Hi Narcís,
In my code I have:
[Application]
public class MyApplication : Application
{
...
public static readonly MyApplication theApp = new MyApplication ();
...
public MyApplication (IntPtr intPtr)
:base(intPtr)
{
}
...
}
In various places its properties get referenced like:
MyApplication.theApp.layout
If you put tracing inside the constructor for MyApplication youll see the
object being constructed when the app starts, but then also again if Android
closed the app for its own reasons (or if there was a crash) and later on
re-starts it without the user initiating things.
In your case that might work better than creating an instance of
MyApplication which isnt a singleton. But you also need to bear in mind
that MyApplication might get constructed at strange times:
With the Activity lifecycle the activities exist independently of each other
and are OnCreated by Android without you being able to have a stack like
you do on Windows with ShowDialog. Hence if your current activity is
OnDestroyd by the OS because of, say, memory issues then the next youll
know about it will be an OnCreate and, quite possibly, your MyApplication
constructor will get called again at that point, And youll need to
re-initialise things (eg. data access layers or background threads) that you
may be holding at this global level.
(In the same way, you can have a stack of activities which look as though
they all exist at the same time and the stack unwinds as activities are
Finished, but really the only activity you can rely on is your current one,
any others may well get destroyed and will get re-created just in time by
the OS to process OnActivityResult etc. So you cant rely on any references
to those other activities.)
Anyway, thats my understanding at least. These are all things that were a
culture shock to me as a Windows programmer, maybe theyre obvious to
everybody else!
Cheers,
Andy
From: monodroid-boun...@lists.ximian.com
[mailto:monodroid-boun...@lists.ximian.com] On Behalf Of Narcís Calvet
Sent: 27 July 2011 14:49
To: 'Discussions related to Mono for Android'
Subject: Re: [mono-android] Getting objects from an intent
Hi Andy,
Following your advice Im using the custom application below. It has a
public property (layout) which I use to add to the main Activity. The
problem is this property is always null there. Application is bein used in
main Activity OnCreate event like this:
var ctrl = new MyApplication();
SetContentView(ctrl.layout);
MyApplication implementation:
[Application]
public class MyApplication : Application
{
public RelativeLayout layout { get ; set; }
public MyApplication(IntPtr handle)
: base(handle)
{
}
public MyApplication()
: base()
{
}
public override void OnCreate()
{
base.OnCreate();
MyImageView i = new MyImageView(this.ApplicationContext);
MyImageView i2 = new MyImageView(this.ApplicationContext);
layout = new RelativeLayout(this);
layout.AddView(i, new
RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.FillParent,
RelativeLayout.LayoutParams.FillParent));
RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(400,
400);
lp.LeftMargin = 100;
lp.TopMargin = 100;
layout.AddView(i2, lp);
}
}
Do you have any idea how should I use this property in the parent Activity?
I tried doing the same in Java for Android and cant even get the onCreate
event firing there.
Best Regards,
Narcís Calvet
Steema Software
http://www.steema.com <http://www.steema.com/>
http://twitter.com/SteemaSoftware
https://www.facebook.com/SteemaSoftware
From: monodroid-boun...@lists.ximian.com
[mailto:monodroid-boun...@lists.ximian.com] On Behalf Of Andrew Sinclair
Sent: dimarts, 19 / juliol / 2011 14:01
To: 'Discussions related to Mono for Android'
Subject: Re: [mono-android] Getting objects from an intent
Narcís,
You can derive from Android.App.Application, this will give you a singleton
class which can hold global application state. For such a class you need to
use the [Application] attribute - this will add the appropriate entry in the
AndroidManifest.xml.
Storing the instance of an activity doesnt seem much use in Android because
activities are created and destroyed regularly by the system in accordance
with the activity lifecycle. So if you want to access a property of one
activity from another activity then theres a very good chance that the
target activity will be invalid.
This might be different with activity groups, I havent used them, but in
general Ive found it best to store data in an instance-independent manner.
The same things applies with Views. Suppose you had 2 views within an
activity that both cause another activity to be shown, and you wanted to
remember which view had triggered this new activity. Within Windows you
might have a member variable of the calling activity called _triggeringView
and youd access this when you returned to the original activity. With
Android thats no use because you have to assume that the original activity
will be destroyed during the whole process. One way around this is to store
something like triggering view was the 2nd view at the application level
or as part of the saved state bundle in the activity. So youre just storing
an integer.
Clear as mud? I hope it helps anyway, the implications of the activity life
cycle are very far reaching if you are porting an application from, for
example, .NETCF.
Andy
From: monodroid-boun...@lists.ximian.com
[mailto:monodroid-boun...@lists.ximian.com] On Behalf Of Narcís Calvet
Sent: 19 July 2011 12:28
To: 'Discussions related to Mono for Android'
Subject: Re: [mono-android] Getting objects from an intent
Searching a little bit and looking for whats available in IParcelable it
seems it is not complete in Mono for Android so I guess I should discard
this option. Any other ideas?
Thanks!
Best Regards,
Narcís Calvet
Steema Software
http://www.steema.com <http://www.steema.com/>
http://twitter.com/SteemaSoftware
https://www.facebook.com/SteemaSoftware
From: monodroid-boun...@lists.ximian.com
[mailto:monodroid-boun...@lists.ximian.com] On Behalf Of Narcís Calvet
Sent: dimarts, 19 / juliol / 2011 11:04
To: 'Discussions related to Mono for Android'
Subject: [mono-android] Getting objects from an intent
Hello,
I have created a custom activity which I use in an ActivityGroup using
Intents. How can I get the instance of my custom activity the intent has
created to be able to use its properties and methods? I read I may need to
use Serializable or Parcelable interfaces but havent succeed on this so
far. Monodroid examples on this would be great!
Thanks in advance.
Best Regards,
Narcís Calvet
Steema Software
http://www.steema.com <http://www.steema.com/>
http://twitter.com/SteemaSoftware
https://www.facebook.com/SteemaSoftware
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