Question

I’m writing a custom ContentProvider that serves up content consisting of a single, constant string which I represent as a one-row table having columns _id = 0 and value = “SomeString”. This string is not stored in a database, so I developed a subclass of CrossProcessCursor that has does everything required to behave like what I described above.

The documentation for CrossProcessCursor is very sparse and doesn’t really explain what the fillWindow() method should be doing beyond the obvious. Based on the descriptions of CursorWindow’s methods, I put the following together, which I thought should cover it:

public class MyCursor implements CrossProcessCursor {
  ...
  public void fillWindow(int pos, CursorWindow window) {

        if (pos != 0) {  // There's only one row.
            return;
        }

        window.clear();
        window.allocRow();  // TODO: Error check, false = no memory
        window.setNumColumns(2);
        window.setStartPosition(0);
        window.putLong(0, 0, 0);
        window.putString("SomeString", 0, 1);
    }
}

As expected, it gets called with pos = 0 when a client application requests the content, but the client application throws an exception when it tries to go after the first (and only) row:

Caused by: java.lang.IllegalStateException: UNKNOWN type 48
     at android.database.CursorWindow.getLong_native(Native Method)
     at android.database.CursorWindow.getLong(CursorWindow.java:380)
     at android.database.AbstractWindowedCursor.getLong(AbstractWindowedCursor.java:108)
     at android.database.AbstractCursor.moveToPosition(AbstractCursor.java:194)
     at android.database.AbstractCursor.moveToFirst(AbstractCursor.java:248)
     at android.database.CursorWrapper.moveToFirst(CursorWrapper.java:86)
 ...(Snipped)...

Could anyone shed some light on what this method should be doing to return a correct-looking row to the client?

Thanks.

Answer 1

For what you’re doing you should check out the MatrixCursor. It uses the AbstractCursor#fillWindow implementation which calls toString on every object. Since you’re just sending a string anyway it should work fine for you.