Develop Reference

Navigation Helper SaveState / LoadState works incorrect

First, I read a list of entries from a database and display it in a ListView. When I leave the page to show details of an entry, then go back to the list, everything is ok.
Next, I open another page to add one entry to the database.
Go back to the list, reading from database shows me the correct count.
When I go to display one detail, the correct count is stored in SaveState.
Go back to the list, LoadState give the wrong count. It's the former state.
Display other details and go back now works with the old list and do not show me the added entry.
This is my code:
private void getList()
{
memoList = new List<MemoItem>();
db.loadHistory(ref memoList);
DelButton.IsEnabled = false;
System.Diagnostics.Debug.WriteLine("GetList, memoList[{0}]", memoList.Count);
}
private void NavigationHelper_SaveState(object sender, SaveStateEventArgs e)
{
if (memoList != null)
{
e.PageState["MemoItem"] = memoList;
if (memoSelected > -1)
e.PageState["memoSelected"] = memoSelected;
System.Diagnostics.Debug.WriteLine("SaveState, memoList[{0}]", memoList.Count);
}
}
private void NavigationHelper_LoadState(object sender, LoadStateEventArgs e)
{
if (e.PageState != null)
{
if (e.PageState.ContainsKey("MemoItem"))
{
memoList = (List<MemoItem>)e.PageState["MemoItem"];
System.Diagnostics.Debug.WriteLine("LoadState, memoList[{0}]", memoList.Count);
if (e.PageState.ContainsKey("memoSelected"))
memoSelected = (int)e.PageState["memoSelected"];
MemoListView.ItemsSource = memoList;
MemoListView.Visibility = Visibility.Visible;
}
else
{
getList();
showList();
}
}
}
Here are the Systems.Diagnostic outputs with comments in ():
GetList, memoList[8] (first time loaded)
SaveState, memoList[8] (leave the list to display details for one entry)
LoadState, memoList[8] (come back to the ListView)
SaveState, memoList[8] (leave the list to another page and add one entry)
GetList, memoList[9] (back to the list, read the correct entry count from database)
SaveState, memoList[9] (leave the ListView to display details for one entry)
LoadState, memoList[8] (come back to the ListView loads the wrong old list)
SaveState, memoList[8] (and works with the old list...)
LoadState, memoList[8] (...)
Remark: I can't call GetList from database every time, because I have to preserve checkmarks in the list which are not contained in the database.
What is wrong in my code? How can I resolve this problem? How to invalidate the StateEvent data after availability of a new list from database?

The problem is solved now. It was actually a consequence of the back stack manipulation.
I have four basic pages in my program, for which a GoBack makes sense. But I do not want to go back deeper. (I do not think anyone wants to go back 20 or more steps, but the seemingly unlimited BackStack would allow that.The required memory consumption is not negligible.)
In order to clear the BackStack at selecting one of the basic pages, I had this:
private void NavButton_Click(object sender, RoutedEventArgs e)
{
Button b = sender as Button;
if (b != null && b.Tag != null)
{
Type pageType = Type.GetType(b.Tag.ToString());
if (pageType != null)
{
if (rootFrame.CurrentSourcePageType != pageType)
{
rootFrame.Navigate(pageType, rootFrame);
// No goBack for Basic Pages
if (testBasicPage(pageType))
{
while (rootFrame.BackStackDepth > 1)
{
rootFrame.BackStack.RemoveAt(0);
}
}
}
}
}
}
That worked fine until I came across the problem with SaveState / Load State.
Now I first empty the BackStack and then navigate to the target page. That works.
private void NavButton_Click(object sender, RoutedEventArgs e)
{
Button b = sender as Button;
if (b != null && b.Tag != null)
{
Type pageType = Type.GetType(b.Tag.ToString());
if (pageType != null)
{
if (rootFrame.CurrentSourcePageType != pageType)
{
// No goBack for Basic Pages
if (testBasicPage(pageType))
{
while (rootFrame.BackStackDepth > 0)
{
rootFrame.BackStack.RemoveAt(0);
}
}
rootFrame.Navigate(pageType, rootFrame);
}
}
}
}

Identify during Page.Load if Button click event is going to be handled

I have ASPX web page which has a Button on it. Once user click this button, request is submitted to server and button click event handler is executed.
I have some logic that must reside on Page.Load, but this logic depends if request has been submitted by button click. Based on page life cycle event handlers executes after Page Load.
Question: How in Page load I can find out what event handlers are going to be executed after Page Load?

#akton's answer is probably what you SHOULD do, but in case you want to go off the reservation and determine what is causing a postback early on in the lifecycle, you can interrogate the postback data to determine what was clicked. This will NOT give you what actual functions/handlers will be executed during event handling, however.
First, if something other than a Button/ImageButton caused the postback, the ID of the control will be in __EVENTTARGET. If a Button caused the postback, there is something "cute" ASP.NET does: it ignores all other buttons so that only the clicked button shows up on the form. An ImageButton is a little different, because it will send coordinates. A utility function you can include:
public static Control GetPostBackControl(Page page)
{
Control postbackControlInstance = null;
string postbackControlName = page.Request.Params.Get("__EVENTTARGET");
if (postbackControlName != null && postbackControlName != string.Empty)
{
postbackControlInstance = page.FindControl(postbackControlName);
}
else
{
// handle the Button control postbacks
for (int i = 0; i < page.Request.Form.Keys.Count; i++)
{
postbackControlInstance = page.FindControl(page.Request.Form.Keys[i]);
if (postbackControlInstance is System.Web.UI.WebControls.Button)
{
return postbackControlInstance;
}
}
}
// handle the ImageButton postbacks
if (postbackControlInstance == null)
{
for (int i = 0; i < page.Request.Form.Count; i++)
{
if ( (page.Request.Form.Keys[i].EndsWith(".x")) || (page.Request.Form.Keys[i].EndsWith(".y")))
{
postbackControlInstance = page.FindControl(page.Request.Form.Keys[i].Substring(0, page.Request.Form.Keys[i].Length-2) );
return postbackControlInstance;
}
}
}
return postbackControlInstance;
}
All that being said, if you can refactor your control/page to delay execution, your code will be much cleaner/more robust if you use the paradigm suggested by #akton.

There may be a better solution to the problem. Do you want the code to only run when the page is first loaded and you are using postbacks? If so check the Page.IsPostBack property. If the code does not need to run before other event handlers, move it to OnPreRender because it fires after event handlers.

These helped me a lot: I wanted to save values from my gridview, and it was reloading my gridview /overriding my new values, as i have IsPostBack inside my PageLoad.
if (HttpContext.Current.Request["MYCLICKEDBUTTONID"] == null)
{ //Do not reload the gridview.
}
else { reload my gridview. }
SOURCE: http://bytes.com/topic/asp-net/answers/312809-please-help-how-identify-button-clicked

Accessing a dynamic RadioButtonList array object

I've created an array of RadioButtonList class, but apparently can't seem to access it or use the answer retrieved from it. I always get the exception: Object reference not set to an instance of an object
static int jimmy = 0;
protected void Button5_Click(object sender, EventArgs e)
{
int sizeOfPain = GlobalVariables.sympLCWR1Pain.Count;
RadioButtonList[] RBLPain = new RadioButtonList[sizeOfPain];
Label1.Visible = false;
RadioButtonList1.Visible = false;
Label[] Labella = new Label[sizeOfPain];
if (jimmy < sizeOfPain)
{
Labella[jimmy] = new Label();
RBLPain[jimmy] = new RadioButtonList();
Labella[jimmy].Text = GlobalVariables.sympLCWR1Pain[jimmy];
RBLPain[jimmy].Items.Add("Yes");
RBLPain[jimmy].Items.Add("No");
Panel1.Controls.Add(Labella[jimmy]);
Panel1.Controls.Add(RBLPain[jimmy]);
if (RBLPain[jimmy].SelectedIndex == 0)
{
GlobalVariables.sympLCWR1Yes.Add(GlobalVariables.sympLCWR1Pain[jimmy]);
}
}
else
{
Label2.Text = "YOUS DONE!";
Label3.Text = GlobalVariables.sympLCWR1Yes[0];
Button5.Visible = false;
}
jimmy++;
}
i get the exception at the if condition. Any help would be appreciated thanks :)

What that error means is that you are trying to access something that hasn't yet been instantiated. In your updated code, I see you have the following within your click event handler:
RadioButtonList[] RBLPain = new RadioButtonList[sizeOfPain];
Label[] Labella = new Label[sizeOfPain];
This means that every time the click event is handled, you are redeclaring the RBLPain and Labella arrays. Also, when execution leaves leaves the handler, the variables fall out of scope, so you will not be able to use them in other functions, or use the changes made within the handler from one call to the next. I don't know what the rest of your code is doing, but despite the seemingly unnecessary arrays, execution should survive your click event.
In your original post you were trying to access the SelectedItem.Text property of the RBLPain[jimmy]. In this revision you are checking the SelectedIndex instead. When SelectedIndex is -1, SelectedItem will be null, perhaps this led to your original problem. Regardless of what is changed on your form, because you are creating a new RadioButtonList during every click event, you are not working with the values from your form - SelectedIndex will always be -1 from what I can see.

I dont understand why you checking the condition .If you are creating rbl on buttonclick first item should always get selected. Anyway use RBLPain[jimmy].SelectedIndex=0;before if condition.

Can you clear Page.Request.QueryString?

My problem is as follows:
I am adding a variable to the URL that should trigger a search when the page loads, depending on what is in the variable. If you navigate to that same page without the variable then it shouldn't do anything special on page load. I figured that the following would do the trick:
protected void Page_Load(object sender, EventArgs e)
{
if (Page.Request.QueryString["cell"] != null)
{
txtCell.Text = Page.Request.QueryString["cell"];
Lookup_Cell(Page.Request.QueryString["cell"]);
//BUGGED, this keeps running when i try a new search
//Page.Request.QueryString["cell"] = null;
}else{
//do nothing, empty string
}
}
This worked like a charm, but i have a search button of the form that is supposed to call the Lookup_Cell method for a cell you specify in a TextBox. i need to make Page.Request.QueryString empty so next time the page loads it won't fire this special OnLoad. I tried:
Page.Request.QueryString["cell"] = null;
but that didn't work. I looked for other methods, but can't find a definite answer.

You can make a simple PostBack check and when there is a post back, get the string from your text box.
string cFinalQueryString = "";
if(!IsPostBack)
{
if (Page.Request.QueryString["cell"] != null)
{
cFinalQueryString = Page.Request.QueryString["cell"];
}else{
//do nothing, empty string
}
}
else
{
cFinalQueryString = txtCell.Text;
}
txtCell.Text = cFinalQueryString;
Lookup_Cell(cFinalQueryString);
Or alternative, when you have post back, redirect to new page with new 'cell' query
if(IsPostBack && Page.Request.QueryString["cell"] != txtCell.Text)
{
Responce.Redirect("CurrentPage.aspx?cell=" + UrlEncode(txtCell.Text), true);
return ;
}

The querystring is sent by the browser with each request to that URL.
It sounds like you want to redirect to a URL without a querystring.

files in C# - "file is used by another process"

I have following code:
private void askforlocation()
{
if (File.Exists("location.txt"))
{
System.IO.StreamReader loc = new System.IO.StreamReader("location.txt");
string loca = loc.ReadToEnd();
if (loca != "")
{
int index = comboBox1.FindString(loca);
comboBox1.SelectedIndex = index;
}
else
{
label6.Text = "Please select the location!";
}
loc.Close();
}
else label6.Text = "Please select the location!";
}
It is supposed to read value "location" from the file and put it to the combo box, which works ok.
I run this script on Form1_Load.
Now, I have another script:
private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
string value = comboBox1.SelectedItem.ToString();
System.IO.File.WriteAllText("location.txt", value);
}
This one is supposed to record the choice so that user doesn't need to enter location every time.
What is happening is when I start a program, so the value is already set, then I try to change it (so that theoretically it should overwrite the previous one), but I get an exception, saying that file is already being used by another process.
I do close the file after I used it. I also tried FILE.DISPOSE.
What am I doing wrong?

I think what's happening here is that this code:
if (loca != "")
{
int index = comboBox1.FindString(loca);
comboBox1.SelectedIndex = index;
}
is causing the SelectedIndexChanged event to be raised on the combobox. When that event is raised, comboBox1_SelectedIndexChanged is called, and that method again tries to access location.txt.
To fix, I would first change the code in askforlocation to something like this:
if (File.Exists("location.txt"))
{
var loca = string.Emtpy;
using(var loc = new System.IO.StreamReader("location.txt"))
{
loca = loc.ReadToEnd();
}
....
}
since there's no need to keep the file open for longer than necessary (note that the using block will call the Dispose() method on the StreamReader when it exits, which in turn will call the Close() method). After that, I'd consider coming up with a way to keep the event from being fired when you set the selected index on the combobox (maybe use a flag or unwire/rewire the event handler).

It seems that you're changing the index of your combobox, thus writing to the same file before closing it. Call loca.Close() before writing to the file again.

comboBox1.SelectedIndex = index;
this will fire the event SelectedIndexChanged, so invoke the Close() method right behind ReadToEnd():
private void askforlocation()
{
if (File.Exists("location.txt"))
{
System.IO.StreamReader loc = new System.IO.StreamReader("location.txt");
string loca = loc.ReadToEnd();
loc.Close();//move that code to here
if (loca != "")
{
int index = comboBox1.FindString(loca);
comboBox1.SelectedIndex = index;
}
else
{
label6.Text = "Please select the location!";
}
//loc.Close();
}
else label6.Text = "Please select the location!";
}

Give this line loc.Close(); before setting the index of the combo box because the event is being raised earlier than you think.

You never need to call file.Close() or file.Dispose().
Please use a using statement ALWAYS (or mostly) when using a class that implements IDisposable. It will call the Dispose method for you.
using(System.IO.StreamReader loc = new System.IO.StreamReader("location.txt"))
{
string loca = loc.ReadToEnd();
}