How to do a query with Cursor inside a thread? (android)

Question

I recently started my first app for college, and as part of my app I want to acces the contacts of the phone using this guide.

In the guide the onActivityResult looks like this:

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    // Check which request it is that we're responding to
    if (requestCode == PICK_CONTACT_REQUEST) {
        // Make sure the request was successful
        if (resultCode == RESULT_OK) {
            // Get the URI that points to the selected contact
            Uri contactUri = data.getData();
            // We only need the NUMBER column, because there will be only one row in the result
            String[] projection = {Phone.NUMBER};

            // Perform the query on the contact to get the NUMBER column
            // We don't need a selection or sort order (there's only one result for the given URI)
            // CAUTION: The query() method should be called from a separate thread to avoid blocking
            // your app's UI thread. (For simplicity of the sample, this code doesn't do that.)
            // Consider using CursorLoader to perform the query.
            Cursor cursor = getContentResolver()
                    .query(contactUri, projection, null, null, null);
            cursor.moveToFirst();

            // Retrieve the phone number from the NUMBER column
            int column = cursor.getColumnIndex(Phone.NUMBER);
            String number = cursor.getString(column);

            // Do something with the phone number...
        }
    }
}

It says i should use a thread or CursorLoader to do the query but so far I was unable to find a good solution for this. If I place the query method in a thread then I can't acces the data from it:

    Runnable r = new Runnable() {
                    @Override
                    public void run() {
                        Cursor cursor = getContentResolver()
                                .query(contactUri, projection, null, null, null);
                    }
                };
                Thread queryThread = new Thread(r);
                queryThread.start();
cursor.moveToFirst();
int column = cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER);

So in this code Android Studio cannot resolve the symbol "cursor" :( And so far I could not find a guide I understand on how to do this with CursorLoaders.

Answer 1

You can use an AsyncTask for the job!

     class WorkCursor extends AsyncTask<Cursor,Object,String> {

            String[] projection;
            Uri contactUri;

            public WorkCursor(String[] projection,Uri contactUri){
                this.contactUri = contactUri;
                this.projection = projection;
            }


            @Override
            protected String doInBackground(Cursor... cursors) {

                //This is done in the background

                Cursor cursor = MyActivity.this.getContentResolver()
                        .query(contactUri, projection, null, null, null);

                int column = cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER);
                String number = cursor.getString(column);

                return number;
            }

            @Override
            protected void onPostExecute(String number) {
                super.onPostExecute(number);

                //This is done on the UI thread
                functionCall(number);

            }
        }

        public void functionCall(String number){
            //This is the UI thread
            //You can do whatever you with your number
            Toast.makeText(this,"This is the number: "+number,Toast.LENGTH_SHORT).show();
        }

And then call the Asynctask like so:

new WorkCursor(projection,contactUri).execute();

One other way is to do like you did but do all the work inside the thread and then run the result on the UI thread like so:

new Thread(new Runnable() {
            @Override
            public void run() {
                Cursor cursor = getContentResolver()
                        .query(contactUri, projection, null, null, null);

                cursor.moveToFirst();
                int column = cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER);
                final String number = cursor.getString(column);
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        functionCall(number);
                    }
                });
            }
        }).run();

String number must be final in order to be accessible inside the other (runnable on UI) thread!

Disclaimer: Code is untested.