从不同的AsyncTask更改AsyncTask中的布局

Question

I want to do the following. I want to display a list with information and images. These images take a while to load, so I thought I would do it differently. I would use two AsyncTasks. The first creates all the layouts and fills it with data except the images. The second one just inserts the images into the layout. The problem I'm encountering is, that I don't know how this would be possible?

In my first AsyncTask, I'm creating TableLayouts and rows and then fill them with data

This is just a bit of my code to understand it a bit how I create the layout

Here I create firstly the TableLayouts and TableRows

tableLayout [i] = new TableLayout   (getActivity());
headingRow  [i] = new TableRow      (getActivity());
headlineRow [i] = new TableRow      (getActivity());
imageDescRow[i] = new TableRow      (getActivity());
spaceView   [i] = new LinearLayout  (getActivity());

Then I fill TextViews with data

headline    [i].setText( headlineArr    [i] );
date        [i].setText( realDate           );
source      [i].setText( sourceArr      [i] );
description [i].setText( descriptionArr [i] );

Then I add the TextViews to the Tables and the Tables to the Layout. The code is of course much bigger and does way more than what I'm just doing. And it works without any problems. The only problem still encountering is that Image Loading takes too long to load and I don't want to stop the User from using my app just because Images are loading.

What would be the best way to do that? I thought I would just create another AsyncTask in the onPostExecute method from the current asynctask and pass the URLs of the Images as a parameter. And then in the doInBackgroundMethod I would add the images. But how do I use a layout from another AsyncTask in the new AsyncTask? And wouldn't it destroy the whole layout if I would leave the images empty?

What would be the best way to do such a lazy load?

Answer 1

I don't see any problem here. AsyncTask 's onPosExecute method runs on UIThread and you can reach any ui component there. To summarize, your flow must be sth like this:

1. Load data with an AsyncTask let me name it NoImageAsyncTask . This task will do long operation on its doInBackground method which runs on a seperate thread than UIThread .

2. When NoImageAsyncTask finished, its onPosExecute method will be invoked. Since onPostExecute method runs on UIThread , you can now update your UI wit this data.

3. At onPostExecute method, start n(n is the count of imageUrls you have from the data you got) new AsyncTasks (let me name it ImageAsyncTask ). These ImageAsyncTasks ' should download images on their doInBackground method. After download completed onPostExecute will be triggered and you get the image now. You can update your UI on onPostExecute method because it runs on UIThread .

BTW I recommend you to use a library for image loading purpose. I'm currently using Shutterbug for this.