Just to get the answer on the mailing list:
http://stackoverflow.com/a/8221373/83444
On Nov 21, 2011, at 1:51 PM, Paul F. Johnson wrote:
> I have a standard winform which looks like this (in part)
>
> namespace marker
> {
> public class xmlhandler : Form, Isettings
> {
> public xmlhandler(common data)
> {
...
> where common is just a class containing a pile of variables.
>
> Is this possible to do within the mono for android framework (with the
> exception of finding the path) and if it is, how is it done?
Can you provide an `Activity` constructor which takes parameters? Yes. Would it
be at all helpful? No, because Activities are started through
Context.StartActivity() [0], which provides no mechanism to invoke a
non-default constructor.
The "Android Way" to transfer data between Activities is to use the Intent
"extras" mechanism, e.g. Intent.PutExtra(string,string) [1] and
Intent.GetStringExtra(string) [2], which introduces it's own set of problems:
1. Intents are also an IPC mechanism (as an Activity may actually reside in
another process -- this is by design), so you're restricted to types which can
be marshaled across process boundaries.
2. `String`s, `int`s, and other builtin types are supported, but aren't exactly
"high level" objects.
3. "Higher level" objects are supported through the android.os.Parcelable [3]
interface, but (a) it has a "marshal by value" semantics, so isn't useful for
sharing read+write data between activities, and (b) Mono for Android doesn't
currently support implementing this interface [4].
So how do you share data between Activities? By punting.
* Place the data onto an Application[5] subclass. This will be accessible via
the Context.ApplicationContext [6] property, and can store process-global state.
* Use some other `public static` field within your process to contain the
shared information.
* Provide a ContentProvider [7] implementation which will store and provide the
desired data when prompted.
* Sqlite?
* Serialize to a string and transfer the sring
* etc.
The launched activity can then use the Bundle parameter passed to OnCreate() to
extract the Intent data.
- Jon
[0]
http://androidapi.xamarin.com/?link=M%3aAndroid.Content.Context.StartActivity(Android.Content.Intent)
[1]
http://androidapi.xamarin.com/?link=M%3aAndroid.Content.Intent.PutExtra(System.String%2cSystem.String)
[2]
http://androidapi.xamarin.com/?link=M%3aAndroid.Content.Intent.GetStringExtra(System.String)
[3] http://developer.android.com/reference/android/os/Parcelable.html
[4] http://docs.xamarin.com/android/about/limitations
[5] http://androidapi.xamarin.com/index.aspx?link=T:Android.App.Application
[6]
http://androidapi.xamarin.com/?link=P:Android.Content.Context.ApplicationContext
[7] http://androidapi.xamarin.com/?link=T:Android.Content.ContentProvider
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