I have a Flex application with three different views. Only one view is shown at a time, and the choice of view depends on what part of the application the user is working with. If it had been an ordinary HTML webapp I would have created three different HTML-templates/pages for each view.
What is the recommended way to handle such application views in Flex?
The behavior you want is usually accomplished by using a ViewStack component. In MXML you declare child containers for each view you want, but only one gets shown at a time. You can change which one is shown programmatically whenever conditions are met by setting selectedIndex on your ViewStack. By default the first child container is displayed when run. Another approach is to declare and use states in your container and change currentState whenever you need to change the view. Hope that helps.
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What would be the preferred (recommended) way to rearrange the components of a QML UI on an event such as a button click?
I do have designed a UI consisting of a bunch of custom components, each of them is bound to a (C++) model. I use anchors to position the components in the ApplicationWindow.
On a button click, I want to add an additional component which, due to its size, makes it necessary to rearrange the existing components. Actually, the button could be understood as switching into a different mode such as the Debug view in an IDE (think of Eclipse).
My goal is to keep the components in a consistent state between views and make the switch as fluent as possible.
I could think of these options:
Design two different views, and use a Loader or State to switch between them. As initializing the models takes some time, they should remain not be deleted during switching. I think, setting them as ContextProperty of the QMLApplicationEngine should take care of that.
Do a lot of rearranging in the onClicked()-Handler of the button. Probably the worst solution but does not require to reinitialize the components and models.
I think the most elegant solution would be to initialize the components in a some kind of container (or model) and then assign different layouts to this container on button click. But I have no idea, if this is possible and how to achieve that.
Edit: I followed approach 1. by using the StackLayout. It works basically, but it seems as if the invisible UI is still running in the background and consuming resources (e.g. requesting Images from my QQuickImageProvider).
Using a Loader eliminates this problem as it destroys the previous UI on every change of the source property. What I do like about the StackLayout however is that it preloads all UIs on app startup. So the transitions are smoother compared to the Loader. Is there a way to disable the invisible UIs?
Your option (1) is the one giving your the most flexibility, since you have two entirely separate UIs depending on state.
As you already discovered yourself this requires keeping all relevant state data in a way that is accessible by both UIs, e.g. in C++ or in globally accessible QML/Script objects.
I would go for that if you envision any more changes or tweaks than just rearranging elements.
If you are sure that rearranging elements will be sufficient, have a look at QML states
It is a bit like a combination of your options (2) and (3).
The state setup allows you very locally to define anchors and other properties for each element depending on a named state.
The button's signal handler then only needs to change which of the states is active, by assigning one of the names to the respective state property.
how to naviaget one mxml page to another via action script
the navigatTourl() method used for webpages but, if want to navigate another mxml page mean how to show
When creating a Flex Application, the page analogy does not work very well. In an HTML site, each page is a self contained entity with no real relation to any other page. However, a Flex Application is a single self contained entity; and that entity can have lots of screens, or views.
To navigate between views in a Flex Application there are a lot of ways. Here are three approaches:
You could use States
You could use a Navigator container, such as a ViewStack or a TabNavigator.
You could toggle the visible property of your UI Components.
Generally, the first two options would be used for massive changes. The third option would be used for minor changes.
When I try to access the hidden TABs of my tab navigator control in action script, it returns a null error. But it works OK if I just activate the control in the user interface once. Obviously the control is not created until I use it. How do I make all the tabs automatically created by default ?
<mx:TabNavigator creationPolicy="all"/>
That should do it. Deferred instanciation is a feature, but sometimes it is a hassle.
The Flex framework is optimizing creation be default (creationPolicy="auto") so if you have a configuration dialog with a lot of tabs, for example, and the most useful tab is the first one, your application does not spend time and memory initializing the tabs that the user never sees.
This makes a lot of difference when dialogs like this never release, and is a good default to go with.
One thing to look at is using a private variable in your dialog/form instead of pushing the data to the control on the hidden page. This style treats the whole form as if it were a component, which it sort of is. To repeat: the MXML form/dialog/canvas is a class, and it can have data and methods in addition to containing other components.
Cheers
On a side note, I've run into the deferred-loading policy in a multi-state application, and circumvented it by forcing all elements to be included and invisible in the initial state. Something to consider, but only as a hack.
I have an MXML component in a website that I am reusing in a few different screens.
Based on what the user clicks, the component initializes a few values and starts playing media.
Now if I click through the site, and I play media in screen 1, the component initializes fine and plays the media.
If I then go to screen 2 and play the media, the component initializes twice. Once for screen one, and once for screen 2.
When I then go to screen three, it will start initializing three times.. So it is creating a new instance of the MXML component for each screen!!
How can I make sure that the MXML component only initializes for the screen that I need it to initialize for?
What I really want is that this component always has just one instance throughout the whole application. Is it possible to make that MXML component into a Singleton, so that I always have one instance of that MXML in my application?
Can you explain this a little more indepth? What do you mean by "screens"? It sounds like you have your component nested in some sort of view stack, and that your screens are different sections in the view stack, but it's hard to tell here.
Regardless, I think the solution is to abstract the part of your component that you want to be a singleton from the view. Flex initializes objects in view stacks in a lazy manner by default, but this can be overridden using the creationPolicy property on the ViewStack object. It sounds like your creationPolicy is initializing children as you access them, and something in your component code is causing other instances of the same object to re-fire some initialization code when others are created (possibly in your experimenting for an MXML singleton.)
To truly achieve your desired effect, you should probably just write a bit of actionscript that intelligently re-parents the display object you only want to be created twice. The idea of a "singleton" doesn't make as much sense when we're talking about view objects on screens - to have it displayed in many places, you need many instances, and the process of re-parenting is slightly more complicated than the singleton pattern, so you'll need to do a bit of creative logic around that.
Hope this helps - again, please feel free to post some more source code if you want a more specific response.
Why don't you make the component into a module and use it that way. You Load and/or Unload a module and use it where ever you like! in just calling it as a single item! and you have very much less overheads in your application.
In my flex project i used one option like Link button . If i like it will be open new page
contain more information and components . Which container is suitable one ?
Where is used viewstack and stages ? if you know please explain it . or refer me
With states you can have objects in each state with the same id - this cannot be done with a viewstack. Usually states are used when a group of objects are shared amongst the different "states" or "views". So for example you can have a textinput in each one of your states and give each one the same id of "username". When you reference the "username" id it will use the object in the currently enabled state. If you try to do this with a viewstack it will throw an error saying you've defined an id of "username" multiple times.
So as a wrap up... use states when you're adding or removing components from a set of components shared throughout each state. Use a viewstack when each view is different and do not share components.
Use states when your views are very similar and only differ based on a few controls or components. If you have too many AddChild / RemoveChild elements it becomes more difficult for a developer to follow your code.
A ViewStack also supports deferred instantiation through the "creationPolicy" attribute. This means that only the first Container in a ViewStack will be initialized when the ViewStack loads. This can really speed up load time of your application if you (A) have a lot of children in the ViewStack or (2) the children are large / complex components.