Why am I losing object references on the postback? - asp.net

I am developing an asp.net (3.5) application and I am puzzled with the behavior of the postbacks.
Consider the following scenario: I have a web user control that is basically a form. However each form field is a web user control in itself.
In the click event of the save button I iterate through all controls in my form and I retrieve the field value and the field name that refers to the database field that I am saving the value to.
The click event triggers a postback and it is during the postback that I visit the controls and here is the funny thing: the property value for the database field has become null! Could anyone shed a light here?
Here is some basic code:
[Serializable]
public partial class UserProfileForm : CustomIntranetWebappUserControl
{
protected override void OnInit(EventArgs e)
{
//AutoEventWireup is set to false
Load += Page_Load;
CancelLinkButton.Click += CancelButtonClickEvent;
SaveLinkButton.Click += SaveButtonClickEvent;
base.OnInit(e);
}
private void SaveButtonClickEvent(object sender, EventArgs e)
{
VisitFormFields();
}
private void VisitFormFields()
{
var userProfileVisitor = new UserProfileVisitor();
foreach (var control in Controls)
{
if (control is FormFieldUserControl)
{
var formField = (FormFieldUserControl) control;
formField.Visit(userProfileVisitor);
}
}
userProfileVisitor.Save();
}
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
BindText();
}
}
private void BindText()
{
LastNameFormLine.LabelText = string.Format("{0}:", HomePage.Localize("Last Name"));
LastNameFormLine.InputValue = UserProfile.LastName;
LastNameFormLine.IsMandatoryField = true;
LastNameFormLine.IsMultilineField = false;
LastNameFormLine.ProfileField = "UserProfile.LastName";
//... the rest of this method is exactly like the 4 lines above.
}
}
[Serializable]
public abstract class FormFieldUserControl : CustomIntranetWebappUserControl
{
public string ProfileField { get; set; }
public abstract void Visit(UserProfileVisitor userProfileVisitor);
}
[Serializable]
public partial class FormLineTextBox : FormFieldUserControl
{
//... irrelevant code removed...
public override void Visit(UserProfileVisitor userProfileVisitor)
{
if (userProfileVisitor == null)
{
Log.Error("UserProfileVisitor not defined for the field: " + ProfileField);
return;
}
userProfileVisitor.Visit(this);
}
}
[Serializable]
public class UserProfileVisitor
{
public void Visit(FormLineTextBox formLine)
{
// The value of formLine.ProfileField is null!!!
Log.Debug(string.Format("Saving form field type {1} with profile field [{0}] and value {2}", formLine.ProfileField, formLine.GetType().Name, formLine.InputValue));
}
// ... removing irrelevant code...
public void Save()
{
Log.Debug("Triggering the save operation...");
}
}

Remember ASP.NET is stateless. Any properties created are destroyed after the page has been render to the browser. So you have to recreate objects on each post back or store them in View, Session, or Application State.
When you do a property you have to tell it to save the view state it does not do it automatically. Here is a sample of a view state property.
public string SomePropertyAsString
{
get
{
if (this.ViewState["SomePropertyAsString"] == null)
return string.Empty;
return (string)this.ViewState["SomePropertyAsString"];
}
set { this.ViewState["SomePropertyAsString"] = value; }
}
public MyCustomType ObjectProperty
{
get
{
if (this.ViewState["ObjectProperty"] == null)
return null;
return (MyCustomType)this.ViewState["ObjectProperty"];
}
set { this.ViewState["ObjectProperty"] = value; }
}

First guess would be that BindText() shouldn't be in Page_Load, but in Page_Init, so the control state will be saved.

#David Basarab, this is not true afaik, and was only the case in .Net 1.1, in .Net2 and up this is all handled by the framework if you do all the magic stuff in the Init.

Your problem is that 'ProfileField' isn't available on the Postback, right?
The solution is to store the value for that in ViewState (instead of an auto-implemented property). Without that, it won't be available on the postback.

Related

Xamarin Forms check is page is Modal

So basically I'm try to to find out if a page was pushed modally.
Here is the code I have for my extension method:
public static bool IsModal(this Page page)
{
return page.Navigation.ModalStack.Any(p => page == p);
}
The issue is; p never equals page due to the fact p changes to NavigationPage during runtime although intellisense reports it as a type of Page at compile time.
I've tried casting p to a Page but the type does not change at runtime and intellisense just moans that the cast is redundant.
I call this extension by using CurrentPage.IsModal in my View Model. CurrentPage is a type of Page at compile time but then changes to NavigationPage at runtime.
The confusing thing is that during debugging, p has properties such as CurrentPage and RootPage which show in the debugger, but these are not accessible by using p.CurrentPage as the compiler complains they don't exist !?! I was going to try an compare these but I can't access them but can view them in the debugger.
You need to check the type of page first, a page without navigationbar can also be pushed modally:
public partial class MainPage : ContentPage
{
public MainPage()
{
InitializeComponent();
}
private async void Button_Clicked(object sender, EventArgs e)
{
Page1 p = new Page1();
await this.Navigation.PushModalAsync(p, true);
bool b = PageExtensions.IsModal(p);
Console.WriteLine(b);
}
}
public static class PageExtensions
{
public static bool IsModal(this Page page)
{
if (page.GetType() == typeof(NavigationPage))
{
return page.Navigation.ModalStack.Any(p => ((NavigationPage)p).CurrentPage.Equals(page));
}
else
{
return page.Navigation.ModalStack.Any(p => p.Equals(page));
}
}
}
So this code works:
public static class PageExtensions
{
public static bool IsModal(this Page page)
{
return page.Navigation.ModalStack.Any(p=> ((NavigationPage) p).CurrentPage.Equals(page));
}
}
I'm concerned that is not safe as it assumes p is a Type of NavigationPage.
Can you try this, there could be typos, I wrote this freehand
public static bool IsModal(this Page page)
{
if (page.Navigation.ModalStack.Count > 0)
{
foreach (var thisPage in page.Navigation.ModalStack)
{
if (thisPage.Equals(page))
return true;
}
return false;
}
else
return false;
}
This is what I made to check the last pushed modal. Hope it helps to someone.
public async Task NewModalPagePushAsync(Page pageToOpen)
{
var lastModalPage = Application.Current.MainPage.Navigation.ModalStack;
if (lastModalPage.Count >= 1)
{
if (lastModalPage.Last().GetType().Name == pageToOpen.GetType().Name)
return;
}
await Application.Current.MainPage.Navigation.PushModalAsync(pageToOpen);
}

When does HttpContext.AllErrors contain more than one exception?

In an ASP.NET application typical error handling code involves some variation of GetLastError(), however there's also HttpContext.AllErrors collection of which the GetLastError() method only retrieves the first one. What are the scenarios where the AllErrors collection might contain more than 1 exception? I cannot think of anything, but obviously it's there for a purpose...
The ASP.NET Framework supports a different model where a request can encounter multiple errors, all of which can be reported without stopping request processing, allowing for more nuanced and useful information to be presented to the user.
namespace ErrorHandling
{
// sample class adding errors to HttpContext
public partial class SumControl : System.Web.UI.UserControl
{
protected void Page_Load(object sender, EventArgs e)
{
if (IsPostBack)
{
int? first = GetIntValue("first");
int? second = GetIntValue("second");
if (first.HasValue && second.HasValue)
{
//result.InnerText = (first.Value + second.Value).ToString();
//resultPlaceholder.Visible = true;
}
else
{
Context.AddError(new Exception("Cannot perform calculation"));
}
}
}
private int? GetIntValue(string name)
{
int value;
if (Request[name] == null)
{
Context.AddError(new ArgumentNullException(name));
return null;
}
else if (!int.TryParse(Request[name], out value))
{
Context.AddError(new ArgumentOutOfRangeException(name));
return null;
}
return value;
}
}
}
// intercepting the errors
public class Global : System.Web.HttpApplication
{
protected void Application_EndRequest(object sender, EventArgs e)
{
if (Context.AllErrors != null && Context.AllErrors.Length > 1)
{
Response.ClearHeaders();
Response.ClearContent();
Response.StatusCode = 200;
Server.Execute("/MultipleErrors.aspx");
Context.ClearError();
}
}
}
// MultipleErrors code behind
public partial class MultipleErrors : System.Web.UI.Page
{
public IEnumerable<string> GetErrorMessages()
{
return Context.AllErrors.Select(e => e.Message);
}
}
The answer is heavily referencing pro asp.net 4.5 from appress

User Control's child controls not getting instantiated

public partial class ChatUserControl : System.Web.UI.UserControl
{
UserChatClass ucc = new UserChatClass();
public ChatUserControl()
{
lblChatFriend = new Label();
txtChatMessage = new TextBox();
imgFriend = new Image();
rpChatMessages = new Repeater();
}
public string ChatFriend { get { return this.lblChatFriend.Text; } set { this.lblChatFriend.Text = value; } }
public string imgFriendUrl { get { return this.imgFriend.ImageUrl; } set { this.imgFriend.ImageUrl = value; } }
public object rpChatDataSource { get { return this.rpChatMessages.DataSource; } set { this.rpChatMessages.DataSource = value; } }
public Repeater rpChatMessagesToBind { get { return this.rpChatMessages; } set { this.rpChatMessages = value; } }
}
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
ChatUserControl user1 = new ChatUserControl();
divChatUserControlCover.Controls.Add(user1);
}
}
private void BindUserControls()
{ ChatUserControl user1 = divChatUserControlCover.Controls[1] as ChatUserControl;
user1.ChatFriend = row["username"].ToString();
user1.imgFriendUrl = "../../HttpImageHandler.jpg?username=" + row["username"].ToString();
DataSet dsCM = ucc.GetChatMessages(Session["username"].ToString(), row["username"].ToString());
user1.rpChatDataSource = dsCM;
user1.DataBindForRpChatMessagesToBind();
user1.Visible = true;
}
Master.aspx
<div id="divChatUserControlCover" runat="server">
</div>
Ok I have edited the code and now I have created properties. How do I call the DataBind method for rpChatMessages? I also cant see my usercontrol on page. Why
I'm not sure if your trying to reference the first label or second label. If its the second lable you can't just do chatMessage. you would have to do
((Label)rpChatMessages.FindControl("chatMessage")) due to scope of controls.
When you reference a component inside another component (ie Repeater) the child component no longer belongs to the document (implied this) but rather belongs to the control, ie
this.rpChatMessages { chatMessage }
I think you are just trying to pass a value to one control inside a UserControl if this is correct, declare a public property like this:
ASCX code behind
public string MyProperty
{
get
{
return this.lbl.Text;
}
set
{
this.lbl.Text = value;
}
}
Setting the value to the UserControl
private void BindUserControls()
{
ChatUserControl user1 = divChatUserControlCover.Controls[1] as ChatUserControl;
user1.MyProperty = row["username"].ToString();
Setting the value in the page markup
<uc1:ChatUserControl MyProperty='<%# Eval("some field") %>' ...
Edit 1
Remove that line
public object rpChatDataSource { get { return this.rpChatMessages.DataSource; } set { this.rpChatMessages.DataSource = value; }
And instead add a method
public void BindMyRepeaterOrWhatever(IEnumerable<Yourentity> data)
{
this.myDataBoundControl.DataSource = data;
this.myDataBoundControl.DataBind();
}
You can change the IEnumerable<Yourentity> data for object data but if you can pass a strongly typed enumeration would be better
To my surprise I found why my user control's child controls dont get instantiated. Its because ChatUserControl user1 = new ChatUserControl() doesnt get its child controls initialized.
The proper way to create a new intance of user control is this way....
ChatUserControl user1 = (ChatUserControl)Page.LoadControl("~/ChatUserControl.ascx");

ASP.NET custom controls - custom property doesn't hold the assigned value on postaback

I have a custom asp-net control that inherits from another one and its works as expected, though the properties are only set properly if i code them in the markup directly, so for instance if i need set a property at runtime that is some dynamic value, this value is never set or somehow lost.
Here's the markup code:
<!--related form-->
<fw:advancedformdisplay id="formDisp" runat="server" captchaenabled="true" EmailEnabled="true" EnableViewState="true" captchaprivatekey="xxxxxxxxxxxxxxxxxxxx" captchapublickey="xxxxxxxxxxxxx" captchatheme="white" SourceType="MenuItem" SourceMainId="Auto">
</fw:advancedformdisplay>
This is the code of the control:
[DefaultProperty("CaptchaEnabled"),ToolboxData("<{0}:AdvancedFormDisplay runat=server></{0}:AdvancedFormDisplay>"), Description("This is an enhanced FormDisplay control that inlcudes Googles Captcha control is enabled")]
public class AdvancedFormDisplay :SiteBuilder.WebControls.FormDisplay
{
bool _CaptchaEnabled = false, sendEmail = false;
string captchaErrorMessage = "The verification code entered is not valid. Please try again!";
RecaptchaControl captchaControl = null;
string captchaPrivateKey = "", captchaPublicKey = "", captchaTheme = "clean";
string originalFormHtml = string.Empty;
string afterText = string.Empty, beforeText = string.Empty;
Literal litHtmlForm = null;
string captchaErrorClass = "errorCaptcha";
public string EmailBeforeText
{
get { return beforeText; }
set { beforeText = value; }
}
public string EmailAfterText
{
get { return afterText; }
set { afterText = value; }
}
public string CaptchaErrorClass
{
get { return captchaErrorClass; }
set { captchaErrorClass = value; }
}
public bool CaptchaEnabled
{
get { return _CaptchaEnabled; }
set { _CaptchaEnabled = value; }
}
public bool EmailEnabled
{
get { return sendEmail; }
set { sendEmail = value; }
}
public string CaptchaErrorMessage
{
get { return captchaErrorMessage; }
set { captchaErrorMessage = value; }
}
/// <summary>
/// red,white,blackglass,clean
/// </summary>
public string CaptchaTheme
{
get { return captchaTheme; }
set { captchaTheme = value; }
}
public string CaptchaPrivateKey
{
get { return captchaPrivateKey; }
set { captchaPrivateKey = value; }
}
public string CaptchaPublicKey
{
get { return captchaPublicKey; }
set { captchaPublicKey = value; }
}
protected override void OnLoad(EventArgs e)
{
base.OnLoad(e);
}
public override void OnSaved(FormDisplayEventArgs e)
{
//If captcha control is enabled we need to adda bit of code to redirect form properly
if (CaptchaEnabled && e.Redirect && !e.SendMail)
{
//Do Stuff
}
if(sendEmail)
{
//Send email
}
base.OnSaved(e);
}
public override void OnSaving(FormDisplayEventArgs e)
{
if (CaptchaEnabled)
{
//Validate and do stuff
}
base.OnSaving(e);
}
}
And then in my asp.net page that is using control, created by markup code, in the Page_Load() i try to assign some values to some properties and and the values aren't set properly, meaning that if i have set for isntance, the property EmailBeforeText = "somthing" this value will not be assigned..
protected void Page_Load(object sender, EventArgs e)
{
//2: Get the language of menuitem - Based on current culture setting (for by dropdownbox - change logic)
try
{
currentCulture = Thread.CurrentThread.CurrentCulture.ToString();
// Redirect if domain does not match rootnode.
DomainChecker.CheckURL(this.Request, this.Response, currentCulture);
if (footerArticle != null)
footerArticle.SourceMenuId = Digimaker.Config.Custom.Get("FooterID_" + currentCulture).ToString();
}
catch
{
currentCulture = "en-GB";
if( footerArticle != null )
footerArticle.SourceMenuId = Digimaker.Config.Custom.Get("FooterID_" + currentCulture).ToString();
}
Any ideas what i'm missing here?
Thanks a lot for your reading!
Regards,
byte_slave
short answer: use viewstate to persist your custom values!
Understanding ASP.NET ViewState whitepaper (see example with NavigateUrl)
edit: as reading the white-paper is obviously a really hard thing:
Each control is responsible for storing its own state, which is
accomplished by adding its changed state to its ViewState property.
The ViewState property is defined in the System.Web.UI.Control class,
meaning that all ASP.NET server controls have this property available.
(When talking about view state in general I'll use lower case letters
with a space between view and state; when discussing the ViewState
property, I'll use the correct casing and code-formatted text.)
If you examine the simple properties of any ASP.NET server control
you'll see that the properties read and write directly to the view
state. (You can view the decompiled source code for a .NET assembly by
using a tool like Reflector.) For example, consider the HyperLink Web
control's NavigateUrl property. The code for this property looks like
so:
public string NavigateUrl
{
get
{
string text = (string) ViewState["NavigateUrl"];
if (text != null)
return text;
else
return string.Empty;
}
set
{
ViewState["NavigateUrl"] = value;
}
}
As this code sample illustrates, whenever a control's property is
read, the control's ViewState is consulted. If there is not an entry
in the ViewState, then the default value for the property is returned.
When the property is assigned, the assigned value is written directly
to the ViewState.

Unable to hook into PropertyChanged event using MVVM-Light

Greetings, creating my first MVVM based WPF app and trying to figure out why I'm unable to hook into the PropertyChanged event of a dependency property.
Code in the parent view model:
void createClients()
{
var clients = from client in Repository.GetClients()
select new ClientViewModel(Repository, client);
foreach (var client in clients)
{
client.PropertyChanged += onClientPropertyChanged;
}
Clients = new ViewableCollection<ClientViewModel>(clients);
Clients.CollectionChanged += onClientsCollectionChanged;
}
// Never gets called
void onClientPropertyChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == "Name")
{
//...
}
}
ViewableCollection is a simple extension of ObservableCollection to encapsulate a View.
In the ClientViewModel the setters are being called but RaisePropertyChanged isn't working as I would expect, because onClientPropertyChanged isn't being invoked. Both view models inherit from ViewModelBase.
public string Name
{
get { return client.Name; }
set
{
if (value == client.Name) return;
client.Name = value;
RaisePropertyChanged("Name");
}
}
If I wire up PropertyChanged to a method inside the ClientViewModel then it is being fired, so I'm stumped as to why this isn't working in the parent view model. Where am I going wrong?
This SO question explains the problem; ObservableCollection protects the PropertyChanged event.
One solution is to use MVVM-Light Messenger:
void createClients()
{
var clients = from client in Repository.GetClients()
select new ClientViewModel(Repository, client);
Clients = new ViewableCollection<ClientViewModel>(clients);
Clients.CollectionChanged += onClientsCollectionChanged;
Messenger.Default.Register<PropertyChangedMessage<string>>(this, (pcm) =>
{
var clientVM = pcm.Sender as ClientViewModel;
if (clientVM != null && pcm.PropertyName == "Name")
{
// ...
}
});
}
createClients() should be refactored, but for consistency with the question code I'll leave it in there. Then a slight change to the property setter:
public string Name
{
get { return client.Name; }
set
{
if (value == client.Name) return;
string oldValue = client.Name;
client.Name = value;
RaisePropertyChanged<string>("Name", oldValue, value, true);
}
}

Resources