I followed this link http://www.wintellect.com/devcenter/jprosise/handling-the-back-button-in-windows-10-uwp-apps and "successfully" make my button work. I mean I can make my backbutton work between pages. However, if I navigate to a control which is inside this page and will cover the whole screen, then it would not allow me to back to the page. I will stuck in that control.
I'm wondering how to solve this problem. Currently I can think two possible ways (0) Override OnBackRequested() inside the control's code behind or viewmodel? (1) Override OnHardwareButtonsBackPressed() inside the control's code behind or viewmodel?. I don't know if these are correct way to do it or there is some better way to do it. Another reason for me to override is that I need to make some changes to the page navigation behavior.
As you have guessed, you simply need to hide the control again when the back button is pressed or back is requested in some other way. I would listen for the BackRequested event (not the HardwareButtons.BackPressed event) in the page's code-behind, and in the handling method you can check to see if the control is currently shown. The reason I recommend the BackRequested event is because it is universal, while HardwareButtons.BackPressed only works on a phone. Anyway, if the control is visible, then hide it, and set the Handled property of the event arguments to true. If the control is already hidden, don't do anything special to handle the event (because in that case you will want the navigation system to handle it by navigating to the previous page, if there is one). There are many aspects to navigation in Windows 10 -- please see these pages on Navigation and the SystemNavigationManager.
Related
I'm working in a legacy application using MFC.
We have a mechanism to enable/disable controls depending on some business logic.
This mechanism is implemented in the CView-derived class. The way it works is all the views in the application derived from a common CView-derived class (CBaseView) and on the PreTranslateMessage all controls of the view are enabled/disabled.
This worked fine so far because all controls send at least WM_PAINT message when they need to be painted. So the system worked without the user having to move the mouse or anything. I recently added some drawing features and I had to use WS_EX_COMPOSITE to get ride of some flickering. With this flag activated my CView-derived class is not getting any called to PreTranslateMessage when creating the view....so the controls are not disabled until the user moves the mouse over the control.
I understand there is no way to send WM_PAINT using WS_EX_COMPOSITE but is there other message I can use to get the same behaviour???
Edited:
I am currently using the OnIdle approach but it has a big drawback, the windows doesn't become idle until after drawing all the controls...so when you enter the screen al controls are enabled and inmediately they are disabled...this makes a quite ugly effect!
More solutions???
Thanks in advance...
The logical place to enable/disable controls would be CView::OnUpdate, it is called by the framework after the view's document has been modified and from OnInitialUpdate(); you can also call this function if there is some change that would trigger re-evaluation of your business logic.
EDIT
After reading the question a bit more closely, what you could also do is to post a private message at the end of OnInitialUpdate and "catch" it in your PreTranslateMessage:
PostMessage(WM_APP, 0, 0);
Calling InvalidateRect followed by UpdateWindow against the window in question will mark the entire client area as dirty and force an immediate repaint. Remember that WM_PAINT is not really a message, in the queue in the usual sense, it is pushed out after all other messages have been processed for that window, which would include any invalidations of the area being drawn. No message is generated at all if there are no invalid segments of the active window display.
Is there a way to get a callback when a View appears/disappears on the screen?
I need this for analytics purposes - eg. I need to check how many times people saw a view versus how many times they clicked on it.
I can tell whether a view is on screen at a certain point in time but I'm wondering whether there is a callback for that.
Also note that I'm not interested when a View's state becomes VISIBLE and not even when a view gets rendered (because eg. in a ViewPager the Views of the second page are rendered before they actually appear on screen).
We did several workarounds for certain scenarios but I'd like to have something which is more generic. We need it in ListViews, GridViews, ScrollViews and ViewPagers and each one of them presents different challenges.
Does ViewTreeObserver.OnGlobalLayoutListener help? I have never used it myself though.
See: http://developer.android.com/reference/android/view/ViewTreeObserver.OnGlobalLayoutListener.html
Does MvvmCross support a cross platform solution for displaying alerts or popups?
Searching the code I found MvxDialogActivityView but it has been commented out. Will this remain the case for now?
If there is no direct support how would you suggest this is best done? (Perhaps the ViewModel would change a property and call FirePropertyChanged so that the View would be aware of it and show an alert.)
Edit 16:04 16th June 2012
What I am trying to do for this specific case is as follows:
On the page a button is clicked, which causes a method to run in the ViewModel which does an evaluation to determine which of two messages should be shown to the customer. The message would be shown as an alert or popup (either native, or preferably totally styled by me). The message would fade after (the click of the OK button, or preferably 3 seconds).
After the message has been dismissed a new page will be navigated too (depending on which of the two messages was shown).
How to handle this definitely depends on what the situation is - there's no single best rule (IMHO)
For a general error display pattern, there's one proposal at http://slodge.blogspot.co.uk/2012/05/one-pattern-for-error-handling-in.html
I've used similar patterns for showing application level notifications - e.g. for when a long running operation completes or when a chat message arrives or...
One interesting post about how to display message boxes was: http://awkwardcoder.blogspot.co.uk/2012/03/showing-message-box-from-viewmodel-in.html - I'm not sure I'd completely follow the end solution, but there are definitely some good points there about what not to do.
For your updated scenario, I would consider using a messenger (like TinyMessenger) or using normal C# events exposed by the ViewModel and consumed by its View
On the page a button is clicked, which causes a method to run in the ViewModel
I would implement this using an ICommand bound to the button Click/Tap/TouchDown
which does an evaluation to determine which of two messages should be shown to the customer.
I would definitely implement the logic within a Service
This would be called from the ViewModel - and the result/decision would probably cause some property or private field state change.
How does the View then decide to show a message? I can think of 3 options:
The View could just respond to a Property change (normal Mvvm INPC) - this would be my preference
The ViewModel could expose a normal C# event which it triggers...
The ViewModel could send a Message
This last option (Messenging) is probably the most flexible solution here - it decouples the View and ViewModel in case you later decide to change responsibilities. To implement messenging, either:
implement your own hub (like I do for errors in http://slodge.blogspot.co.uk/2012/05/one-pattern-for-error-handling-in.html)
or use a generic solution like TinyMessenger
The message would be shown as an alert or popup (either native, or preferably totally styled by me).
This is a View concern - so would be entirely controlled by the View project. I'd use controls like: UIAlert, Toast, ToastPrompt, etc - all of which can be styled
The message would fade after (the click of the OK button, or preferably 3 seconds). After the message has been dismissed...
I'd use some form of Code Behind (or maybe a Behaviour in WP7) in the View. This would detect the click/fade/disappear and would then invoke either an ICommand (my preference) or public method on the ViewModel
a new page will be navigated too
This navigation would be requested from the ViewModel
(depending on which of the two messages was shown).
This would be easy to track through the above flow... presumably the ViewModel already knows what to show.
So that's what I'd do...
it keeps the application flow logic inside the ViewModels (and lower)
it keeps the presentation inside the Views
...but I'm sure there are other options :)
One final note... the fade out and then navigate logic can really get "messed up" by Switching/Tombstoning on WP7 and Android - this may or may not matter for your particular scenario.
Actually, I want to store some data in background page and the popup page just show that part of data say Data as a div element created in background page document.createElement("div"). Here, the background page will register some listeners to the tab update and change the Data elements accordingly. What the popup will do is to get that Data and appendit use the document.appendChild(Data).
(The purpose I intend is this will cause the popup changes immediately while the tab updage is triggered.)
However, the elements are shown as usual, what I am facing very headache is I have registered the onclick for the div object in backgroundpage as onclick="chrome.extension.getBackgroundPage().somefunc()". However, the first time, all the click will triger the right behavior but after the popup loses foucs and get focus again, all the click won't work.
I try to put something like change the onclick="somefunc()" and leave the func within the script of popup page. And there I want to log whether it is called by console.log("clicked"). Here, something unbelievable happens, the function is succefully trigerred BUT the console is null here, I cannot even call chrome.extension.getBackgroundPage() as well.
Here are a list of questions, maybe very hard to express for me...
1. Whether I can reuse the DOM element from the background page to the popup page directly by appendChild(chrome.extension.getBackgroundPage().getElementById()?
2.Will the onclick event registered in the background page still work in the popup pages?
3. What's the problem with the problem I am encountering? I have tried many ways to find out the reason but all in vain at last...
Best Regards,
If you need any more information, please let me know.
(PS: I am wonderning if it is called something like the event propogation, however, I am not an expert in this two pages communicating...)
I want to able to create reusable user controls within my web app and i'm wondering on how to go about doing so.
Should a user controls properties be
visible to a form that's using it?
What's the best way to go about
loading the controls on the user
control from the form thats using
it? Should there be a public method
within the control that allows you
to load it from an external form or should the user
control be loaded in the page load
event
Is it okay to nest user controls within user controls?
etc...
Thanks for any advice
1) You only need to make properties visible if any page needs to read or modify information on your control. I personally like to keep my user controls as self contained as possible, and keep this to a minimum.
2) I would just rely on the built in page life cycle to render your control, but it is important to note when each of your control's events fire in relation to your pages. You may find that there are times that you need something on your control to render before something on your page does. In this case you will need to rely on the page_init in your control more than the page_load of your control.
3) You technically can nest user controls, but things will get tricky if you need to start reading and writing information (as in your first question) from any of the nested controls. Also, the page life cycle of the nested controls gets even more important. I would avoid this if you can.