How to use Cursor Loader? Example

Why we need it?

Answer is simple, because it is a background thread. Cursor Loader doesn’t block UI thread like the it’s old way; Activity.managerQuery.

Where we use it?

            It is effective tool when we have a large number of items in SQlite tables.

How we use?

            Setup;

We need a content provider to use Cursor Loader. Let’s write simple method for query database. Assume that database has some android phone. And in order to make it slow for take advange of Cursor Loader it will sleep 5 seconds in query.

LazyContentProvider.java

    public static CursorLoader getCursorLoader(Context paramContext) {

        Log.i(TAG,"try to block query");

        Thread.sleep(5000); //miliseconds

        String[] a = { Boolean.toString(false) };

        return new CursorLoader(paramContext, Your.URI, ColumnNamesYouWantToQuery, null, null, "_id ASC ");

    }

            This simple query return a cursor with list of element.

String[]{"Samsung Galaxy S6","HTC One M9","Sony Xperia Z5","LG G4", "Nexus 5X", "Nexus 6P"}

Other than this database can be filled from WEB or just pulling from existing content provider.

            Usage;

Let’s create a class with CursorLoader implementation.

CursorLoaderActivity.java

package com.kozaxinan.sekreter;

import android.app.ListActivity;

import android.app.LoaderManager;

import android.content.CursorLoader;

import android.content.Intent;

import android.content.Loader;

import android.database.Cursor;

import android.os.Bundle;

import android.util.Log;

import android.view.View;

import android.widget.ListView;

public class  CursorLoaderActivity extends ListActivity implements LoaderManager.LoaderCallbacks<Cursor> {

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);    

    }

    @Override

    protected void onResume() {               

// if you want to restart loader

        getLoaderManager().restartLoader(0, null, this);

        super.onResume();

    }

    @Override

    public Loader<Cursor> onCreateLoader(int arg0, Bundle arg1) {

       //this is where we create background thread for cursor

        CursorLoader localCursorLoader = getCursorLoader(this);

        return localCursorLoader;

    }

    @Override

    public void onLoadFinished(Loader<Cursor> arg0, Cursor localCursor) {

        //make something with cursor and close it

        localCursor.close();

    }

    @Override                 

    public void onLoaderReset(Loader<Cursor> arg0) {

    }

}

It is new API!!!

            CursorLoader is available before API level 11. But Android team add this good feature in the Compatibility Library Package.

            This API works in Fragment with Compatibility Library. Therefor we need a init method to call CursorLoader;

        getSupportLoaderManager().initLoader(LOADER_ID, null, this);

For this method we need a loader_id which we can select randomly.

This is a basic way to use CursorLoader. Use this API in your project to avoid blocked UI.