Limit number of items in SimpleCursorAdapter when using custom content provider

Question

I'm trying to get used to using custom content providers. I've successfully managed to write a very simple application that on the press of a button adds a String to an sqlite database using a custom content provider. These database entries are then displayed in a ListView in the same activity.

I am trying to limit the number of items in the ListView to 5, but due to my lack in experience, I have no idea how to proceed.

This is what I'm using to fill the ListView

private void fillData() {

    String[] from = new String[]{commentsTable.COLUMN_COMMENT, commentsTable.COLUMN_ID};
    int[] to = new int[]{android.R.id.text1, android.R.id.text2};

    getLoaderManager().initLoader(0, null, this);
    adapter = new SimpleCursorAdapter(this, android.R.layout.two_line_list_item, null, from, to, 0);

    setListAdapter(adapter);
}

I followed this tutorial http://www.vogella.com/tutorials/AndroidSQLite/article.html#tutorial-sqlite-custom-contentprovider-and-loader to write an app similar to the app in the tutorial.

I have tried using a Cursor instead of null but I'm getting a java.lang.NullPointerException error because of the method .getWritableDatabase().

score 1 · Accepted Answer · edited May 23 '17 at 12:22

After some research, I have managed to solve this and thought I would post an answer for anyone who stumbles across this question.

In my customContentProvider class I added the variables:

public static final String QUERY_PARAMETER_LIMIT = "limit";
public static final String QUERY_PARAMETER_OFFSET = "offset";

and then edited the query method to include:

public Cursor query(Uri uri, ...) {
    String limit = uri.getQueryParameter(QUERY_PARAMETER_LIMIT);
    String offset = uri.getQueryParameter(QUERY_PARAMETER_OFFSET);

    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();

    // ...

    Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, sortOrder, limitString);

    //...

    return c;
}

Then when getting a cursor simply use the Uri

Uri CONTENT_URI = customContentProvider.CONTENT_URI.buildUpon()
            .appendQueryParameter(customContentProvider.QUERY_PARAMETER_LIMIT,
                    String.valueOf(limit))
            .appendQueryParameter(customContentProvider.QUERY_PARAMETER_OFFSET,
                    String.valueOf(offset))
            .build();

Reference:

https://stackoverflow.com/a/24055457/6735035

Vladislav Sazanovich · Answer 2 · 2016-08-19T15:18:29.517

0

CursorAdapter has method getCount(). You could implement it in your class like this.

public int getCount() {
    int superCount = super.getCount();
    return Math.min(superCount, 5);
}

So you need to inherit SimpleCursorAdapter and redefine method getCursor().

Crate this class

public class CustomCursorAdapter extends SimpleCursorAdapter {

    public CustomCursorAdapter(Context context, int layout, Cursor c, String[] from, int[] to, int flags) {
        super(context, layout, c, from, to, flags);
    }

    @Override
    public int getCount() {
        int superCount = super.getCount();
        return Math.min(superCount, 5);
    }
}

And in your code change SimpleCursorAdapter to CustomCursorAdapter

private void fillData() {

    String[] from = new String[]{commentsTable.COLUMN_COMMENT, commentsTable.COLUMN_ID};
    int[] to = new int[]{android.R.id.text1, android.R.id.text2};

    getLoaderManager().initLoader(0, null, this);
    adapter = new CustomCursorAdapter(this, android.R.layout.two_line_list_item, null, from, to, 0);

    setListAdapter(adapter);
}

edited Aug 19 '16 at 15:18

answered Aug 19 '16 at 13:36

Vladislav Sazanovich

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Which class should I add apply these too? My custom content provider? – somethingRandom Aug 19 '16 at 14:17
@somethingRandom I've added some expanations. Hope this helps. – Vladislav Sazanovich Aug 19 '16 at 14:28
Doesn't seem to work, the app is crashing. I was getting the error "java.lang.IllegalStateException: this should only be called when the cursor is valid" when I ran the app on the previous code. So I uninstalled the app and built it again but now I'm getting the error "java.lang.IllegalStateException: couldn't move cursor to position 0". – somethingRandom Aug 19 '16 at 15:02
@somethingRandom It's actually bug in my code. Change Math.max to Math.min )) – Vladislav Sazanovich Aug 19 '16 at 15:18
It works! Although, is it possible to simply "feed" the SimpleCursorAdapter 5 items instead of having to create an entire class? – somethingRandom Aug 19 '16 at 15:36
Actually it says adapter to have max 5 items. As I know it the simplest way to achieve this. – Vladislav Sazanovich Aug 19 '16 at 15:38
Also you could make CustomCursorAdapter to be inner class to not mess your project files. – Vladislav Sazanovich Aug 19 '16 at 15:42

Limit number of items in SimpleCursorAdapter when using custom content provider

2 Answers2