Intercepting SimpleCursorAdapter data #androiddev

Normally when you create a SimpleCursorAdapter for a ListView, you specify a one-to-one mapping of the columns from the DB and the views where you want them to end up, and the adapter basically just does a toString() on your data and sticks it in the view.

You can, of course, modify this behavior by overriding setViewText, which lets you reformat the text or modify the view as you wish; but it doesn’t give you the DB cursor, just a String, so you can’t pull the data yourself or refer to other columns. But not to despair (or turn to the NotSoSimpleCursorAdapter)! You can modify anything you want by providing a ViewBinder to the adapter.

The main reason I’m talking about this is because I think the documentation on this is just a little vague:

An easy adapter to map columns from a cursor to TextViews or ImageViews defined in an XML file. You can specify which columns you want, which views you want to display the columns, and the XML file that defines the appearance of these views. Binding occurs in two phases. First, if a SimpleCursorAdapter.ViewBinder is available, setViewValue(android.view.View, android.database.Cursor, int) is invoked. If the returned value is true, binding has occured. If the returned value is false and the view to bind is a TextView, setViewText(TextView, String) is invoked. If the returned value is false and the view to bind is an ImageView, setViewImage(ImageView, String) is invoked. If no appropriate binding can be found, an IllegalStateException is thrown.

OK, great. This also promises that you can put any kind of data in any kind of view (not just a TextView). But I didn’t know what it meant by “if a SimpleCursorAdapter.ViewBinder is available.” Turns out it’s pretty simple:

  1. Implement the SimpleCursorAdapter.ViewBinder interface (it has only one method, setViewValue, which gives you the Cursor and the view to work with – and just return false to let the adapter’s default behavior handle the binding). I did this for LogCursorAdapter in an inner class.
  2. Instantiate your implementation and use setViewBinder on your SimpleCursorAdapter instance to set it up as the binder. This makes it “available” for the process described above.

This is arguably better than overriding setViewText because you wouldn’t even have to subclass the adapter to do it – or even create a class (it could be an anonymous implementation). And of course you can access all of the cursor columns in any way you please. Nice.

As far as my earlier data retrieval woes, this gave me the ability to pull data out the way I wanted. Sqlite seems to be storing plenty of precision in the NUMERIC column type; it was just a matter of it being retrieved as a String that caused truncation of precision. In this case the solution was just to pull it out as a Long or Double as appropriate and format it myself (I also learned about DecimalFormat which was very helpful).

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