Fix to - Only one operation can be active at at time #598

[vagrawal1986]

Fixes # .

1. src/Media.Plugin/Android/MediaImplementation.cs
2. src/Media.Plugin/Android/MediaPickerActivity.cs
   Changes Proposed in this pull request:
   Following scastria comment -

#598 (comment)

"The cause is pretty simple. The media picker uses TaskCompletionSource to turn a callback driven API into Task async/await style. but the code adds a check to make sure that only 1 TaskCompletionSource is active at one time. "
"So whether you click the button twice or do my workflow, in both cases TaskCompletionSource is not null the second time and the exception is thrown."

If we null out the completionSource onDestry of the MediaPicker activity, we can get rid of the bug

[vagrawal1986]

@motoko89 - Here are the steps for this -
This bug is hitting us too but with a different workflow:

1. Launch app
2. start media picker
3. click home button
4. resume app by clicking icon on phone desktop (if you use the task switcher, it works)
5. app resumes but media picker is gone
6. start media picker
7. crash with "Only one operation can be active at at time"

Now as soon as you click the hime button, destroy on the Media activity will get called as its not the Main activity in my case. Main activity is my App, where I am using the Media plugin, which has a MediaPickerActivity.

[jamesmontemagno]

There were a lot of changes in the multi-select gallery part, will need to resolve some conflicts or make a new PR here

[vagrawal1986]

@jamesmontemagno
Thanks for looking into this. All conflicts resolved, would greatly appreciate if this can be merged.
Thanks
Also,
I am very new to Github community and this is my first pull request, so pardon any silliness :)

[Trevonious]

@vagrawal1986 Do you think this fix would apply to the issues with clicking outside the popup in iOS (see #666)? It looks like the original author of the multi-select feature was seeing the same issue as me, but it seems he thought it was handled (#598 (comment)).

[vagrawal1986]

@Trevonious
The fix I put in only caters droid only as I did not face any issue with iOS at least before multi-select. I have not investigated clicking outside issue on iOS for multi select. But I think this fix should handle the android part of the bug.