I have made a HomeViewModel which contains some other ViewModels to be presented in a TabParPresenter. This works fine and the ViewModels associated Views are presented correctly in their corresponding tabs. However on of the ViewModels have a check in the ctor that tells it in when some conditions apply it needs to navigate to SettingsViewModel , which is not a part of the ViewModels contained in HomeViewModel.
The navigation event gets caught by the TabBarPresenterHost, which is simply the Presenter of the application and if a TabBarPresenter is present and not null it is passed to the TabBarPresenter.ShowView() method. All this happens before the TabBarPresenter is done loading and SelectedViewController is set in ViewDidLoad. Hence the TabBarPresenter relies on using the SelectedViewController to push new Views I obviously get a Null Reference Exception.
In short what I want is:
if (conditionForShowingHome == true)
GoToHome();
else
GoToSettings();
Then when inside SettingsViewModel I have set the stuff I need when going back you return to HomeViewModel.
What breaks this is that the ViewModels are loaded before the View is done loading and the navigation event is executed before the View is done loading. Any ideas how to go around this?
I'm afraid that putting this code inside a ViewModel constructor is likely to lead to problems.
The ViewModel constructors are called during navigations - and not all platforms will support starting new navigations while existing ones are still in progress.
To workaround this, I personally opt to put this type of behaviour in the code before the navigation.
In the case of a normal navigation, this can go inside an MvxCommand execution handler.
In the case of application startup, I do this in a custom app start - see some notes in https://speakerdeck.com/cirrious/appstart-in-mvvmcross
Related
I found this question, but it does not appear to be resolved, and I also have more to add.
First off, the linked question defines pretty much the same issue that I am having.
1. I am using the application layout control from the ExtLib
2. It does not matter if the button is in that control or not.
3. CSJS actions will fire from the button, SSJS actions will not fire.
4. No errors are present
5. Browser / cache is irrelevant as the server side action just will not fire.
After seeing the linked question, I looked in the Local file in the package view and found an anomaly that makes me wonder if it could be the cause. I have never seen such a file before and even looked in my other xpage projects just to be sure.
This file cannot be deleted, and when clicked upon, the display window says that the element does not exist.
Does anyone know what this file is, how I can remove it, or could it be that my application is corrupted?
**More Info **
The following snippet is copied from the java file for the XPage located in the Local directory. Everything looks fine to me.
private UIComponent createEventHandler(FacesContext context,
UIComponent parent, PageExpressionEvaluator evaluator) {
XspEventHandler result = new XspEventHandler();
String sourceId = "button2/xp:eventHandler[1]/xp:this.action[1]/text()";
MethodBinding action = evaluator.createMethodBinding(result,
"#{javascript:view.postScript(\"alert(\'server script fired!\')\");}",
null,null, sourceId);
result.setAction(action);
result.setSubmit(true);
result.setEvent("onclick");
result.setRefreshMode("complete");
return result;
}
EDIT
Moving all of the design elements into a new .nsf so that file is no longer present does not change the problem of the SSJS onclick action not firing. That strange file is however not present.
Is it failing on a converter / validator? That can cause it to skip out of the lifecycle before Invoke Application phase. To test whether a button is actually working, you can also use "Do not validate or update data". Then the SSJS runs in Apply Request Values phase. If the SSJS is triggered (you won't have the latest data from the browser in the data model or components though), then it's another good bet for converter or validator failure.
I have a nested control (NC1) which contains 3 instances of NC2. When the containing view is first opened, NC1 will be null and so the three instances of NC2 will be null. This appears to work correctly based on debugging through my code and the framework.
When a selection is made in the containing view NC1 is properly set (and the ViewModel is (re)created) and values for its properties (exposed through Fody.Expose) appear in the view. However, none of the ViewModels for NC2 are (re)created and they do not reflect the values provided by their respective models.
I am not sure exactly what information to provide without uploading a lot of content, so I will take a stab.
In the NC1 view, I have the following
<localViews:NC2 DataContext="NC2Entry1"/>
<localViews:NC2 DataContext="NC2Entry2"/>
<localViews:NC2 DataContext="NC2Entry3"/>
NC2EntryX are properties on the NC1 ViewModel that return a specific instance of an NC2 model from a list. The NC2EntryX properties is NOT registered with RegisterProperty.
As a note, I have discovered that I must have an empty parameter constructor for the NC1 and NC2 view models. If I do not, then I receive a MissingMethod exception when the view model is being created when the TypeFactory attempts to create the ViewModel with the Activator instead of using the injection path. The injection path is not used because the call at line 591 of TypeFactory returns false because the NC2 model passed is 'not registered'. (Not sure if it should be or how to make it so.)
I am using Catel version 3.9.0
The NC2EntryX property changes must be reflected to the view somehow. You can do this by making it Catel properties, or by calling RaisePropertyChanged("NC2EntryX") yourself when setting the property value. Only in that case the view will be updated (this is just standard WPF / MVVM behavior).
About the missing method exception: it is a first chance exception where the TypeFactory tries to fall back to Activator.CreateInstance when it fails to create the type with dependency injection. No need to worry about this. If you don't want view models to be alive without a model, don't create an empty constructor.
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.
I hope someone can help me solve a very serious problem we face at the moment with a business critical application losing data when a user works in it.
This happens randomly - I have never reproduced this but the users are in the system a lot more than me.
A document is created with a load of fields on it, and there are 2 rich text fields. We're using Domino 8.5.3 - there are no extension lib controls in use. The document has workflow built in, and all validation is done by a SSJS function called from the data query save event. There is an insane amount of logging to the sessionscope.log and also this is (now) captured for each user in a notes document so I can review what they are doing.
Sometimes, a user gets to a workflow step where they have to fill in a Rich Text field and make a choice in a dropdown field, then they submit the document with a workflow button. When the workflow button is pressed (does a Full Update) some client side JS runs first
// Process any autogenerated submit listeners
if( XSP._processListeners ){ // Not sure if this is valid in all versions of XPages
XSP._processListeners( XSP.querySubmitListeners, document.forms[0].id );
}
(I added this to try and prevent the RTF fields losing their values after reading a blog but so far it's not working)
then the Server-side event runs and calls view.save() to trigger QS code (for validation) and PS code to run the workflow agent on the server.
95% of the time, this works fine.
5% of the time however, the page refreshes all the changes made, both to the RFT field (CKEditor) and the dropdown field are reloaded as they were previously, with no content. It's like the save hasn't happened, and the Full Update button has decided to work like a page refresh instead of a submit.
Under normal circumstances, the log shows that when a workflow button is pressed, the QuerySave code starts and returns True. Then the ID of the workflow button pressed is logged (so I can see which ones are being used when I am reviewing problems), then the PostSave code starts and finally returns true.
When there is a problem, The QuerySave event runs, returns true if the validation has passed, or false if it's failed, and then it stops. The ID of the workflow button is also logged. But the code should continue by calling the PostSave function if the QuerySave returns true - it doesn't even log that it's starting the PostSave function.
And to make matters worse, after the failure to call the PostSave code, the next thing that is logged is the beforePageLoad event running and this apparently reloads the page, which hasn't got the recent edits on it, and so the users loses all the information they have typed!
This has to be the most annoying problem I've ever encountered with XPages as I can find no reason why a successful QuerySave (or even a failure because mandatory fields weren't filled in) would cause the page to refresh like this and lose the content. Please please can someone help point me in the right direction??
It sounds as if in the 5% use cases, the document open for > 30mins and the XSP session is timing out - the submit causes the component tree to be re-created, and the now empty page returned back to the user. Try increasing the time out for the application to see if the issue goes away.
I would design the flow slightly different. In JSF/XPages validation belongs into validators, not into a QuerySave event. Also I'd rather use a submit for the buttons, so you don't need to trigger a view.save() in code. This does not interfere with JSF's sequence of things - but that's style not necessarily source of your problem.... idea about that:
As Jeremy I would as a first stop suspect a timeout, then the next stop is a fatal issue in your QuerySave event, that derails the runtime (for whatever reason). You can try something like this:
var qsResult = false;
// your code goes here, no return statements
// please and if you are happy
qsResult = true;
return qsResult;
The pessimistic approach would eventually tell you if something is wrong. Also: if there is an abort and your querySave just returns, then you might run in this trap
function noReturn() {return; } //nothing comes back!
noReturn() == true; --> false
noReturn() == false; --> false
noReturn() != false; --> true!!!!
What you need to check: what is your performance setting: serialize to disk, keep in memory or keep latest in memory? It could be you running foul of the way JavaScript libraries work.
A SSJS library is loaded whenever it is needed. Variables inside are initialized. A library is unloaded when memory conditions require it and all related variables are discarded. so if you rely on any variable in a JS Function that sits inside a SSJS library between calls you might or might not get the value back, which could describe your error condition. Stuff you want to keep should go into a scope (viewScope seems right here).
To make it a little more trickier:
When you use closures and first class functions these functions have access to the variables from the parent function, unless the library had been unloaded. Also functions (you could park them in a scope too) don't serialize (open flaw) so you need to be careful when putting them into a scope.
If your stuff is really complex you might be better off with a backing bean.
Did that help?
To create a managed bean (or more) check Per's article. Your validator would sit in a application bean:
<faces-config>
<managed-bean>
<managed-bean-name>workflowvalidator</managed-bean-name>
<managed-bean-class>com.company.WfValidator</managed-bean-class>
<managed-bean-scope>application</managed-bean-scope>
</managed-bean>
</faces-config>
Inside you would use a map for the error messages
public Map<String,String> getErrorMessages() {
if (this.errorStrings == null) { // errorStrings implements the MAP interface
this.loadErrorDefinitions(); //Private method, loads from Domino
}
return this.errorStrings;
}
then you can use EL in the Error message string of your validators:
workflowvalidator.errorMessage("some-id");
this allows XPages to pick the right one directly in EL, which is faster than SSJS. You could then go and implement your own custom Java validator that talks to that bean (this would allow you bypass SSJS here). Other than the example I wouldn't put the notes code in it, but talk to your WfValidator class. To do that you need to get a handle to it in Java:
private WfValidator getValidatorBean() {
FacesContext fc = FacesContext.getCurrentInstance();
return (WfValidator) fc.getApplication()
.getVariableResolver()
.resolveVariable(fc, "workflowvalidator");
}
Using the resolver you get access to the loaded bean. Hope that helps!
My experience is that this problem is due to keeping page in memory. Sometimes for some reason the page gets wiped out of memory. I'm seeing this when there is a lot of partial refreshes with rather complex backend Java processing. This processing somehow seems to take the space from memory that is used by the XPage.
The problem might have been fixed in later releases but I'm seeing it at least in 8.5.2.
In your case I would figure out some other workaround for the CKEditor bug and use "Keep pages on disk" option. Or if you can upgrade to 9.0.1 it might fix both problems.
I have a MainView which has an associated MainViewModel in my WPF application, assigned via its contructor.
App > start up uri > MainWindow.xaml
public MainWindow()
{
InitializeComponent();
var viewModel = new MainViewModel();
DataContext = viewModel;
}
My MainView holds as many as four nested views or child views who are hidden and displayed based upon the button that has been clicked on the MainView. So we toggling the visibility property vi a binding which gets updated via command bindings assigned to each button on the MainView.
Each nested View does not have an associated ViewModel, all bindings found on child views find their information in the MainViewModel. So binding system ends waling up the UI tree of the app to find out that the parent 'MainView' has an associated ViewModel.
So overall there is 'ONE' -> ViewModel. This seems to work fine and but as expected this VM has gotten to big and needs re-factoring. It holds information that contextually it should not. But this is a proof concept application. So i decided to keep it simple and make sure it was do-able.
PROBLEM:
When i tried assigning a empty view with an empty view model I noticed binding errors in the output window and as expected weird and broken behaviour. Which makes no sense ... Is there a more clear and concise way of letting WPF know how to handle any bindings it finds in a nested view control? I thought if each view's constructor assigned itself a corresponding VM as shown above, then it should work as this logically makes sense. Unfortunately all buttons on the MainView stop working when the corresponding view it is designated to switch on and hide the others has an associated ViewModel. On some buttons it works and the others it does not? This is really weird?
As mentioned in my answer above, the problem was that WPF binding system was struggling to to resolve bindings at run time. The main view has its associated view model instantiated and assigned via the Main View contructor and this pattern is repeated for all nested views that the MainView also houses.
By default, I tend to use the implied binding syntax which means that without explicitly specifiying a source the binding system will try to resolve the name you supply in the binding. So it's all implied and nothing is explicitly set!
Upgrading each nested view to have its own view model makes this auto discovery/resolution of bindings go a little crazy and I have not explicitly told the binding system where to find the property I am looking for hence the output window binding errors.
This leads to unexpected behaviour as the output window was telling that it was trying to resolve binding expressions in nested views --> viewmodels. When in actual fact that VM it is looking in, IS EMPTY!
So clearly the binding system is good when you do not explicitly set a source property inside the binding syntax. It is clever enough to find things on its own. In my case it needed some extra help, as it was unsure as to where to find things.
SOLUTION:
Remove the constructor declaration for the MainViewModel in the MainView constructor.
Scope in an xmlns for ViewModels namesapce into your MainView.xaml
Create a window resource inside the MainView .xaml
Give the resource a key.
Upgrade all your bindings in the MainView xaml file to include source property.
Give the source property a static resource binding that points to your ViewModel key value set up in step 4.
Only do step 6 for bindings who refer to the ViewModel that is associate with the MainView.
All nested views are to be left alone, they should handle their own bindingds in their own xaml files. The MainView simply instantiates them and places them onto the UI. For me this was the case, I did not have any more bindings concerning my nested views. All Bindings that lived on the MainView.xaml file referred to data in the MainViewModel.cs. This makes alot easier when viewing your problem.
For some reason the editor was being awkward so I chose to omit any sample code but the steps above are descriptive enough to follow the steps that I took. Above is what worked for me.
ANOTHER WAY OF SUMMING UP THIS PROBLEM
Most books teach the shorter binding syntax
What happens when more than one data context is available?
How is the binding system supposed to know how to resolve your short hand binding expressions.