There are a lot of samples showing how to pass a parameter on navigating to a page in Window 8 (WinRT). But I could not find any hint for passing parameters going back.
Situation: The user navigates to a details page of same data. The data is passed to the page by
Frame.Navigate(typeof(DedtailsPage), data);
How can I pass back the changed data on GoBack()?
Store the reference to data somewhere and retrieve it when you navigate back?
Also note that it's best not to pass objects other than simple strings or values between pages, since only simple types are supported for storing frame navigation state in case your app gets suspended.
I know, that this is a very bad idea, but usualy I use this:
To write:
Frame rootFrame = Window.Current.Content as Frame;
rootFrame.Tag = myObject1;
To read:
Frame rootFrame = Window.Current.Content as Frame;
var myObject2 = rootFrame.Tag;
I've made another choice to handle this.
Keep in mind that I'm a Xamarin developer (not Forms!) so i was looking for a solution which was similar for all platforms: iOS, Android and Windows.
I am a great fun of events, rather than passing objects or storing globals.
So the best choice to pass data from PageB (the child) to PageA (the parent) is to communicate via events.
Some notes: In iOS and Android, when you navigate from a "page" to "page" you can do this by passing an instance of the target object you want to navigate to. In iOS you create an instance of a custom UIViewController. In Android you create an instance of a custom Fragment. Doing this allow you to attach events handler to your instances.
An example:
var controller = new ExtrasViewController();
controller.ExtraSelected += ExtrasFragment_ExtraSelected;
controller.ExtrasCleared += ExtrasFragment_ExtrasCleared;
this.NavigationController.PushViewController(controller, false);
In WinRT Apps you are only allowed to pass "types" of target page to navigate to. So the only way to attach event handlers to your page instance is to use the OnNavigatedFrom method from the calling page. So suppose you are in PageA and want to attach some event handlers to your PageB, before it become active, simply write in your PageA "code behind":
protected override void OnNavigatedFrom(NavigationEventArgs e)
{
base.OnNavigatedFrom(e);
var page = e.Content as ExtraBody;
if(page != null)
{
page.ExtraSelected += ExtrasFragment_ExtraSelected;
page.ExtrasCleared += ExtrasFragment_ExtrasCleared;
}
}
Related
I have a Windows 10 Universal Windows Platform app with multiple pages, a main page, a list page and a details page and use the following to navigate to List page:
this.Frame.Navigate(typeof(ListPage), parameter);
When you are on the list page you can select an item which will launch a details page like so:
this.Frame.Navigate(typeof(DetailsPage), parameter);
Which works fine, the parameter is a selected Id or information then when using the Back button which on a Desktop app or Phone uses:
this.Frame.GoBack();
This always returns to the MainPage, that is when go from Main, to List to Details hitting back goes to Main, how do I get the GoBack to Go back to the previous page, it always seems to go home rather than the user expected behaviour, an ideas how to resolve this?
I’ve seen this before when you subscribe to the HardwareButtons.BackPressed event (or whatever the equivalent is in a Win10 UWP app) on a page, but then don’t unsubscribe from it. This means two event handlers get called when pressing Back, and both event handlers call Frame.GoBack().
I always subscribe to the event in the page’s NavigatedTo event, and unsubscribe in the NavigatedFrom event.
Could this be happening with your app?
If every page in your app should have the same behaviour, i.e. go back to the previous page, then subscribe to the back button event in the app class as suggested by #RoguePlanetoid in the comments:
SystemNavigationManager.GetForCurrentView().BackRequested += OnBackRequested;
The OnLaunched method would be a good place to do this. Don't forget to tell the OS to display the back button when the app is running on a desktop or tablet:
SystemNavigationManager.GetForCurrentView().AppViewBackButtonVisibility = AppViewBackButtonVisibility.Visible;
Then, add an event handler in the app class like this:
private void OnBackRequested(object sender, BackRequestedEventArgs e)
{
Frame rootFrame = Window.Current.Content as Frame;
if (rootFrame.CanGoBack)
{
e.Handled = true;
rootFrame.GoBack();
}
}
If you want different behaviour on different pages when back is pressed, i.e. ask the user to confirm losing their changes or something, then subscribe to the back button event in a pages OnNavigatedTo method (the code will be same as above), but make sure you unsubscribe in the page's OnNavigatedFrom event:
protected override void OnNavigatedFrom(NavigationEventArgs e)
{
SystemNavigationManager.GetForCurrentView().BackRequested -= this.OnBackPressed;
base.OnNavigatedFrom(e);
}
How can I implement removing the backStack Entry in Metro style applications?
frame.SetNavigationState("1,0");
will clear the navigation history for you.
I found this answer useful:
How to clear Backstack of the frame and start afresh
Write your own NavigationService and store the navigationstate in the constructor.
string state;
public NavigationService(Frame mainFrame)
{
state = mainFrame.GetNavigationState();
_mainFrame = mainFrame;
_mainFrame.Navigating += _mainFrame_Navigating;
}
Then implement this method on the service and call it when needed:
public void ClearBackstack()
{
_mainFrame.SetNavigationState(state);
}
It doesn't seem to be possible. If you want to clear the back stack entirely (e.g. if you have a "home" button), you can use the code supplied in the LayoutAwarePage.cs file in the grid sample app.
if (this.Frame != null)
{
while (this.Frame.CanGoBack) this.Frame.GoBack();
}
While this doesn't actually clear the stack, it does take you back to the program's start location and there will be no further back-direction entries in the list. If you want to back out of a dead-end page by pressing a button, you could modify this behaviour to step back a number of pages and effectively remove the back entries.
Let's say in a view I have a DojoX Mobile ListItem that is pulling an HTML view fragment into the DOM via AJAX and then transitioning to that view. Assume this is all working fine.
Now, I go back to the initial view that had that ListItem on it and click some other button that destroys that view node from the DOM. If I now click on that ListItem that previously loaded that view node into the DOM (which has now been removed), it will try to transition to a view that doesn't exist. It doesn't know that it has been removed.
Is there some type of way to tell a ListItem that it needs to fetch the HTML again because what was previously fetched no longer exists? I am not seeing anything about doing this in any documentation anywhere. I don't think a code sample is really necessary here, but I can provide a minimal one if necessary.
I went a different route and left the view exist in the DOM, and simply made a function that clears all sensitive data out of the view.
Okay, in this case, i guess you could hook the onShow function of your ListItem container(or any other onchange event). Create a listener for said handle to evaluate if your item needs reloading. Following is under the assumtion that it is the item.onclick contents showing - and not the label of your item which contains these informations
Or better yet, do all this during initialization so that your ListItem container will be an extended with custom onClick code.
Seems simple but may introduce some quirks, where/when/if you programatically change to this item, however here goes:
function checkItem() {
// figure out if DOM is present and if it should be
if( isLoggedIn() ) {
this.getChildren().forEach(function(listitem) {
if( dojo.query("#ID_TO_LOOK_FOR", listitem.domNode).length == 0 ) {
// this references the listItem, refresh contents.
// Note: this expects the listitem to be stateful, have no testing environment at time being but it should be
listitem.set("url", listitem.url);
}
});
}
}
Preferably, set this in your construct of the container for your ListItems
var listItemParent = new dojox.mobile.RoundRectList({
onShow : checkItem,
...
});
Or create listener
var listItemParent = dijit.byId('itemRegistryId');
// override onClick - calling inheritance chain once done
dojo.connect(listItemParent, "onClick", listItemParent, checkItem);
Here is what I'd like to do :
I have an Silverlight application using navigation frame and MEF. (like this one : http://msdn.microsoft.com/en-us/magazine/gg535672.aspx)
This application consists of a set of buttons. Each button click load a view and its associated ViewModel.
Within theses views, I've a list with items and when I click on each items it refreshs a kind of sub-view in this view.
I'd like to create a navigation system : for example myapp.aspx#view1/2, where 2 is in fact the item clicked in the list. If I click on one of the button, it would load a default item and refresh all the view, but when I click on an item, I wouldn't like to refresh all the view but only certain part of the view (I do not want to create another instance of the view and viewmodel).
My problem is in fact that I would like to get the best pratice to get a reference to an existing view or viewmodel when i'm navigating to this page that has already been loaded (for example from myapp.aspx#view1/2 to myapp.aspx#view1/3)(I plan to do this into the BeginLoad of the ContentLoader class)
If I get the viewmodel, I can do that I want by changing for example the current itemId property which could refresh the view thanks to binding.
Thanks in davance if you have something to propose.
A common approach is to use some form of Messenger to do this type of operation. The item's click could trigger the sending of a message, with the Item attached. The ViewModel in question would be a subscriber, and edit its current settings (ie: it's ItemId, which would trigger the binding refresh).
The most common implementations are usually ones similar to the Messenger service in MVVM Light.
It's fairly easy to roll your own here, though, especially since you're already using MEF. Just create a service to handle the message passing, and import it into both endpoints.
Actually, I would have prefered to use an URI to navigate in my application when I click on an item, but if I use an URI, the entire view is reloading and not the specific part I'd like to.
With the messenger, I won't be able to use navigation with url within the view, I think ? Or else I didn't really figure out what you proposed to me.
The algorithm I would like to take is :
navigate("...asp#MyView1/1")
MyView1 is current view ?
yes then I'd like to get the viewmodel of the current view and change it the ItemId property with 1
no, then the view will be created
And I'd like to implement this algorithm there : (this is the place where the view is instancied for each navigation, in my CompositionNavigationContentLoader class)
public IAsyncResult BeginLoad(Uri targetUri, Uri currentUri, AsyncCallback userCallback, object asyncState)
{
// Convert to a dummy relative Uri so we can access the host.
var relativeUri = new Uri("http://" + targetUri.OriginalString, UriKind.Absolute);
// Get the factory for the ViewModel.
var viewModelMapping = ViewModelExports.FirstOrDefault(o => o.Metadata.Key.Equals(relativeUri.Host, StringComparison.OrdinalIgnoreCase));
if (viewModelMapping == null)
throw new InvalidOperationException(
String.Format("Unable to navigate to: {0}. Could not locate the ViewModel.", targetUri.OriginalString));
// Get the factory for the View.
var viewMapping = ViewExports.FirstOrDefault(o => o.Metadata.ViewModelContract == viewModelMapping.Metadata.ViewModelContract);
if (viewMapping == null)
throw new InvalidOperationException(
String.Format("Unable to navigate to: {0}. Could not locate the View.", targetUri.OriginalString));
// Resolve both the View and the ViewModel.
var viewFactory = viewMapping.CreateExport();
var view = viewFactory.Value as Control;
var viewModelFactory = viewModelMapping.CreateExport();
var viewModel = viewModelFactory.Value as IViewModel;
// Attach ViewModel to View.
view.DataContext = viewModel;
viewModel.OnLoaded();
Thanks.
I'm trying to speed up my windows phone 7 page load times. I have a 'static' page that has a dynamically created in a Panorama control - static meaning that the content never changes.
On the first load I look at my config file, create the individual PanoramaItem controls and add them to the main Panorama control. I'm trying to keep a List in a static place so that the initial creation would only happen once and I could just add a fully rendered version to my Panorama control when the page was rendered.
Works fine on first load, but when I try to add the cached PanoramaItems to the Panorama control I get the message "Element is already the child of another element". This makes sense since I already added before. But I can see a way to disconnect the PanoramaItems with the first Panorama control...
I could be going about the control caching thing all wrong as well... Let me know if there's another way to do this.
You can use Panorama.Items.Remove(pivotItem) for this
As an example
With the following page fields
PanoramaItem pi;
bool blahShown = false;
On the press of this button, the control is first instantiated and displayed and on subsequent presses removed and readded without instantiation.
private void button1_Click(object sender, RoutedEventArgs e)
{
if (pi == null) {
pi = new PanoramaItem();
pi.Header = "blah";
}
if (blahShown) {
Pano.Items.Remove(pi);
blahShown = false;
} else {
Pano.Items.Add(pi);
blahShown = true;
}
}