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.
Related
I have a spark List in which I am adding custom components manually (without an item renderer). Everything is working fine except when I add hundreds of items in the list (based on several calculations), the render time increases to several seconds.
My questions are:
Does flex automatically delay the rendition of components that are added to a list?
If not then, how can I tell the spark list to only render the components once everything is added.
I hope what I am asking makes sense. I am pretty sure the render time is increasing because I have quite a few components inside the custom component. I just need a simple answer to my questions.
One more thing to know is that,
ActionScript 3 runs on flash player based on even-driven. It means that if you run a chunk of code in blocking, anything else, including rendering, will not be executed until the code ends.
This design sometimes causes issues: If a developer adds too much job in one blocking function, the player looks frozen and unresponsive momentarily. (If the code is an infinite loop, it stops until the player detects and throws ScriptTimeoutError, or possibly forever.)
However, for your question, yes, anything will be delayed until the adding job is done. Flex components doesn't basically split the job automatically.
Flex components are rendered in the list according to the Flex lifecycle: http://help.adobe.com/en_US/flex/using/WS460ee381960520ad-2811830c121e9107ecb-7fff.html
There are two reasons your List may be running slow, your components may not be following the Flex lifecycle correctly and the second because virtual layouts are not enabled on your List.
First the hard one:
Your first step should be to ensure you are following the correct phases in your custom components for commitProperties(), measure() and updateDisplayList(unscaledWidth:Number, unscaledHeight:Number).
So long as you are not calling any method named validateNow() on either your UIComponent subclasses or the LayoutManager then your components should follow this just fine.
The second may be that your list layout is not using virtual layout. This is enabled by default in a Spark List component but if you're overriding the layout you should ensure that useVirtualLayout is set to true on whatever layout you're using.
This is the property to enable it:
http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/spark/components/List.html#useVirtualLayout
This is what it does to speed up rendering many items in a Spark DataGroup component (which a List is):
http://help.adobe.com/en_US/flex/using/WSc2368ca491e3ff92-1483ec4a12136246e76-8000.html#WS685c4ccbb85d340c6617851e121d4b8abae-8000
I want to know if its a good idea to have an mxml file for each component, then inline these various components in one mxml file and able to communicate between these mxml files ?
For example I have a overView.mxml and in this, i inline the other mxml files which contains components like datagrid, another mxml contains may be a form. Will i be able to communicate to the grid data by accessing its id in the form mxml ?
Please let me know if my question is not clear. I will try to rephrase it.
Thanks so much.
Yes, this is a good idea. It's much better than creating one giant MXML or class that contains all of your functionality.
At the same time, it caries some overhead. To communicate between the classes (MXML files are just classes) you have to dispatch events. A parent component that contains child components, can set public properties of its child components (with or without data binding).
You should try to decouple your components as much as possible. Try not to write code where the child component is explicitly referring to the parent (ie: try not to use the parent property). Instead dispatch an event from the child component and make the parent listen for the event.
Regarding your example with a data grid and a form:
If these two objects will have a lot of interaction between them, it will be much easier to keep them in the same MXML file. This doesn't sound like a scenario where one is a parent component that contains a child component. Since these "siblings" are likely to communicate w/each other, it would be easier to have them in the same MXML file. However, if things get complex and the file grows to more than a couple hundred lines, you will likely benefit from separating them.
Let's say you plan to use the form component elsewhere in your project w/out the data grid, then it also makes sense to separate them.
Regarding your question: "will the form component be able to communicate w/the grid component by accessing it's id?":
Technically, yes, you could do that but only by tightly coupling your form component w/the grid component. The form component can use the parent property to go up one level and use the id of the grid. But since the parent property is typed as a DisplayObjectContainer you have to fool the compiler and you loose the benefits of strong typing (because the DisplayObjectContainer doesn't have a property that is the ID of your grid). So while this is possible, it's not good design and prevents you from reusing the form component elsewhere.
This tight coupling defeats the purpose of creating separate components. So you're back to either facilitating that communication through dispatching events, or putting the grid and form in the same document :)
TLDR:
You should generally be trying to create re-usable components. So I would generally lean in that direction. MXML files are just classes, all the usual things people talk about in object oriented programming apply.
In the examples for RobotLegs, it appears that mediators are used on every button/textArea, rather than on the custom component that contains these children. This would be very time consuming would it not?
From Joel Hooks InsideRia Example
Dependency injection works better with
unambiguous classes. What this means
is that by extending TextArea into our
new MessageView class, we are creating
a specific view component for the
dependency injection to act upon. This
is important if our application were
to have several TextAreas that served
different purposes. By dividing up our
classes in this way, we are clearly
defining the intent of the class and
allowing for the dependency injection
tools to do their jobs effectively.
No, don't mediate every child component. Your components should be organized into groups that perform related actions. In the examples the components are extremely simple and do not reflect what a real application would look like.
One rule of thumbs I use is thinking if that component needs any communication with the rest of the application, or if its only a part of a whole. Keep in mind that mediator are only intended to serve as a bridge between the view and the app.
For example, if I've a view with a form (asume a login form) I don't mediate all the child components (the textfields, the buttons, etc.) because it would be pointless and would have a proliferation of classes and objects on runtime. When I do the form I think, what does the view by its own? and what the other parts of the app should do with it?
When the user fills the form and clicks a button, the view dispatches an event (LoginRequestEvent, for this case), and then the mediator should redispatch that event, making the mediator very lean.
But with practice of the framework, you'll come up with this feel of what you shold mediate. For instance, in one app I mediate every item renderer of a list, and on other I mediate a view stack with two or three navigation contents.
Hope it helps
I've read in the flex developer guide that you sometimes need to override one
of the lifecycle methods like: commitProperties and updateDisplayList
but I've written a few flex apps without ever needing to implement them.
when do I need to override them?
First, I 100% recommend studying this presentation by EffectiveUI:
Diving Deep with the Flex Component Lifecycle
and this by Michael Labriola from Digital Primates:
Diving in the Data Binding Waters
They go into things you'll never find in the docs but that are super practical for understanding the Flex Component Lifecycle.
From my experience, the only time you need to worry about overriding core lifecycle methods is if you are creating components. I make a distinction between Application Views and the Components.
Components are things that need to be nearly perfect, highly optimized, and extremely versatile/abstract.
Views are things that you may only need in one Application, but could reuse if you so desired (LoginScreen, ContactForm, etc.).
Views, for the most part, are just adding things to the display list of a more generic component (Canvas, Group, Container, VBox, List, etc.). You, as a View/Application developer, don't really care about how the "dataProvider" creates it's itemRenderers, it just works.
Components are a different story though. When you create a component, you want it to fit perfectly into that system Flex has set up: the Component Lifecycle. It's pretty tough when you first try to build a component like they do, but after you wrap your head around it it's super easy. Here's how I think of the methods when I develop components:
createChildren()
Called once when component is constructed
Called top down. So if Panel calls createChildren, it's createChildren method will call addChild on all of it's children, which calls initialize, which calls createChildren.
If you created a custom component, say a StarRatingComponent, you might want to add 5 stars to the stage when the component is constructed. So you'd override createChildren() to do add stars to the component you're in. By default, though, all Container components in the Flex SDK add their children here (lists do it a bit differently), so you never have to do this if you're building MXML views or something not-to-be-extremeley-reusable.
The next 3 methods are called 1 frame after properties are set.
measure()
If the parent doesn't have any sizing (percent or explicit), it will need to be sized based on it's children's sizes. This can only happen from the bottom up (took me quite a while to really wrap my head around that).
If the parent has explicit or percent sizes, it skips this step.
You override measure if you want to:
Have measuredWidth or measuredHeight return a useful value. So if you build a custom CoverFlowContainer component, and measuredWidth/measuredHeight aren't set (because measure was not overriden), then if you don't specify any sizing on CoverFlowContainer, it would be 0 width 0 height. So instead, override measure and have it set measuredWidth to radius * 2 or something like that, and now you don't need to give it a size!
If the component does not have an explicit or percent size, measure will be used to size the component. Otherwise it's skipped.
commitProperties
Called after measure.
Applies all property changes (from setting properties on the component) to the component (they were stored in private variables for that first frame).
Called a frame after initial property settings.
This is the most important method to override in my opinion. So for your CoverFlowContainer, say you set the hypothetical distance, gap, selectedItem, and tilt properties. When you set them, store them in private variables. Flex will wait a frame, and call commitProperties. In your overridden commitProperties, you can then say layout.updateEverything(selectedItem, distance, gap, tilt); so to speak. So this is the method you override to make all property changes be applied at once.
updateDisplayList
Called after commitProperties
Called top down.
You only override this to set visible properties on the component, such as setActualSize, graphics, etc. But by now (because of `commitProperties), you have all your required variables to update the display set to the right values.
Overall
So from my experience, I worked a lot with these lifecycle methods when creating a component library for things I would use in a million projects:
TitleWindow (my own version)
View3D (for Away3D/Papervision)
Tree and Stack for Flex 4
TextArea (with prompt, expandable, etc.)
ToolTip (easier to skin tooltip)
I needed to make sure everything was updated and rendered perfectly according to the lifecycle. Reading and understanding the Flex 4 Spark Source Code really helps clarify when to override these methods. As does the Openflux Source Code (very simple, clear alternative to the Flex Framework. Not as feature rich so it shows how to bare-bone override those methods to accomplish some pretty advanced things).
When I develop applications and make things like AdvertismentView, MenuView and LoginView, I don't ever think about it because all the components I'm using have already solved those problems (ViewStack, Group, List, etc.). I'm basically just setting properties they've defined and updated in their own commitProperties override.
The only time I would start overriding lifecycle methods in a View would be when I need to access custom variables from outside the view. So say I had a custom RichTextEditor and I created some properties called showFontControls and showStylePanel. When I set those variables, I would probably do what they described in the Data Binding Presentation: accessor sets private variable and calls the invalidation methods, lifecycle methods execute a frame later and I have overridden commitProperties and updateDisplayList to show those panels and fonts. But in practice, that's probably overkill because it wouldn't offer that much of a performance gain for the amount of work it would take. I'd just set up some binding to a visible property in that case. Nevertheless....
The best thing to do to really get into this is to just download the Flex SDK Source and see what they're doing.
Hope that helps.
Lance
Here's another presentation by Deepa (from the Flex framework team) that goes over a lot of the same framework methods, including a nice explanation of why the whole invalidation model exists to begin with:
http://tv.adobe.com/watch/max-2008-develop/creating-new-components-in-flex-3-by-deepa-subramaniam/
What is the best way to render to a UIComponent which hasn't been added to the stage? (I'm using UIComponents as renderers for objects, and want to render new copies for image export, filtering, etc.)
Two strategies I've seen/used so far include realizing the component to ensure it calls all the lifecycle methods:
Add the component to Application.application, render with BitmapData.draw(), remove component. This is similar to what I've seen done for printing unrealized components as well.
Add the component to a pop up window, render with BitmapData.draw(), dismiss popup after rendering complete.
I believe both of these just rely on the UI not refreshing while the current thread/event is executing, though (1) could also rely on the component being realized out of view.
Is there a better way?
What I've used in the past with much success is the following:
Create a new instance of your component
Add an event listener for FlexEvent.CREATION_COMPLETE
Set visible=false on the component
Add the component as a child of the main Application
When the component is created, the event listener function will be invoked. The rest of the logic should be put in / invoked from your event listener function
Remove the event listener you added in step #2.
Use ImageSnapshot.captureImage() or captureBitmapData() to capture the visual representation of the component.
Remove the component from the main Application
Process the image data as you need to.
I've used this to snapshot various Flex charting components for use in PDF's generated on the server side. After getting the BitmapData I use the PNGEncoder or JPEGEncoder classes to compress the data, then encode it in Base64 before uploading to the server.
I'm pretty sure you can use the draw() method in BitmapData without having your component on the DisplayList.
For example is use it when I need to modify images I load with the Loader Class. In the init handler I create a BitmapData instance and draw the Bitmap from the loadInfo.content property, then copyPixels() or whatever I need to modify the loaded image
So much of a UIComponent's layout can be tied to it's context. This is especially true for a lot of its derivatives (e.g. HBox) since the fluidity of the layout is tied to it's parent's size and the number of siblings sharing its parents space.
Additionally Flex can be a real pain to get to visually update. Often critical render functions aren't done synchronously ... there are callLater, callLater2 and other hacky approaches that make dealing with the auto-magical layout properties of UIComponents a major headache. Not even calling validateNow or updateDisplayList can guarantee that the layout will be correct on the current frame (instead of a few frames in the future).
I suggest the best thing you can do is not use a UIComponent and try and use a Sprite or other.
Your approach to attach it but make it invisible (alpha = 0, mouseEnabled = false, mouseChildren = false) is decent. You should listen for the FlexEvent.CREATION_COMPLETE callback before you are certain it is properly laid out. Then you can bitmapData.draw it and then remove it from the stage. If you must use UIComponents then I know of no better way.
You can call the lifecycle function manually before using the BitmapData.draw(). Do the following.
createChildren().
commitProperties().
updateDisplayList().
bmd.draw().
The first 2 steps are not 100% necessary, you can put all codes into updateDisplayList(). Because you invoke the function manually, you don't have to worry this is invoked by Flex framework many times.