I understand from documentation and several related StackOverflow posts that window.parent, if there is no other parent, will self-reference and thus never be undefined.
I can't seem to find a decent reason as to why this is. JavaScript does have its idiosyncrasies, but this one just seems odd.
MSDN simply states that
If the current window doesn’t have a parent, i.e. it occupies the whole browser window, Parent returns the current window’s Window object.
MDN states
If a window does not have a parent, its parent property is a reference to itself.
And the W3 standard itself
The value of the parent attribute of a Window object MUST be the parent document's Window object or the document's Window object if there is no parent document
I've not seen other languages acting like this, what reason is there for this self-referencing design? Wouldn't 'null' or 'undefined' make for a more obvious situation when you hit the topmost element in a window?
So, why?
When working with iframes, developers often automate processes which navigate through windows. While the algorithms at their core will consist of the same basic logic, the conceptual approaches will differ.
Instead of working in a parent-children manner, sometimes the developer will craft the system in such a way that it will seem not to look for the parent, but simply for the right window to use. The one that controls (not necessarily holds) the area where the code is currently running.
In the case of such approaches, it would be conceptually weird for the program to return "false" or "undefined" when asking it a refference to the "right" window, because there must be one.
For instance, Bob is programming:
Bob: I embedded an iframe! Alright, let me just play around with the window that contains my entire iframe (not the window of the iframe itself)
Bob: What? Null? But I don't get it, my iframe is up & running, how can there not be any window which controls it?
I'm just saying that window.parent may not be meant to literally and strictly get the parent from the DOM (like .parentElement does), but more like to point to the window which absolutely wraps not only your script, but also everything else that wraps it at lower levels.
In the case of the topmost window (where your script is being executed), that statement may return the same window because, not having any oher window more important than it, it simply becomes 'the right one' to use when looking for the superior container.
I hope I make some sense.
I would say that this helps with window communication. When loading third party content, it might leverage window.parent.postMessage as it's form of communicating with it's implementation context, but it might be implemented with no parent window. An html page loading content in an iframe would have its own window as the iframe windows parent, but content loaded into something like a browser plugin such as an electron webview would have no parent window so the postmessage would fail and the implementing context would not be able to listen for that event. So basically it just allows for a safety net to allow devs to always be able to use window.parent because they might not know if their code will be running from window.top or not.
I assume this is just unfortunate naming. That property could have been better named something like 'parentOrCurrentWindow'.
If what you want is 'parent or current window' then being able to access that as just 'parent' makes your code a little shorter. And if you know that is so then it does not matter much. You could say it is better to get hold of SOME window than null.
But note this has nothing to do with JavaScript the language. This is about the DOM-model implemented by browsers. The DOM model could be improved to include two properties 'parentOrCurrent' and 'parentOrNull'. And in fact you could assign those variables in your own code to make it clear which one you are talking about.
Related
https://github.com/brianchance/MvvmCross-UserInteraction is a very nice plugin for showing cross platform Alerts!
But for this question, can we assume it can not use a UIAlertView (or some other top level MessageBox type call on other platforms) but needs to show a Message within a given subsection of the screen (i.e. on IPhone you would need to supply a UIView to the plugin which it will use to show the message within).
So, how would you set this up so the ViewModel knows what View to use as its display container?
As a specific example, if I wanted an Error Service, as so -
public interface IErrorPFService
{
void Show();
void Hide();
void SetErrors(List<Error> errors);
}
and I create a platform specific implementation for it.
If I inject this into my ViewModel so it can control Error Show/Hide/Set how do I tell it the UIView (or equivalent) that I want my Errors to show within?
Can I just expose the IErrorPFService field as a public property and do -
MyViewModel.ErrorPFService = new ErrorPFService(View);
in my ViewDidLoad ...
Or is this coupled incorrectly vs Mvvm Practice?
I would expect the ViewModel to subscribe itself to the ErrorService.
When receiving a message it would expose it in a collection(?) and the View would bind to that collection.
This way the View is unknown to the service and the ViewModel has the chance to influence the View contrary to your solution.
It would help if you could give an example for the scenario you are describing.
Sometimes, the way you visually want to display something might not be the best way, so if it's possible for you, you might find a different and simpler way, which spares you from having to find a solution regarding what you are describing.
Generally, I always do the best I can to avoid the idea of having to actually pass a 'view' or an abstraction of it, from the view-model to view. Also, cross-platform wise, things can work very different in terms of UI interaction. You can find yourself in a situation when things are complicated just because UI works differently than what you expected.
But let's try find another perspective:
At any given point, the view knows what data \ feature it's displaying. So when you are calling from the view-model an user interaction action (by a service, property change, event, etc) the view should 'expect' it.
For example, the platform specific user interaction implementation is able to get the currently displayed top-view and interact it in a platform specific manner or based a relationship. In your example, the message-box can be displayed in a specific sub-view of the top level view.
In advanced scenarios, I guess you could try to create a cross-platform approach for this, but you should try to put in balance all the abstraction you want to create just for that. Think about doing this as a plan ... Z. If possible. Again, giving an example might help.
GWT's Editor framework is really handy and it can not only be used for editing POJOs but also for read-only display.
However I am not entirely sure what the best practice is for doing inline edits.
Let's assume I have a PersonProxy and I have one Presenter-View pair for displaying and editing the PersonProxy. This Presenter-View should by default display the PersonProxy in read-only mode and if the user presses on a edit button it should allow the user to edit the PersonProxy object.
The solution I came up with was to create two Editors (PersonEditEditor and PersonDisplayEditor) that both added via UiBinder to the View. The PersonEditEditor contains
ValueBoxEditorDecorators and the PersonDisplayEditor contains normal Labels.
Initially I display the PersonDisplayEditor and hide PersonEditEditor.
In the View I create two RequestFactoryEditorDriver for each Editor and make it accessable from the Presenter via the View interface. I also define a setState() method in the View interface.
When the Presenter is displayed for the first time I call PersonDisplayDriver.display() and setState(DISPLAYING).
When the user clicks on the Edit button I call PersonEditDriver.edit() and setState(EDITING) from my Presenter.
setState(EDITING) will hide the PersonDisplayEditor and make the PersonEditEditor visible.
I am not sure if this is the best approach. If not what's the recommended approach for doing inline edits? What's the best way to do unit-testing on the Editors?
If you can afford developing 2 distinct views, then go with it, it gives you the most flexibility.
What we did in our app, where we couldn't afford the cost of developing and maintaining two views, was to bake the two states down into our editors, e.g. a custom component that can be either a label or a text box (in most cases, we simply set the text box to read-only and applied some styling to hide the box borders).
To detect which mode we're in, because we use RequestFactoryEditorDriver (like you do), we have our editors implement HasRequestContext: receiving a null value here means the driver's display() method was used, so we're in read-only mode. An alternative would be to use an EditorVisitor along with some HasReadOnly interface (which BTW is exactly what RequestFactoryEditorDriver does to pass the RequestContext down to HasRequestContext editors).
Yes,Presenter-View pair should be. But Here two ways to achieve this feature if you like to go with:
1) Integrate Edit/View code design in one ui.xml i.e.Edit code in EDitHorizonatlPanel and View code in ViewHorizontalPanel.The panel has different id. By using id, show/hide panel with display method. if getView().setState() ==Displaying then show ViewHorizontalPanel and if getView().setState()==Editing then show EditHorizontalPanel.
2) Instead of using labels, Use textboxes only. set Enable property is false when you need it in view mode otherwise true
You have created two Presenter/view but I think if Edit/View function has similar code so no need to rewrite similar code again and again for view purpose.
If a big project has so many Edit/View function and you will create such type of multiple View/Presenter than your project size become so huge unnecessary.
I think that whatever I have suggest that might be not good approach but a way should be find out which help to avoid code replication.
I have to maintain a part of an old Windows VB6 project (so, don't tell me to migrate-it to VB.NET). This program embeds the well known webbrowser control (IE) in which it loads local HTML files (containing different stats, but doesn't matter). Knowing we don't want any scroll bar in the web browser view (even if HTML page is longer than the webbrowser window, we just need to see what it's on top), we manage DOM on DocumentComplete event like this :
Private Sub wb_DocumentComplete(ByVal pDisp As Object, URL As Variant)
wb.Document.documentElement.Style.overflow = "hidden"
ProcessWithDStats
End Sub
All sounds right and the vertical scrollbar well disappear, but now, I need to add some stuff in the ProcessWithDStats sub (a big sub calling a lot of functions) which need to be sure the previous DOM operation is totally completed (I mean : scrollbar hidden and it's content re-justified accordingly to this new width w/o scrollbar).
So, how to do ?
At this time, ProcessWithDStats is executed before DOM management really finish to be rendered !
Until now, here are my attempts :
I've tried to add a scrollbar testing (comparing doc width and browser client area one) between the two lines, but it doesn't work : test is OK, but reflow of text (because of this change of width when scrollbar disappear) has not enough time for being applied before ProcessWithDStats is engaged.
I've tried to Sleep(), but it locks entire program (webbrowser rendering included)
Well is there a way to wait for real application of the given DOM management in this WebBrowser control ?
I mean something like :
Do
Doevents
Loop Until [DOM modification and rendering completed]
you need to do this... at the very least.
Do
Sleep 100
Doevents
Loop Until wb.Busy = False And wb.ReadyState = 4
On your version the .Busy may be called .IsBusy but are the same thing.
Also, there are additional things you should do if you want to truely know if a browser is done loading, read some of my previous answers if you want to know more, or need more accuracy than the above, but what i have included for you is for sure a much better solution than you currently have. Let me know if you need it to work on 100% of websites or just a select few, if a select few than this simple method may be enough.
Let me know hwo it goes anyway, cheers.
I read this
"
It used to be that Android would use a single pass to process
RelativeLayout-defined rules. That meant you could not reference a widget
(e.g., via android:layout_above) until it had been declared in the XML. This
made defining some layouts a bit complicated. Starting in Android 1.6,
Android uses two passes to process the rules, so you can now safely have
forward references to as-yet-undefined widgets.
"
I do not know what is the problem maybe is eclipse problem, but even I use 2.3 I still have problems when I reference some view that is not declared jet so for me it seems like android doesn't uses two passes to process the rules for relative layout.
note: I always use #+id/widget_name when I declare the widget and #id/widget_name when I reference that widget from other widget. I have noticed that I can use #+id/widget_name even when I just want to reference that widget. I guess that is wrong but why sometimes is works without any complaints ? In my opinion one widget should be allowed to be declared only ones...
My questions is is really android uses two passes ? and I need some guidelines (best practices) for working with relative layouts
I am little confused about how this relative layout parings are made, so any explanations are welcomed
Thanks
#+id/name creates a new id, if it doesn't already exist. #id/name references an existing id, and will never create one.
I'm not sure if you can use #id/name before #+id/name in the same file. If not, I can think of two workarounds:
Always use #+id/name.
Define all id's in the ids.xml file, and always use #id/name.
This is general information on how Android draw views.
I think that Android passes twice through all the view, but it doesn't pass through each single view once. So if you have a reference from one xml to another it will always work fine, but if you have references inside a single xml you must be carefull to order the elements in the xml correctly. For example, I have view1 and view2 in my RelativeLayout. If I want to refer to view2 from view1 I must declare view2 before view1.
I am trying to bring my secondary form to the Foreground, however when I do
MyForm.Show; // It may be hidden, therefore show it first
SetForegroundWindow(MyForm.Handle);
my Main Form appears aswell. The only way I can prevent that is to do MainForm.Hide; but I got to avoid that.
The idea is to have my secondary form appear on top of another application, without my Main Form having to do so as well.
If you consider to make another application for this functionality, then you may also consider the following compromise: minimize the MainForm to the taskbar (rather than hiding it) to prevent it popping up when activating another form.
If so, then try this answer. It does add an extra icon to your taskbar for the secondary form, but I guess that'll be no problem since a different application would either. However, if the MainForm is nót minimized but obfuscated by other windows, activating the secondary form wíll also popup the MainForm, just like you are experiencing now.
And for the completeness of this answer's sake, but not by any means meant as advice: this answer describes a (somewhat experimental) construction to make fully independent windows. The little time I tested that solution, it seemed to work, but be prepared not counting any longer on the full/default functionality of the VCL.
Try settings the state of the form to fsAlwaysOnTop.