At first, this exception doesn't really make sense to me. Why shouldn't i be able to duplicate this object multiple times? but thats not the point:
i use a List. Whenever i navigate to a site, it should do this:
(App.Current as App).recent.ForEach(x => container.Children.Add(x));
(container = another StackPanel)
the first time, it works. afterwards, i get the exception displayed in the questiontitle. i already tried using a listbox, but i just got a ArgumentException. I think these exceptions have the same source, but i don't know what i'm doing wrong. please help
thanks
The error is quite clear: A WPF/SL Control can only belong to 1 Parent control at a time.
So you'll either have to remove the Controls from their Parent when you are moving away from a Page or you'll have to Create (possibly Clone) new Controls in this ForEach.
When you navigate to a page, the old instance is not removed instantly, so when you add your controls to the new page, they may still be used in the old page if it's not destroyed, causing the exception.
Try overriding the OnNavigatedFrom(NavigationEventArgs e) and OnNavigatingFrom(NavigatingCancelEventArgs e) methods that are invoked when you leave a page so that you empty your StackPanel.
For example, you could do :
protected override void OnNavigatedFrom(NavigationEventArgs e)
{
base.OnNavigatedFrom(e);
container.Children.Clear();
}
You have to remove the container's children when you navigate from the page. But not if the navigation is due to a suspend. To avoid the children clear when the navigation is due to a suspend it is better to override OnNavigatingFrom instead of OnNavigatedFrom
protected override void OnNavigatingFrom(NavigatingCancelEventArgs e)
{
container.Children.Clear();
base.OnNavigatingFrom(e);
}
Related
I would like to run particular methods of a custom Camera class whenever the user zooms in or out in the helix toolkit view that my program is running inside of.
A key feature of this functionality is getting the mouseargs from the event so I can adjust the camera in a way that is proportional to the number of scroll ticks.
I began to try this:
public event PropertyChangedEventHandler PropertyChanged;
public virtual void onMouseWheeled(MouseDevice Mouse, int time,
MouseWheelEventArgs e) {
MouseWheel?.Invoke(this, new MouseWheelEventArgs(Mouse, time,
e.Delta)); }
//This next line goes in a MainWindow_Loaded method that gets called in the
//MainWindowConstructor
void MainWindow_Loaded(object sender, RoutedEventArgs e) {
view1.MouseWheel += new MouseWheelEventHandler(onMouseWheeled(Cursor,
Time.simTime, view1.MouseWheeledEventArgs)); }
but was having a lot of trouble figuring out how to pass a MouseWheelEventArgs object into the onMouseWheeled method when I'm trying to add the onMouseWheeled method to the MouseWheelEventHandler. Assuming nothing is fundamentally wrong with that sentence, which is nothing more than wishful thinking, The last thing I am trying to figure out is how to get mouse wheel event args so that I can pass it into a method.
Then I tried this:
public event MouseWheelEventHandler MouseWheel;
public virtual void onMouseWheeled(object sender, MouseWheelEventArgs e)
{
Console.WriteLine(e.Delta);
}
//In Main Window Loaded method...
void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
view1.MouseWheel += onMouseWheeled;
}
But I get no output when i scroll the wheel. I assumed this might actually work because view1 is the helix window I'm attaching all of my objects to, as children of view1.
Basically my main questions are:
What does invoke actually do? I only have this running to try to see if its working because onPropertyChanged methods I always use run the Invoke command like so. I'm actually not sure where I'm going with this.
How does the handler work?
How do the event args get called out so that I can use them and pass them as objects to other methods?
Thank you for your time. And Thank you twice for any and all pointers and advice you may give me.
Try to use preview mouse wheel event
I'm not sure but from my hours of debugging, this should be the best description of my problem I can give.
I'm creating a WinRT app, there are two pages- Main Page and Details Page. Inside Main Page constructor, I have initialized a listbox. On click of any of the element of listbox, user is taken to the Details page.
I'm just learning all this and design may not be best but here is what I did.
I took a static variable in MainPage.cs, and set it to point to the element which is clicked by the user. Now in the constructor of the Details page, I used this static variable to set the datacontext of Details Page itself.
What flow I'm expecting is:-
MainPage is created first. Listbox is setup.
User will click on any of the element of listbox. Itemclick event handler runs. It will set the static variable (of Mainpage.cs) to hold the infomation which item is clicked and navigate user to the Details page.
In Details page constructor, I have set the datacontext to point to some information based on the value of static variable mentioned in the previous step.
It works for most of the times, but once in like every 5 times, The Details page constructor throws an exception stating the static variable is not initialized yet. Why is Details page's constructor running when I'm starting the app? and why only sometimes? Do I need to set DataContext of Details Page in some other method instead of constructor?
The code is somewhat complex and too much in terms of domain of the problem so I'm avoiding posting it. But if I'm failing to explain the problem please tell, I'll post it keeping it as related as I can.
CODE:-
This is the method called when an item in listbox is clicked--will take user to the Details page.
private void overviewlistbox_Tapped_1(object sender, TappedRoutedEventArgs e)
{
MatchOverview selectedmatch = (sender as ListBox).SelectedItem as MatchOverview;
matchFullDetails = new ObservableCollection<Match>();
foreach (Match m in UpdateController.matchList)
{
if (m.matchDescription == selectedmatch.matchDesc)
{
matchFullDetails.Add(m);
break;
}
}
if(!(matchFullDetails.Count == 0))
this.Frame.Navigate(typeof(Details));
}
This is the constructor for Main Page:-
public static ObservableCollection<Match> matchFullDetails;
public MainPage()
{
matchFullDetails = new ObservableCollection<Match>();
this.InitializeComponent();
UpdateController update = new UpdateController(); // Creating new object will update the overview_list of UpdateController(static list).
overviewlistbox.ItemsSource = UpdateController.overview_list;
}
And this is the code for constructor of details page, where the exception occurs:-
public static ObservableCollection<Match> matchdetails = new ObservableCollection<Match>();
DispatcherTimer dtm_detailspage = null;
public Details()
{
this.InitializeComponent();
matchdetails = MainPage.matchFullDetails; // matchdetails.Last<>() is take because we only need item which is added latest to the collection.
if (matchdetails.Last<Match>().type == "TEST") // Exception is thrown here--Initialization
// error. When I check MainPage.matchFullDetails,
// no data is shown which means its not yet
// initialized. Also the exception is thrown either at
// the start of the app, or when details page is visited. That too once in 4-5 times, not always.
{
matchdetails.Add(matchdetails.First<Match>() as TestMatch);
}
if (matchdetails.Last<Match>().type == "ODI")
{
matchdetails.Add(matchdetails.Last<Match>() as ODIMatch);
}
if (matchdetails.Last<Match>().type == "T20")
{
matchdetails.Add(matchdetails.Last<Match>() as T20Match);
}
}
Exception Screenshot:-
Call Stack data on bug encounter:-
[Cricket Expert.exe!Cricket_Expert.Details.Details() Line 33 + 0x5 bytes
[External Code]
Cricket Expert.exe!Cricket_Expert.Common.SuspensionManager.RestoreFrameNavigationState(Windows.UI.Xaml.Controls.Frame frame) Line 236 + 0x5 bytes
Cricket Expert.exe!Cricket_Expert.Common.SuspensionManager.RestoreAsyn() Line 124 0x8 bytes
Cricket Expert.exe!Cricket_Expert.App.OnLaunched(Windows.ApplicationModel.Activation.LaunchActivatedEventArgs args) Line 74 + 0x5 bytes
[External Code]
MAJOR UPDATE:
I finally found the flaw. If the Details page is still active, and the app is restarted, the problem occurs.
Is there a solution to this problem??
You can pass information on what needs to be displayed on the Details page through the Navigate call and set the DataContext in OnNavigatedTo override to avoid using static variables. Pages don't get created unless you do it specifically e.g. by navigating to one. They might not be recreated if a page has NavigationCacheMode changed from the default (Disabled) so instances of the page can be reused during navigation calls. Ultimately it's hard to say what's wrong but it seems like something in your code and we couldn't help you if you don't share a sample that reproduces the problem.
*EDIT
One way to debug Details being created before MainPage would be to add this code at the beginning of the Details constructor:
if (MainPage.matchFullDetails == null)
{
System.Diagnostics.Debugger.Break();
}
Then look at the Call Stack panel in Visual Studio to see how it gets constructed.
One way to see if matchFullDetails is ever set to null is to search for its assignment (put a cursor on matchFullDetails in Visual Studio code editor and hit Shift+F12).
Another way would be to make matchFullDetails into a property and test it like this:
private static ObservableCollection<Match> _matchFullDetails;
public static ObservableCollection<Match> matchFullDetails
{
get
{
return _matchFullDetails;
}
set
{
if (value == null)
{
System.Diagnostics.Debugger.Break();
}
_matchFullDetails = value;
}
}
*EDIT 2
You can initialize your static property in a static constructor like this:
public static ObservableCollection<Match> matchFullDetails;
static MainPage()
{
matchFullDetails = new ObservableCollection<Match>();
}
public MainPage()
{
this.InitializeComponent();
UpdateController update = new UpdateController(); // Creating new object will update the overview_list of UpdateController(static list).
overviewlistbox.ItemsSource = UpdateController.overview_list;
}
this will prevent the null reference exception but won't fix your problem overall. When your app gets suspended and resumed - you have to restore the full state and it seems like your matchFullDetails collection would need to be serialized and saved to disk when your app gets suspended. Alternatively you might simply ignore the suspension manager call in App.xaml.cs and always start on home page, though that's not a very good experience and I am not sure if it satisfies app certification.
I have a strange problem with an AlphaAnimation. It is supposed to run repeatedly when an AsyncTask handler is called.
However, the first time the handler is called in the Activity, the animation won't start unless I touch the screen or if the UI is updated (by pressing the phone's menu button for example).
The strange part is that once the animation has run at least once, it will start without problem if the handler is called again.
Here's what the code looks like:
// AsyncTask handler
public void onNetworkEvent()
{
this.runOnUiThread(new Runnable() {
#Override
public void run()
{
flashScreen(Animation.INFINITE);
}
});
}
// Called method
private void flashScreen(int repeatCount)
{
final View flashView = this.findViewById(R.id.mainMenuFlashView);
AlphaAnimation alphaAnimation = new AlphaAnimation(1, 0);
alphaAnimation.setRepeatCount(repeatCount);
alphaAnimation.setRepeatMode(Animation.RESTART);
alphaAnimation.setDuration(300);
alphaAnimation.setInterpolator(new DecelerateInterpolator());
alphaAnimation.setAnimationListener(new Animation.AnimationListener() {
#Override
public void onAnimationStart(Animation animation)
{
flashView.setVisibility(View.VISIBLE);
}
#Override
public void onAnimationEnd(Animation animation)
{
flashView.setVisibility(View.GONE);
}
#Override
public void onAnimationRepeat(Animation animation) { }
});
flashView.startAnimation(alphaAnimation);
}
I have noticed that runOnUIThread isn't necessary (same results occur if I don't use it), but I prefer keeping it as I'm not on the UI thread.
Any ideas on what could cause this?
A little more research showed that my problem was the same a this question:
Layout animation not working on first run
The flashView's visibility was set to GONE by default (causing the Animation not to start immediately as the View had never been rendered), so I just need to set it to INVISIBLE before calling flashView.startAnimation()
If setting the View to VISIBLE won't work, as was in my case, it helped for me to call requestLayout() before starting the Animation, like so:
Animation an = new Animation() {
...
view.requestLayout();
view.startAnimation(an);
In my case, my View was 0dip high which prevented onAnimationStart from being called, this helped me around that problem.
This worked for me:
view.setVisibility(View.VISIBLE);
view.startAnimation(animation);
I had to set the view to VISIBLE (not INVISIBLE, neither GONE), causing the view renderization needed to animate it.
That's not an easy one. Till you got a real answer : The animation start is triggered by onNetworkEvent. As we don't know the rest of the code, you should look there, try to change onNetworkEvent by an other event that you can easily identify, just to debug if the rest of the code is ok or if it's just the trigger that is responsible for it.
May be it will help someone, because previous answers not helped me.
My animation was changing height of view (from 0 to it's real height and back) on click - expand and collapse animations.
Nothing worked until i added listener and set visibility to GONE, when animation ends:
collapseAnim.setAnimationListener(new Animation.AnimationListener() {
#Override
public void onAnimationStart(Animation animation) {
}
#Override
public void onAnimationEnd(Animation animation) {
view.setVisibility(View.GONE);
}
#Override
public void onAnimationRepeat(Animation animation) {
}
});
And when expand just set it to VISIBLE before animation:
view.setVisibility(View.VISIBLE);
view.startAnimation(expandAnim);
The objects passed as arguments are only received an Navigation event. I want to receive them on Click Event,what should I use instead of Parameter??
void App1::MainPage::btuN_Click(Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e)
{
Variables^ data = (Variables^)e->OriginalSource;
if (data->sNotf!=nullptr)
Frame->Navigate(TypeName(BlankPage3::typeid), data);
}
I used OriginalSource, but it didn't work. Would any one help me? Thanks in Adv
OriginalSource property contains a reference to the object that raised the event. It has nothing to do with navigation parameters.
I'm not exactly sure which parameters you'd like to access in your button click event. The ones passed to your page in its navigation event? In this case you should handle said navigation event, retrieve the parameters there and store them into a private field of your page. In click event you can then read them back from the private field and pass them forward.
On a related note: passing non-basic types as navigation parameters is discouraged. If you need to do that, it's a better idea to just pass the object ids and read their values inside the page from a common repository.
When you navigate to your page, if the parameters from your navigation event are important, you should store them within your page object so it can be accessed later.
//MainPage needs to have a private Variables^ named Info
void MainPage::OnNavigatedTo(NavigationEventArgs^ e)
{
if(e->Parameter)
this->Info = dynamic_cast<Variables^>(e->Parameter);
}
And then access that variable from within your click handler:
void MainPage::btuN_Click(Platform::Object^ sender, Windows::UI::Xaml::RoutedEventArgs^ e)
{
if(this->Info)
if (this->Info->sNotf!=nullptr)
Frame->Navigate(TypeName(BlankPage3::typeid), Info);
}
I've got a contributed command and a handler for it. The handler's execute event has to get the value for the property actually selected in the properties view and act on it, or to be disabled if no property selected.
I've tried:
1) Set the selection provider to something which provides selection from the property view. Something in this case is just PropertySheetViewer for my PropertySheetPage, but i can't set it as the selection provider because the PropertySheetPage's viewer is private and has no getter.
2) Overriding PropertySheetPage's createControl method: This method creates a Tree control for the PropertySheetViewer. A selection listener can be installed for that tree control, so maybe i can make my command handler implement SelectionListener... The solution would be somethin like:
In my editor:
public Object getAdapter(#SuppressWarnings("rawtypes") Class type) {
if (type == IPropertySheetPage.class) {
PropertySheetPage page = new PropertySheetPage() {
#Override
public void createControl(Composite parent) {
super.createControl(parent);
IHandler handler = someWayToGetMyCmdHandler();
((org.eclipse.swt.widgets.Tree) getControl())
.addSelectionListener(handler);
}
};
IPropertySheetEntry entry = new UndoablePropertySheetEntry(
getCommandStack());
page.setRootEntry(entry);
return page;
}
return super.getAdapter(type);
}
And my command handler implementing SelectionListener as i said... The problem with this approach is that i can't find a way to get a reference to my contributed command handler (someWayToGetMyCmdHandler() above).
Has anybody got any clue on this, or any other possible approach to the problem??
There's handleEntrySelection(ISelection selection) method in PropertySheetPage that you could override to be notified about selection changes in the viewer (although PropertySheetPage is #noextend).
The second part (updating the handler) is a bit more tricky than it would normally be. Commands/handlers get updated automatically when workbench selection changes (you just need to implement setEnabled(Object evaluationContext) AbstractHandler). But since PropertySheetPage is designed to change its input on global selection change, then you have to find some custom way to notify/update your handler.
As I understand, it is currently not possible to extend the platform command event handling mechanism with custom variables, so you just need to directly look up your handler using IHandlerService of the workbench.