Load image from URL, AsyncTask

Actually, the loading images from URL to ImageView (ImageView itself is in GridView or ListView) is not a simple task. You should provide memory and disk caching to avoid reload image again and again.

The simplest way is use library:

1. Picasso (picasso-2.3.4.jar)
2. Android universal image loader (grown from LazyList)
3. Volley
4. Glide
5. Query

There is a comparison of these libraries (pdf 1, 2). Also this.

Also good article by Google’s ingineer (pdf)

---

How to use Picasso in Android Studio:
you should edit your build.gradle file by adding

compile 'com.squareup.picasso:picasso:2.3.4'

My file looks like below

apply plugin: 'com.android.application'

android {
    compileSdkVersion 19
    buildToolsVersion "20.0.0"

    defaultConfig {
        applicationId "com.arvifox.testpica"
        minSdkVersion 16
        targetSdkVersion 19
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            runProguard false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    compile 'com.squareup.picasso:picasso:2.3.4'
}

How to save image on disk by Picasso:

public class MainActivity extends Activity{
    ImageView imageView;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);        
        imageView = (ImageView) findViewById(R.id.image);
        Picasso.with(this).load("your_url").error(R.drawable.error_detail)
        .placeholder(R.drawable.ic_launcher)
        .into(imageView, new EmptyCallback() {
            @Override public void onSuccess() {
                //to-do
            }            
            @Override
            public void onError() {
                //to-do
            }            
        });
        Picasso.with(this).load("your_url")
        .into(target);
    }
 
    private Target target = new Target() {
        @Override
        public void onBitmapLoaded(final Bitmap bitmap, Picasso.LoadedFrom from) {
            new Thread(new Runnable() {
                @Override
                public void run() {               
                    File file = new File(Environment.getExternalStorageDirectory().getPath() +"/path.jpg");
                    try 
                    {
                        file.createNewFile();
                        FileOutputStream ostream = new FileOutputStream(file);
                        bitmap.compress(CompressFormat.JPEG, 75, ostream);
                        ostream.close();
                    } 
                    catch (Exception e) 
                    {
                        e.printStackTrace();
                    }
                }
            }).start();
        }
    };
}

In the first part of code I put image to ImageView by just a few lines of code.

In second part I save image on disk by Target class that is described in Picasso library.

Note: Picasso uses the http headers to cache the image so it may not be stored for long. After sometime, it tries to load the image again from server instead of the cache. As a workaround, use “OkHttp” library made by the same people as Picasso. Just download its jar from here and put into your project’s libs directory. Picasso will use it by default and cache will be stored longer.