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Button click event doesn't work properly
I try to increment an int for each click on a default page. Int=0. It only goes up to 1. What should I do to increment the number for each click?
public partial class _Default : System.Web.UI.Page
{
private int speed = 0;
public int Speed
{
get { return speed; } // Getter
set { speed = value; } // Setter
}
public void accelerate()
{
//speed++;
this.Speed = this.Speed + 1;
}
public void decelerate()
{
// speed--;
this.Speed = this.Speed - 1;
}
public int showspeed()
{
return this.Speed;
}
//car bmw = new car();
public void Page_Load(object sender, EventArgs e)
{
//datatype objectname = new
dashboard.Text = Convert.ToString(this.showspeed());
}
public void acc_Click(object sender, EventArgs e)
{
this.accelerate();
dashboard.Text = Convert.ToString(this.showspeed());
}
public void dec_Click(object sender, EventArgs e)
{
this.decelerate();
this.showspeed();
}
}
You could use the ViewState to maintain the value across postbacks:
private int Speed
{
get
{
if (ViewState["Speed"] == null)
ViewState["Speed"] = 0;
return (int)ViewState["Speed"];
}
set { ViewState["Speed"] = value; }
}
You need to store the result in a way that will persist over postback. I suggest using ViewState, for example:
public int Speed
{
get {
if(ViewState["Speed"] == null) {
ViewState["Speed"] = 1;
}
return Convert.ToInt32(ViewState["Speed"]);
}
set {
ViewState["Speed"] = value;
}
}
Because everytime when you click on the button, it is initializing the value of speed to 0.
HTTP is stateless. That means it wil not retain the values of variable across your postback like you do in Windows Forms programming. So you need to keep the value across your postbacks.
You can use a hidden element in your page to store the value and access the value every time you want to do a function on that:
<asp:HiddenField ID="hdnFileId" runat="server" Value="" />
and in your page load, you can read the value and load it to your variable.
public void Page_Load(object sender, EventArgs e)
{
this.speed = ConvertTo.Int32(hdnFileId.Value);
}
From Adrianftode's comment, the data for the controls like TextBox, Checkbox, Radio button controls values will be posted to the server on the postback because they are rendered as standard HTML form controls in the browser. See Chapter 4. Working with ASP.NET Server Controls.
Related
Im trying to set a value in a method as shown below but when i run btnSaveValue there is no value to retrieve. Ive even tried creating a private int val in the defaul class and assigning the value to that but still a blank value comes through - can anyone help me out?
thanks
public partial class _Default : System.Web.UI.Page
{
valueAllocation valAlloc = new valueAllocation();
public void declaringValue()
{
valAlloc.setValue(5);
int testAlloc = valAlloc.getValue();
lblResult.Text="Value set here is:"+testAlloc; //THIS WORKS!!!
}
protected void btnSaveValue_Click(object sender, ImageClickEventArgs e)
{
lblResult.Text = "Value now is:" + valAlloc.getValue(); //DOESNT WORK??????!!!!!
}
}
public class valueAllocation
{
private int val;
public void setValue(int value)
{
val = value;
}
public string getValue()
{
return val;
}
}
This is because you need to save the value in each post using for example the ViewState.
This is a basic problem related with the ASP.Net page life-cycle.
Basically, every time you request your page, a new instance of the page is created on every post, and destroyed when the response returns to the client
If you want to keep the state across post backs, you need to manually save each value in the ViewState
storing the whole type in the ViewState
I think this is your best bet
Custom Type
[Serializable]
public class valueAllocation
{
public int MyValue { get; set; }
}
Code behind
protected valueAllocation MyObject
{
get
{
if(this.ViewState["c"] != null)
return (valueAllocation)this.ViewState["c"];
return null;
}
set
{
this.ViewState["c"] = value;
}
public valueAllocation declaringValue()
{
if (this.MyObject == null)
this.MyObject = new valueAllocation { MyValue = 5 };
lblResult.Text="Value set here is:"+ this.MyObject.MyValue.ToString();
return this.MyObject;
}
protected void btnSaveValue_Click(object sender, ImageClickEventArgs e)
{
declaringValue()
lblResult.Text = "Value now is:" + declaringValue().MyValue.ToString();
}
The problem is you never called decalringValue(), do this
public valueAllocation declaringValue()
{
valAlloc.setValue(5);
int testAlloc = valAlloc.getValue();
lblResult.Text="Value set here is:"+testAlloc; //THIS WORKS!!!
return valAlloc;
}
protected void btnSaveValue_Click(object sender, ImageClickEventArgs e)
{
declaringValue()
lblResult.Text = "Value now is:" + declaringValue().getValue(); //DOESNT WORK??????!!!!!
}
It is because this is web application not a desktop.You have to manage the state of page.Because on web each request is new to server.
for your scenario you have to use "viewstate" technique for maintain the state of your page.
or you have to make your variable static if you want that value is not lose.
for further details googled "State management in asp.net"
Looks like values were not set using valAlloc.setValue(SomeNumber); before calling the below method
Or I would say that valAlloc.val is having a default value of zero
protected void btnSaveValue_Click(object sender, ImageClickEventArgs e)
{
lblResult.Text = "Value now is:" + valAlloc.getValue(); //DOESNT WORK??????!!!!!
}
so you lblResult.Text is getting a zero from valAlloc.getValue()
Looks like you are looking for a static object and static linkage defined. If a global static object works for you in this case, please vote my reply up.
Suppose that, after a click on a asp:button, I'd like to store the actual "view", with selected value for each controllers, like asp:checkbox, or input inserted by users on inputbox.
Than, I change page, with a link such as "back to the previous page". I'd like so "restore" the old actual form, before leaving it.
Is it possible with .NET? Or I need to implements all controls in variables and put them in session?
There are several ways how you can persist or pass values between ASP.NET pages.
Have a look here for more informations.
Because you've mentioned that you have "tons" of controls to store and restore, i've tried to find a way to automatize this process.
Here's my approach which uses Session as storage to persist all controls' values of type IPostBackDataHandler. Not really tested but hopefully helpful anyway.
using System;
using System.Collections.Generic;
using System.Web.UI;
using System.Web.UI.WebControls;
public class FormStorage
{
private System.Web.UI.Page _page = null;
public Dictionary<String, Dictionary<String, String>> storage
{
get { return (Dictionary<String, Dictionary<String, String>>)_page.Session["FormStorage"]; }
set { _page.Session["FormStorage"] = value; }
}
public FormStorage(System.Web.UI.Page page)
{
_page = page;
initHandler();
if (this.storage == null)
{
this.storage = new Dictionary<String, Dictionary<String, String>>();
}
if(!this.storage.ContainsKey(_page.Request.Path))
this.storage.Add(_page.Request.Path, new Dictionary<String, String>());
}
private void initHandler()
{
_page.Init += Init;
_page.Load += Load;
}
private void Init(Object sender, EventArgs e)
{
loadForm();
}
private void Load(Object sender, EventArgs e)
{
saveForm();
}
private void loadForm()
{
var pageStorage = storage[_page.Request.Path];
var e = pageStorage.GetEnumerator();
while (e.MoveNext())
{
loadControl(e.Current.Key, e.Current.Value);
}
}
private void loadControl(String ID, String value)
{
Control control = findControlRecursively(_page, ID);
if (control != null)
{
setControlValue(control, value);
}
}
private void setControlValue(Control control, String value)
{
if (control is ITextControl)
{
ITextControl txt = (ITextControl)control;
txt.Text = value == null ? "" : value;
}
else if (control is ICheckBoxControl)
{
ICheckBoxControl chk = (ICheckBoxControl)control;
chk.Checked = value != null;
}
else if (control is ListControl)
{
ListControl ddl = (ListControl)control;
if (value == null)
ddl.SelectedIndex = -1;
else
ddl.SelectedValue = value;
}
}
public void saveForm()
{
saveControlRecursively(this._page);
}
private void saveControlRecursively(Control rootControl)
{
if (rootControl is IPostBackDataHandler)
{
var postBackData = _page.Request.Form[rootControl.ID];
storage[_page.Request.Path][rootControl.ID] = postBackData;
}
if (rootControl.HasControls())
foreach (Control subControl in rootControl.Controls)
saveControlRecursively(subControl);
}
private static Control findControlRecursively(Control rootControl, String idToFind)
{
if (rootControl.ID == idToFind)
return rootControl;
foreach (Control subControl in rootControl.Controls)
{
Control controlToReturn = findControlRecursively(subControl, idToFind);
if (controlToReturn != null)
{
return controlToReturn;
}
}
return null;
}
}
Here's an examplary implementation in a page that redirects to another page:
private FormStorage storage;
protected void Page_PreInit(object sender, EventArgs e)
{
storage = new FormStorage(this);
}
protected void BtnRedirect_Click(object sender, EventArgs e)
{
Response.Redirect("RedirectForm.aspx");
}
Note that it loads and saves implicitely on Page_Load/Page_PreRender. Therefor the FormStorage instance must be created in Page_PreInit.
If you want to change values after Page_Load programmatically, you need to call storage.saveForm() manually (for example in Page_PreRender) to ensure that these values are overridden, because FormStorage will auto-save all postback data in Page_Load.
Edit: The history.go approach of sh4nx0r is probably better since it's more scalable. My approach uses the Session and would not be appropriate for an internet-application with a huge amount of (possible) users.
One (small) advantage of mine is that it would work even when javascript is disabled. One larger advantage is that you can control to what page you want to redirect. You can even restore values across multiple redirects.
You don't need sessions to do this. Just make use of JavaScript.
Consider you have two pages Page1.aspx and Page2.aspx.
You have textboxes , checkboxes , radiobuttons on Page1.aspx and you have a button "Submit". By clicking the button it takes to Page2.aspx.
Just have a button "Back to Previous Page" on Page2.aspx , which on clicking takes you to Page1.aspx with all those values still being there. To do this, Add this line on your Page2.aspx page_load event
protected void Page_Load(object sender, EventArgs e)
{
btnBackButton.Attributes.Add("onClick", "javascript:window.history.go(-1);return false;");
}
In my ASP.NET page, I have a generic class that is defined as below:
public partial class log_states : BasePage
{
protected class StatesUsed
{
public int StateCode { get; set; }
public string StateName { get; set; }
}
private List<StatesUsed> _statesUsed;
}
In the Page_Load() event, I initialize _statesUsed like below, and bind it to a grid:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
_statesUsed = new List<StatesUsed>();
BindMyGrid();
}
}
private void BindMyGrid()
{
gvStates.DataSource = _statesUsed;
gvStates.DataBind();
}
I then have a form to add new States. When the user adds a state, I'm trying to add it to the local _statesUsed variable, and rebind the grid. Example:
protected void btnAddState_Click(object sender, EventArgs e)
{
_statesUsed.Add(new StatesUsed { StateCode = 1, StateName = "Test" });
BindMyGrid();
}
This always fails when trying to add the new item saying "Object reference not set to an instance of an object"...
How do I keep _statesUsed persistant? The idea is to add all user input using the generic class and then update the database at one go. If you know of another way to accomplish this, I'd be very grateful.
Thanks in advance!
Instead of
private List<StatesUsed> _statesUsed;
I'm usually using something similar to:
private List<StatesUsed> _statesUsed
{
get
{
var result = ViewState["_stateUsed"] as List<StatesUsed>;
if ( result == null )
{
result = new List<StatesUsed>();
ViewState["_stateUsed"] = result;
}
return result;
}
}
I.e. I am persisting page class variables to the ViewState.
If you want to keep stuff "alive" through multiple postbacks you either have to store stuff to a database, use Session, use the Viewstate, or store it temporarily in shared server memory. Which of these you choose is dependent on your use case,
In your case I would probably add an asp:HiddenField runat="server" ID="HiddenFieldUsedStateIDs" in which I wrote the IDs comma separated whenever there is a change and then read the values into the generic list in Page_Load (on every Page_Load, not just !IsPostBack)
This would utilize the Viewstate mechanism in Asp.Net to write the values to the rendered HTML and read it back into the HiddenField's value on each post
Asuuming that your viewstate in not disabled, you could do,
protected void btnAddMat_Click(object sender, EventArgs e)
{
List<StatesUsed> temp = null;
temp = (List<StatesUsed>)gvStates.DataSource;
if(temp != null)
temp.Add(new StatesUsed { StateCode = 1, StateName = "Test" });
gvStates.DataBind();
}
I once asked for a way to let a linkbutton pass more than one value in the commandArgument and then I reached the approach where I pass a string of multiple values separated by any character and split it into it's original parts...that didn't work out I don't know what was wrong with the splitting!
Now I tried the only solution I got, which is created a user control of the LinkButton and add properties to accept any values nedeed!...could you please tell me what's wrong with my 2 approaches and which is better ?
The first question can be found here : link text
and this is the code for the user control approach >>
MultivaluedLinkButton.ascx :
<asp:LinkButton ID="LnkBtnSort" runat="server" Text="Sort" OnClick="LnkBtnSort_Clicked"/>
MultivaluedLinkButton.ascx.cs :
public partial class MultivaluedLinkButton : System.Web.UI.UserControl
{
public event EventHandler Click;
private int _sortingType;
private string _sortingFactor;
private string _text;
public int SortingType
{
set { _sortingType = value; }
get { return _sortingType; }
}
public string SortingFactor
{
set { _sortingFactor = value; }
get { return _sortingFactor.ToString(); }
}
//public string Text
//{
// set { _text = value; }
// get { return _text.ToString(); }
//}
protected void LnkBtnSort_Clicked(object sender, EventArgs e)
{
if( Click != null )
{
this.Click(this, EventArgs.Empty);
}
}
}
Finally, Here's the implementation of my control inside an aspx page:
protected void MultivaluedLinkButton1_Clicked(object sender, EventArgs e)
{
MultivaluedLinkButton ctrl = (MultivaluedLinkButton)sender;
using (SqlConnection cn1 = new SqlConnection(ConfigurationManager.ConnectionStrings["testConnectionString"].ConnectionString))
{
using (SqlCommand cm1 = new SqlCommand(commandString2, cn1))
{
cm1.Parameters.Add("#arrange_by_id", System.Data.SqlDbType.Int);
cm1.Parameters["#arrange_by_id"].Value = ctrl.SortingType;
cn1.Open();
using (SqlDataReader dr1 = cm1.ExecuteReader())
{
SortBy_rpt.DataSource = dr1;
SortBy_rpt.DataBind();
}
}
}
}
The item template of the repeater in the implementation page :
<ItemTemplate>
<uc1:MultivaluedLinkButton ID="MultivaluedLinkButton1" runat="server" OnClick="MultivaluedLinkButton1_Clicked" SortingType='<%#Eval("arrange_by_id")%>' />
</ItemTemplate>
The problem i see is, you have an eventHandler in your usercontrol which you never really use.
Not 100% sure but, on the Page_Load of your parent page, you need to add MultivaluedLinkButton1_Clicked event to your handler.
MultivaluedLinkButton1.EventHandler_Click = new EventHandler(this.MultivaluedLinkButton1_Clicked);
MultivaluedLinkButton1.LnkBtnSort.Click = MultivaluedLinkButton1.EventHandler_Click;
Basically you are telling that when a user clicks on your linkbutton, MultivaluedLinkButton1_Clicked() on the parent page should be called.
You can remove OnClick="MultivaluedLinkButton1_Clicked" from your UserControl properties on your parent page.
Can I assign a value to a variable (int) and never lose this value inside any scope ?
the problem is I am assigning the value to the variable in some scopes but the variable returns to its default value (zero) in other scopes..
Example :
protected void Button_AddNewCourse_Click(object sender, EventArgs e)
{
ID = 10;
}
so when I am trying to use ID in other functions it falls back to zero
protected void AnotherFunction(object sender, EventArgs e)
{
// Variable ID here is zero
}
At a guess, perhaps you're a newcomer to ASP.NET and haven't figured out why page-level variables don't keep their state between postbacks. Try reading up on Session state and Viewstate
Or for a general overview: ASP.NET State Management Overview
e.g. based on your code example, you could use a Session entry to store the value:
protected void Button_AddNewCourse_Click(object sender, EventArgs e)
{
Session["ID"] = 10;
}
protected void AnotherFunction(object sender, EventArgs e)
{
int tempID = (int)Session["ID"];
}
There's lots of other things you could also do - use Viewstate, for example.
Change the line that looks similar to this (which is probably somewhere):
public int ID { get; set;}
to something like
// keep the value of ID in this page only
public int ID { get { return (int)ViewState["ID"]; } set { ViewState["ID"] = value; } }
or
// keep the value of ID in every page
public int ID { get { return (int)Session["ID"]; } set { Session["ID"] = value; } }
Maybe try using readonly variables?