A MonoDroid MvvmCross experiment in autocomplete

I got asked a question about implementing Mono for Android/MonoDroid autocomplete support on Jabbr - http://jabbr.net/#/rooms/mvvmcross

This then turned into a question and answer on StackOverlfow - http://stackoverflow.com/questions/10550829/autocomplete-mvvm-and-java-castings-without-using-java-lang-object-on-viewmodel

After some hacking at a Google Books API sample, then I created a sample - see the video at:

• YouTube - http://www.youtube.com/watch?v=l9JqlA_YZ4k

This example works using a new alpha databinding Autocomplete class and adaptor within the MvvmCross framework. It may be that these classes never actually make the cut to be full time framework members - in which case they can live in some external library instead.

The basic functionality uses databinding on 3 new properties:

• PartialText - which is a partial text string - sent from the View to the ViewModel
• ItemsSource - which is the set of current items available for the supplied PartialText - sent from the ViewModel to the View
• SelectedObject - which is the current selected item - sent from the View to the ViewModel

You can see these setup in the binding xml as:

<Mvx.MvxBindableAutoCompleteTextView
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  local:MvxItemTemplate="@layout/listitem_book"
  local:MvxBind="{'Text':{'Path':'EnteredText','Mode':'TwoWay'},
  'ItemsSource':{'Path':'AutoCompleteSuggestions'},
  'PartialText':{'Path':'CurrentTextHint'},
  'SelectedObject':{'Path':'CurrentBook'}}"
    />

Note that because of the Android threading model it is essential that every change in PartialText is met by an eventual signalled change in ItemsSource - and this should be a single change in object collection rather than lots of small changes.

The code for this initial sample is in: https://github.com/slodge/MvvmCross/tree/master/Sample%20-%20SimpleDialogBinding/SimpleBinding/DroidAutoComplete

Note that this sample uses "simple binding" rather than the full Mvx framework and as a result there is slightly more threading to worry about in the ViewModel.

The binding view and its adapter are not simple code to follow - the binding code is fairly abstract in nature - but they can be found in:

• MvxBindableAutoCompleteTextView
• MvxFilteringBindableListAdapter

  

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If you are doing anything network-linked then in the long term I believe it may be better to implement a new autocomplete view rather than to use the built into Android today!

And if you are doing an autocomplete sample, then I highly recommend the google books api - it's simple to use and fab for demos :)