I have two dropdownlists, ddlstates and ddlcitys.
The ddlstates has a list of Brazilian states that when clicked, loads the ddlcitys with the cities of that state. Until then, everything works correctly, but when clicking the save button which makes verification of completed fields or not, the ddlcitys back to the first option. How to store the information ddlcitys before the postback?
In code behind, have code that loads the ddlcitys:
protected void ddlstates_TextChanged(object sender, EventArgs e)
{
if (ddlstates.Text != "")
{
List<ListItem> cidades = new List<ListItem>();
SqlConnection conn = new SqlConnection(mytools.stringconection);
SqlDataReader dr = null;
conn.Open();
SqlCommand cmd = new SqlCommand("select ciddesc from cidades where cidestsigla = '" + ddlstates.SelectedValue.ToString() + "' order by 1 asc");
cmd.Connection = conn;
dr = cmd.ExecuteReader();
ddlcitys.Items.Clear();
while (dr.Read())
{
cidades.Add(new ListItem(dr[0].ToString()));
}
dr.Close();
conn.Close();
ddlcitys.DataTextField = "Text";
ddlcitys.DataValueField = "Value";
ddlcitys.DataSource = cidades;
ddlcitys.DataBind();
}
}
Asked long time ago, anyway may the answer help anyone.
On your page load event before bind any of your dropdownlists, make sure that not post back, then on your dropdown select change events , your dropdown values will not re bind so values will not changed.
hint : make sure that your aspx page enable view state (by default enabled) read more.
protected void Page_Load(object sender, EventArgs e) {
if (!IsPostBack) {
//this will called when your page loaded at first time, so bind your drop down values here.
} else {
//this will called on select change, don't bind your dropdown again, then values will be same (asp.net web forms viewstates will handle read more about viewstate).
}
}
Related
When I choose any option from the dropdown list and then insert it into the database, the first option is chosen automatically, even if I choose the second or third option; only the first option is inserted each time.
Order.aspx.cs
protected void selectList()
{
conn = new SqlConnection(connstr);
conn.Open();
sql = "SELECT * FROM Product";
SqlCommand comm = new SqlCommand(sql, conn);
adap = new SqlDataAdapter(comm);
DataSet ds = new DataSet();
adap.Fill(ds);
ProductID.DataTextField = ds.Tables[0].Columns["Name"].ToString();
ProductID.DataValueField = ds.Tables[0].Columns["Id"].ToString();
ProductID.DataSource = ds.Tables[0];
ProductID.DataBind();
}
protected void Page_Load(object sender, EventArgs e)
{
bindGrid();
selectList();
}
protected void btnAdd_Click(object sender, EventArgs e)
{
selectList();
sql = "INSERT INTO [Order] (CustomerID,ProductID ,EmployeeID,Quantity,Date) VALUES ('" + CustomerID.Text + "','" + ProductID.SelectedValue + "','" + EmployeeID.Text + "','" + Quantity.Text + "','" + Date.Text + "')";
conn = new SqlConnection(connstr);
conn.Open();
comm = new SqlCommand(sql, conn);
comm.ExecuteNonQuery();
conn.Close();
bindGrid();
ScriptManager.RegisterStartupScript(Page, Page.GetType(),
"myPrompt", "alert('Successfully Updated!');", true);
}
Order.aspx
Product ID:
<asp:DropDownList ID="ProductID" runat="server" CssClass="form-control" ></asp:DropDownList>
Actually, the mistake here is the page load. In 99% of ALL pages, you only want to bind and load up on the first page load. And most if not all asp controls will automatic persist for you. So, your big mistake is this:
protected void Page_Load(object sender, EventArgs e)
{
bindGrid();
selectList();
}
The above has to become this:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
bindGrid();
selectList();
}
}
In fact, you really can't build a functional web form page unless you follow the above rule. Remember, any button, any post-back, and the page load event will run again.
So yes, page load is the right place, but you in near 99% of cases need to wrap that code in the all important isPostBack = false code stub.
Once you do above, then your whole page will operate quite nice, quite normal, and in near all cases, you find the controls correct persist their values and settings.
So, no, page load is NOT too soon, and page load is VERY much the correct event and place to load up the data bound controls - but, you only want to do this on the really first page load.
In fact, there is probably 1 question near per day on SO, and their woes and problems can be fixed by following the above simple rule. Failure to note the above isPostBack? You can't really even build a working asp.net page.
Page_Load() is too late to bind your list.
Remember, when using web forms, you start from scratch and have to recreate all of your data items on every single request... even simple button click events*. This is why you call bindGrid() in the Page_Load() method. However, part of this process also involves restoring ViewState, so the button click will know what item was selected. The problem is this ViewState data is restored before the Page_Load() method is called. Therefore the grid is still empty, and the SelectedValue information you need to get from ViewState cannot be set correctly.
You can fix this by moving the code that binds your grid data up to the Init or Pre_Init events.
While I'm here, I need to reiterate my comment about SQL Injection. This is a really big deal... the kind of thing that's too important to do wrong even with learning and proof-of-concept projects. I suggest using Google to learn more about using parameterized queries with C#.
Additionally, it's rare to insert selections directly into an Orders table. Often there's a separate "ShoppingCart" table, using a Session Key for the table's primary key, where the user can build up the cart before completing the order and creating the final Order and OrderLines or OrderDetail records.
* For this reason, it's often worthwhile in web forms to do more of this work on the client browser, in javascript.
Using C# and Winform.
I read a couple of similar questions but couldn't find any great answers that could interlock with my code. So, bear with me and thank you in advance for helping me.
I have a single form that contains multiple User Controls. Inside the first user control, you can insert, update and delete records from the database. In the second User Control, there is a datagridview that is populated with all records.
The problem I have is that whenever I insert, update or delete a record inside the first user control. It won't refresh inside the datagridview when I swap to the second user control.
Beneath is the second user control that populates the datagridview
private void populate()
{
database.OpenConnection();
string query = "SELECT id, name, qoute, time, date from maintable";
SQLiteDataAdapter sda = new SQLiteDataAdapter(query, database.connection);
SQLiteCommandBuilder builder = new SQLiteCommandBuilder(sda);
var ds = new DataSet();
sda.Fill(ds);
dtgNav.DataSource = ds.Tables[0];
databas.CloseConnection();
}
private void Navigation_Load(object sender, EventArgs e)
{
populate();
dtgNav.Columns[0].HeaderText = "ID";
}
public void Refresh()
{
this.Refresh();
}
Beneath is the code for adding a record to the datagridview in the first user control
private void btnAdd_Click(object sender, EventArgs e)
{
database.OpenConnection();
string query = "INSERT INTO maintable (`id`, `name`, `qoute`, `time`,`date`) VALUES (#Id, #Name, #Qoute, #Time, #Date)";
SQLiteCommand command = new SQLiteCommand(query, database.connection);
command.Parameters.AddWithValue("#Id", tbxID.Text);
command.Parameters.AddWithValue("#Name", tbxName.Text.Trim());
command.Parameters.AddWithValue("#Qoute", tbxQoute.Text.Trim());
command.Parameters.AddWithValue("#Time", tbxTime.Text.Trim());
command.Parameters.AddWithValue("#Date", dtpDate.Value.ToString("yyyy-MM-dd"));
command.ExecuteNonQuery();
MessageBox.Show("Added new event into the database.");
database.CloseConnection();
usercontrol2.Refresh();
}
I would appreciate it if we found a way to refresh the datagridview when the button is clicked without changing the original code all too much.
You have a public void Refresh method in the second usercontrol, try modifying this.Refresh();, to say populate();. this should call your private void populate method that you called when loading which should reload the grid. Let me know if this helps.
I have a webpage called blogwebsite and in that I have a textbox and search button. I am passing the value of textbox on button click to another webform called blogseacrh through session. I also have a database bound through these webforms. In this blogsearch webpage I have taken the session variable in a textbox. Using this textbox value I am writing a oledbcommand select query. I am fetching data from the database using this textbox value and want to display it on the blogsearch webpage. For this to happen I am using oledbdatareader to read the data and then write the fetched data in the textbox. But when I am running the webpage when I click on search button it gives me the error at the oledbdatareader line saying that no given value given for one or more required parameters.
I really can't understand what I am doing wrong. Can someone please give me a solution?
This is the button click event which is working perfectly
protected void btn_srch_Click(object sender, EventArgs e)
{
Session["name"] = txt_bnm.Text;
Response.Redirect("blogseacrh.aspx");
}
This is the code that needs to be executed on another webpage on button click event
protected void Page_Load(object sender, EventArgs e)
{
if (Session["name"] != null)
{
con.Open();
txt2_bnm.Text = Session["name"].ToString();
cmd = new OleDbCommand("select user from tbl_blogs where book_name='" + txt2_bnm.text + "',con); `
OleDbDataReader d = cmd.ExecuteReader();
while (d.Read())
{
user = d["user"].ToString();
Response.Write(user);
}
cmd = new OleDbCommand("select blogs from tbl_blogs where book_name='" + txt2_bnm.Text + "' ", con);
OleDbDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
blogs = dr["blogs"].ToString();
Response.Redirect(blogs);
}
con.Close();
}
I have also checked all the field names and table name and they are all correct as well.
Can someone please solve this error. i have an assignment to complete please.
So I've got a class, commenter, and two methods within that class, SaveBtn_Click - created primarily not by me, and then also PeerReview, primarily created by me.
Anyway, the code starts off like this (after a variety of using statements):
public partial class commenter : System.Web.UI.Page
{
string employee_reviewed;
PeerReview pr = new PeerReview();
public void SaveBtn_Click(object sender, EventArgs e)
{
//all the information for the SaveBtn_Click method.
}
After that, I have PeerReview:
public void PeerReview(System.Web.UI.WebControls.ListBox listbox)
{
MySqlConnection con = new MySqlConnection("server=localhost;database=hourtracking;uid=username;password=password");
MySqlCommand cmd = new MySqlCommand("select first_name from employee where active_status=1", con);
con.Open();
MySqlDataReader r = cmd.ExecuteReader();
Console.WriteLine("Another test!");
Console.WriteLine(r);
Console.WriteLine("Hi, this is a test!");
while (r.Read())
{
listbox.Items.Add(new ListItem(Convert.ToString(r["first_name"]), Convert.ToString(r["first_name"])));
}
con.Close();
}
I'm connecting this with ASP.NET, and I can get the listbox to show up, but not the individual items in the listbox. I'm testing it with a console.writeline command, to see if that outputs anything - but nothing is being put out on the ASP page.
I'm not certain how I should reference these particular sections (new to C#, asking like 3 dozen questions about this).
ASP code looks like this:
<asp:ListBox ID="listBox1" runat="server">
You have some confused declarations.
You declare a method called PeerReview, but you also have an attempt to create an instance of PeerReview as though it were a type. I think you really just want to call the PeerReview method from your button click event, eg
public void SaveBtn_Click(object sender, EventArgs e)
{
PeerReview();
}
And then eliminate the "PeerReview pr = new PeerReview();" line. Also, as this is on a page, you have an implicit reference within the partial class to the listbox by its ID, so you don't need to pass it as a parameter. And the Console.WriteLines are not useful in a web application - you might try Response.Write if you're wanting to add that to the output for debug purposes.
Edits based on OP response
You should call PeerReview in the Page_Load event handler:
public void Page_Load(object sender, EventArgs e)
{
// You need to determine if you should call PeerReview every time the page
// loads, or only on the initial call of the page, thus determining whether
// you need the IsPostBack() test. My instinct is that you *do* want to constrain
// it to the first pass, but only you can make that determination for
// certain based on your requirements.
if (!Page.IsPostBack) //Do you need this check?
{
PeerReview();
}
}
You're trying to add items to listbox though your listBox has an id of listBox1
Rather than looping through your data and adding items why not bind the datasource to your listbox and then set the DataTextField and DataValueField on your listbox.
So for example (typos may exist..sorry.. been a while since i wrote C#)
MySqlConnection con = new MySqlConnection("server=localhost;database=hourtracking;uid=username;password=password");
MySqlCommand cmd = new MySqlCommand("select first_name from employee where active_status=1", con);
con.Open();
MySqlDataReader r = cmd.ExecuteReader();
listBox1.DataSource = r;
listBox1.DataBind();
con.Close();
If you can't bind to the reader (can't remember..) then dump your results into a datatable first, then bind to the listBox1
DataTable dTable = New DataTable();
dTable.Load(reader);
listBox1.DataSource = dTable;
listBox1.DataBind();
in your asp, set the listBox fields like:
<asp:ListBox ID="listBox1" runat="server" DataTextField="first_name" DataValueField="first_name">
quick view here is you are adding items to listbox instead of listBox1
change:
listbox.Items.Add(new ListItem(Convert.ToString(r["first_name"]), Convert.ToString(r["first_name"])));
to:
listBox1.Items.Add(new ListItem(Convert.ToString(r["first_name"]), Convert.ToString(r["first_name"])));
im working in WinForms C#.
for some reason when I want to populate my listBox it stops and says my database is corrupt.
I have added a repair line and the codes run afterwards, but nothing happends. My listbox is not populated.
Here is the code im using.:
public void button1_Click(object sender, EventArgs e)
{
SqlCeConnection cn = new SqlCeConnection(#"Data Source = Database1.mdf");
cn.Open();
SqlCeCommand cm = new SqlCeCommand("SELECT * FROM tblprojects ORDER BY Projekt_liste ASC", cn);
try
{
SqlCeDataReader dr = cm.ExecuteReader();
while (dr.Read())
{
ListBox project_list = Application.OpenForms["Form1"].Controls["tabControl1"].Controls["tabPage1"].Controls["Project_list"] as ListBox;
project_list.Items.Add(dr["Projekt_liste"].ToString());
}
cn.Close();
cn.Dispose();
}
catch (Exception ex)
{
}
}
public void button2_Click(object sender, EventArgs e)
{
SqlCeConnection cn = new SqlCeConnection();
SqlCeEngine engine = new SqlCeEngine("Data Source = Database1.mdf");
if (false == engine.Verify())
{
MessageBox.Show("Database is corrupted.");
engine.Repair(null, RepairOption.RecoverAllPossibleRows);
}
}
For example if you want to load the items
1. make sure you have a ListBox on the winform
2. name the ListBox
3. Create a ListItem
4 Add the ListItem to the ListBox
while(dr.Read())
{
ListViewItem obj=new ListViewItem(Convert.ToString(dr[0]),Convert.ToString(dr[1]);
//in object of ListViewItem give display member at first and give value member at second position
listView1.Items.Add(obj); // add object to the listbox
}
Here are a few links that you can use as well to show different ways on how to populate a ListBox
one is Windows and the other will be if you are using or plan to use ASP.NET
Populate a ListBox when using SQLDataReader
asp.net SqlDataReader example: how to use Read() method to populate ListBox
Populate ASP.NET ListBox using SqlDataReader
From Microsoft Site
The Repair method does not guarantee complete data recovery for every
database. Some forms of data corruptions cannot be repaired
completely, regardless of the Repair option that is selected by the
application.
This could be one of the case where your file is corrupted.
Also please try To have repair call straight above the call to populate Data in List.
This may help.