcome "+ bankAccount.AccountHolder;
}
I want to access the openConnection from my dbconnect class from by other form but it does not work properly. I have to copy-paste the entire Oopenconnection to the other page for them to access it.
class dbconnect
class DB_Connect
{
private MySqlConnection connection;
private string server;
private string database;
private string uid;
private string password;
//Constructor
public DB_Connect()
{
Initialize();
}
//Initialize values
private void Initialize()
{
server = "localhost";
database = "xyz";
uid = "root";
password = "";
string connectionString = $"datasource=127.0.0.1;port = 3306; SERVER={server}; DATABASE={database}; USERNAME={uid}; PASSWORD={password};sslmode=none";
connection = new MySqlConnection(connectionString);
}
//open connection to database
public bool OpenConnection()
{
try
{
connection.Open();
return true;
}
catch (MySqlException ex)
{
switch (ex.Number)
{
case 0:
MessageBox.Show("Cannot connect to server. Contact administrator");
break;
case 1045:
MessageBox.Show("Invalid username/password, please try again");
break;
}
return false;
}
}
//Close connection
public bool CloseConnection()
{
try
{
connection.Close();
return true;
}
catch (MySqlException ex)
{
MessageBox.Show(ex.Message);
return false;
}
}
}
MyForm 2
On click data is being displayed on dataGridView
private void display_record_Click(object sender, EventArgs e)
{
DB_Connect connect = new DB_Connect(); // I believe this part does not work
string show_query = "SELECT * FROM testing_tb";
if (connect.OpenConnection() == true)
{
using (MySqlCommand cmd_DB = new MySqlCommand(show_query, connection))
{
try
{
using (MySqlDataReader reader = cmd_DB.ExecuteReader())
if (reader.HasRows)
{
dt = new DataTable();
dt.Load(reader);
dataGridView1.DataSource = dt;
}
else
{
MessageBox.Show("No data record detected");
}
connect.CloseConnection();
}
catch (Exception ex)
{
MessageBox.Show("Could not connect to database!\n" + ex, "Database Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
}// end of catch
} // end of MySQLCommand
} // end of connection check
}
I want to access data from my dtconnect class so that I do not have to paste public bool OpenConnection(){} in every new form that I want to open connection.
Error: could not connect to database, connection must be valid and open, etc..
If you really want the connection available everywhere you can use this:
public static class Connection
{
private const string ConnectionString = "YOUR CONNECTION";
public static System.Data.SqlClient.SqlConnection Conn { get; private set; } = null;
public static void Open()
{
try
{
Conn = new System.Data.SqlClient.SqlConnection(ConnectionString);
Conn.Open();
}
catch { System.Windows.MessageBox.Show("Can't connect to the server, please check if you have an internet connection."); }
}
public static void Close() { Conn.Close(); }
}
It is not recommended because your connection will be open at all time so you should do this instead:
public static class Connection
{
private const string ConnectionString = "YOUR CONNECTION";
public static System.Data.SqlClient.SqlConnection Conn { get; private set; } = null;
public static void Create() { Conn = new System.Data.SqlClient.SqlConnection(ConnectionString); }
public static void Open()
{
try { Conn.Open(); }
catch { System.Windows.MessageBox.Show("Can't connect to the server, please check if you have an internet connection."); }
}
public static void Close() { Conn.Close(); }
}
And you open and close your connection when needed.
So basically, when you open your connection when using a query you use Connection.Open() and Connection.Close(). It is now accessible from everywhere if the class is in the using of your forms.
Here's a link about the connection state: https://softwareengineering.stackexchange.com/questions/142065/creating-database-connections-do-it-once-or-for-each-query
I'm trying to notify multiple application users connected to the same SQLServer that change happened on certain data base table. I decided to use SQLDependency class because it seemed like the best way to do so, but I can't get it to work. Your help is very much appreciated.
First of all I created SqlWatcher class to simplify the usage (credits go to this blog):
public class SqlWatcher : IDisposable
{
public delegate void SqlWatcherEventHandler(DataSet Result);
public event SqlWatcherEventHandler OnChange;
private string ConnectionString;
private SqlConnection Connection;
private SqlCommand Command;
private SqlDataAdapter Adapter;
private DataSet Result;
public SqlWatcher(string ConnectionString, SqlCommand Command)
{
this.ConnectionString = ConnectionString;
SqlDependency.Start(this.ConnectionString);
this.Connection = new SqlConnection(this.ConnectionString);
this.Connection.Open();
this.Command = Command;
this.Command.Connection = this.Connection;
Adapter = new SqlDataAdapter(this.Command);
}
public void ChangeEventWrapper(object state)
{
DataSet Result = (DataSet)state;
OnChange(Result);
}
public void Dispose()
{
Stop();
}
private void RegisterForChanges()
{
//Remove old dependency object
this.Command.Notification = null;
//Create new dependency object
SqlDependency dep = new SqlDependency(this.Command);
dep.OnChange += new OnChangeEventHandler(Handle_OnChange);
//Save data
Result = new DataSet();
Adapter.Fill(Result);
OnChange(Result);
}
public void Start()
{
RegisterForChanges();
}
public void Stop()
{
SqlDependency.Stop(this.ConnectionString);
}
private void Handle_OnChange(object sender, SqlNotificationEventArgs e)
{
SqlDependency dep = (SqlDependency)sender;
dep.OnChange -= Handle_OnChange;
RegisterForChanges();
}
public DataSet DataSet
{
get { return Result; }
}
}
From the main form user can add an item to the targeted SqlDependency command table and when that happens I want new form to pop-up with news. This is what my main form looks like:
public partial class MainForm: Form
{
private string connectionString = #"data source = .\sqlexpress; initial catalog = Sample1; integrated security = true";
private static SqlWatcher SqlQueueWatcher;
public MainForm()
{
InitializeComponent();
InitializeSqlDependency();
}
private void InitializeSqlDependency()
{
SqlCommand cmd = new SqlCommand();
cmd = new SqlCommand("SELECT ID, Text FROM dbo.Notifications");
cmd.CommandType = CommandType.Text;
//Setup the SQLWatcher
SqlQueueWatcher = new SqlWatcher(connectionString, cmd);
SqlQueueWatcher.OnChange += new SqlWatcher.SqlWatcherEventHandler(QueueSQLWatcher_OnChange);
SqlQueueWatcher.Start();
}
private static void QueueSQLWatcher_OnChange(DataSet Result)
{
NotificationForm notificationForm = new NotificationForm(Result);
notificationForm.Show();
}
private void MainForm_FormClosing(object sender, FormClosingEventArgs e)
{
SqlQueueWatcher.Dispose();
}
I expected this to work the way that when any user adds data to the Notifications data base other users get notified via NotificationForm. Could anyone tell me what am I doing wrong? I've been trying to figure it out myself for 2 days now.
Thanks in advance!
P.S. If you have better idea on doing the same notification concept, feel free to express yourself.
I trying to develop a windows form application. In here I want to call a variable both form 1 and form 2. I got the vale to ComputerId variable.
namespace ComData
{
public partial class addnew : Form
{
string ConnString = "Server=localhost;Database=machinedetails;UID=root;Encrypt=true;";
public int ComputerId { get; set; }
public addnew()
{
InitializeComponent();
}
private void btnnext_Click(object sender, EventArgs e)
{
using (MySqlConnection conn = new MySqlConnection(ConnString))
{
using (MySqlCommand comm = new MySqlCommand())
{
if (this.txtbranch.Text != "" && this.txtcostcenter.Text != "")
{
try
{
MySqlParameter branchparam = new MySqlParameter("#branch", MySqlDbType.VarChar, 16);
MySqlParameter costcenterparam = new MySqlParameter("#costcenter", MySqlDbType.VarChar, 16);
comm.Connection = conn;
conn.Open();
comm.CommandText = "INSERT INTO computerdetails(branch,costcenter) VALUES (#branch, #costcenter);Select last_insert_id();";
comm.Parameters.Add(branchparam);
comm.Parameters.Add(costcenterparam);
comm.Prepare();
String branch = txtbranch.Text;
String costcenter = txtcostcenter.Text;
comm.Parameters[0].Value = branch;
comm.Parameters[1].Value = costcenter;
MySqlDataReader reader = comm.ExecuteReader();
if (reader.HasRows)
{
reader.Read();
ComputerId = Convert.ToInt32(reader[0]);
MessageBox.Show("value is" + ComputerId);
}
this.Hide();
newdetails nd = new newdetails();
nd.ShowDialog();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
else
{
MessageBox.Show("Please fill the values");
}
}
}
}
}
}
I want to know how to call this ComputerId variable in form 2. Please help me.. Thanks..
This code-block belongs to the form2 where you open your addnew-form
addnew testObj = new addnew(); //init
testObj.show() //or testObj.showDialog();
int id = testObj.ComputerId; //getting the id
You can add a parameterized constructor to newdetails form. And then pass the integer value there. Something like this:
// In newdetails form
private int computerId;
public newdetails(int compId){
computerId = compId;
}
// in addnew form
newdetails nd = new newdetails(ComputerId);
In newdetails form:
private addNew _addNew { get; set; }
public newdetails(addNEw parent)
{
InitializeComponent();
_addNew = parent;
}
//you can access any public variable at addNew form with:
int test = _addNew.PublicVariableName
in your addnew form:
newetails x = new newdetails(this);
x.Show();
I will recommend you to move the ComputerId variable to "Program Class" inside Program.cs file, like this:
public class Program
{
public static int ComputerId;
//Main and other methods......
}
Now you can access this variable from all of your forms simply like this:
int cid=Program.ComputerId;
As Simple As That.
I have 2 classes: MyForm and Database
In MyForm I have a method to change a label text to show error:
public void printError(string text){
label1.Text = text;
}
My Database class needs to access that method too, so I make it static:
public static void printError(MyForm form, string text){
form.label1.Text = text;
}
Now the problem is, how do I call that method from Database class?
This question I found said that I need to pass MyForm into Database's contructor like this:
class MyForm : Form{
Database db;
public Form(){
db = new Database(this);
}
}
class Database{
MyForm form;
public Database(MyForm f){
form = f;
}
...
//then I can access the printError like this
MyForm.printError(form, "You got error");
}
I tried that and it freezes the form. Any other solution?
Thanks
Here is a very simple example of how you can achieve this without your data layer knowing about your UI:
class MyForm : Form
{
Database db;
public Form()
{
db = new Database(this);
}
public void DoSomething()
{
var errors = db.Login("", "");
if (errors.Any())
label1.Text = errors.First(); // Or you can display all all of them
}
}
class Database
{
public List<string> Login(string username, string password)
{
var errors = new List<string>();
if (string.IsNullOrEmpty(username))
errors.Add("Username is required");
if (string.IsNullOrEmpty(password))
errors.Add("Password is required");
[...]
return errors;
}
}
Like #Matthew Ferreira and others have stated the design is not idea, but here's something to get you started.
class MyForm : Form
{
public void SomeMethod()
{
var dataAccess = new Repository();
dataAccess.ExecuteQuery();
if (dataAccess.Exceptions.Any())
{
// display your error messages
form.label1.Text = dataAccess.Exceptions.Select(x => x.ToString());
}
}
}
class Repository
{
private readonly HashSet<Exception> _exceptions = new HashSet<Exception>();
public IEnumerable<Exception> Exceptions
{
get { return _exceptions; }
}
public int ExecuteQuery()
{
var numberOfRecordsAffected = 0;
try
{
// do something
}
catch (Exception ex)
{
// normall catching exceptions is a bad idea
// and you should really catch the exception at the
// layer best equiped to deal with it
_exceptions.Add(ex);
}
// but, for the purpose of this example we might want to add some logic to try the query on another database ????
try
{
// do something
}
catch (Exception ex)
{
_exceptions.Add(ex);
}
return numberOfRecordsAffected;
}
}
You need to look up "seperation of concerns". Its really bad to mix your UI code with you Database Access Layer (DAL). Better to bind the UI to business objects that are populated via a DAL.
To let the UI know about an error you could simply use a delegate.
namespace OperationErrorDelegate
{
public delegate void OperationErrorHandler(Exception ex);
public class DAL
{
public event OperationErrorHandler ReportError;
public void DoDALOperationThatCausesError()
{
try
{
int i = 1;
int j = 0;
int k = i/j;
}
catch (Exception ex)
{
ReportError(ex);
}
}
}
}
Add this code to the form:
using System ;
using System.Windows.Forms;
namespace OperationErrorDelegate
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
DAL DAL = new DAL();
DAL.ReportError += new OperationErrorHandler(DAL_OperationErrorProgress);
DAL.DoDALOperationThatCausesError();
}
private void DAL_OperationErrorProgress(Exception ex)
{
label1.Text = ex.Message;
}
}
}
Assuming the OP's requirement is to display an error message in a label, when the credentials are wrong:
private void btn_login_Click(object sender, EventArgs e)
{
MySqlConnection con = new MySqlConnection("server=localhost;uid=root;password=abc;database=mydb");
MySqlCommand cmd = new MySqlCommand("select * from emp where name='" + textBox1.Text + "'and pwd='" + textBox2.Text + "'",con);
con.Open();
MySqlDataReader dr = cmd.ExecuteReader();
if (dr.Read())
{ //successful
//navigate to next page or whatever you want
}
else
Label1.Text("Invalid userid or password");
con.Close();
}
And if you need error message for wrong data type (the user input string but the database column is Integer), then use validations at client side. You dont need to do it at backend, since that will be a burden.
You can use regular expressions for that in the button_click itself.