Develop Reference

Listview not loading images till I scroll the screen

I am using an async call inside my Custom Adapter class to load images in a Listview. However, the images are not shown till I scroll up/down atleast slightly. Please let me know what might be the reason. Thanks for your help.
private class LoadImage extends AsyncTask<Void, Void, Void>
{
private String fileName = null;
private ImageView imgViewToLoad = null;
LoadImage(String fileName, ImageView imgViewToLoad)
{
this.fileName = fileName;
this.imgViewToLoad = imgViewToLoad;
}
#Override
protected Void doInBackground(Void... args)
{
return null;
}
//This is executed on main UI thread
#Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
Utils.mImageFetcher.loadImage(fileName, imgViewToLoad);
}
}
This is in my getView()
----------------------
ViewHolderIncomingImg holderInImg = null;
if (null != convertView &&
(convertView.getTag() instanceof ViewHolderIncomingImg && !isFirstMsg))
{
holderInImg = (ViewHolderIncomingImg) convertView.getTag();
if (!multiSelectionMode)
{
if (!mSelectedItemsIds.get(position) && convertView.isActivated())
convertView.setActivated(false);
}
}
else
{
convertView = mInflater.inflate(R.layout.conv_list_item_incoming_img, parent, false);
holderInImg = new ViewHolderIncomingImg();
..............
new LoadImage(convRowItems.get(position).getMessage(), holderInImg.image).execute();

As Listview use the concept of recycling its view. The images are not showing when the async call finish.
So go for listview lazy loading approach it will help you.

Receiving image in Asynctask and display it in ImageView

I'm trying receive the image over TCP (in Asynctask) and display it in ImageView but I have an error in onPostExecute. Anyone know why?
And also whether idea of receiving is correct, if the next step will be recurring receiving image over TCP and displaying it?
Code:
public class TcpClient extends Activity {
ImageView imageView;
public static String aHost;
public String aSocketIn;
public static int aSocketInInt;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.bundle_result);
imageView = (ImageView) findViewById(R.id.imageView);
Intent intent = getIntent();
aHost = intent.getStringExtra("addressIp");
aSocketIn = intent.getStringExtra("socketIn");
aSocketInInt = Integer.parseInt(aSocketIn);
new DownloadImageTask(aHost,aSocketInInt).execute();
} }
public class DownloadImageTask extends AsyncTask <Void,Void,Bitmap > {
public Bitmap bitmap = null;
String Host;
int SocketIn;
public DownloadImageTask(String Host,int SocketIn) {
this.Host = Host;
this.SocketIn = SocketIn;
}
#Override
protected Bitmap doInBackground(Void... params) {
ClientIn clientIn;
try {
InetAddress serwerAddress = InetAddress.getByName(Host);
Socket socket = new Socket(serwerAddress, SocketIn);
clientIn = new ClientIn(socket);
bitmap = clientIn.Receive();
return bitmap;
}
catch (Exception e) {
e.printStackTrace();
return null;
}
}
#Override
protected void onPostExecute(Bitmap result) {
imageView.setImageBitmap(result); // ERROR: Cannot resolve symbol 'imageView'
} }

Looks like DownloadImageTask class is not inner-class of TcpClient class which is extending Activity,so to access imageView object of ImageView in other class, need to send it on DownloadImageTask using class constructor in same way as doing currently for getting Host and SocketIn in DownloadImageTask class.
Change DownloadImageTask as for to using imageView "
public DownloadImageTask(String Host,int SocketIn,ImageView imageView) {
this.Host = Host;
this.SocketIn = SocketIn;
this.imageView=imageView;
}

Downloading and setting a wallpaper

I have this little piece of code and I want to achieve this: program should set a wallpaper from linked image.
ImgDownload:
public class ImgDownload extends AsyncTask {
private String requestUrl;
private ImageView view;
private Bitmap pic;
private ImgDownload(String requestUrl, ImageView view) {
this.requestUrl = requestUrl;
this.view = view;
}
#Override
protected Object doInBackground(Object... objects) {
try {
URL url = new URL(requestUrl);
URLConnection conn = url.openConnection();
pic = BitmapFactory.decodeStream(conn.getInputStream());
} catch (Exception ex) {
}
return null;
}
#Override
protected void onPostExecute(Object o) {
view.setImageBitmap(pic);
}
}
main
public class MainActivity extends Activity {
private ImageView img;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
img= (ImageView)findViewById(R.id.img);
//!!!! This is where I am stuck :)
Object s = new ImgDownload("http://images1.wikia.nocookie.net/__cb20120402213849/masseffect/images/4/42/Uncharted_Worlds_Codex_Image.jpg",img );
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
How to instantiate/create this class in my mainActivity, so it could download img from link? Any help suggestions, thoughts, will be appreciated :)

You execute this AsyncTask like this:
ImgDownload downloader = new ImgDownload("http://images1.wikia.nocookie.net/__cb20120402213849/masseffect/images/4/42/Uncharted_Worlds_Codex_Image.jpg",img);
downloader.execute();
But I would not recommend using your code as it will produce memory leaks. For example try to rotate your device while it is downloading an image. I guarantee you your application will crash. Plus AsyncTask is a generic class. You could use that to make your code a little simpler. Here is my improved image download task:
public class ImgDownload extends AsyncTask<Void, Void, Bitmap> { // Use Generics
private final String requestUrl;
private final WeakReference<ImageView> imageViewReference; // Use WeakReference to prevent memory leaks
public ImgDownload(String requestUrl, ImageView view) {
this.requestUrl = requestUrl;
this.imageViewReference = new WeakReference<ImageView>(view);
}
#Override
protected Bitmap doInBackground(Void... objects) {
try {
URL url = new URL(requestUrl);
URLConnection conn = url.openConnection();
return BitmapFactory.decodeStream(conn.getInputStream()); // Return bitmap instead of using global variable
} catch (Exception ex) {
}
return null;
}
#Override
protected void onPostExecute(Bitmap bitmap) {
ImageView imageView = imageViewReference.get();
if(imageView != null && bitmap != null) { // Check if image or ImageView are null
imageView.setImageBitmap(bitmap);
}
}
}

new ImgDownload("http://images1.wikia.nocookie.net/__cb20120402213849/masseffect/images/4/42/Uncharted_Worlds_Codex_Image.jpg", MainActivity.img).execute();

Undesired delay at beginning an Acitivity

I am working with some Acitivitys , it's working pretty well. But i am having a strange delay on it.
And I figure it out that, it was about this part of the code, where I am loading stored image in the SDCard.
if(p.getAdress() != null){
Bitmap bitmap = BitmapFactory.decodeFile(p.getAdress());
new_image.setBackgroundDrawable(null);
new_image.setImageBitmap(bitmap);
}
Why this simple code is taking too long to execute?
How to solve it?
If I take this code off, everything works as i wished.

You shouldn't load large bitmaps directly on the UI thread.
Actually, the best reference to loading large Bitmaps efficiently can be found here.
And right here you can find good information on how you can load them using an AsyncTask.
This is the method they show you there (you can even download the sample!)
class BitmapWorkerTask extends AsyncTask<Integer, Void, Bitmap> {
private final WeakReference<ImageView> imageViewReference;
private int data = 0;
public BitmapWorkerTask(ImageView imageView) {
// Use a WeakReference to ensure the ImageView can be garbage collected
imageViewReference = new WeakReference<ImageView>(imageView);
}
// Decode image in background.
#Override
protected Bitmap doInBackground(Integer... params) {
data = params[0];
return decodeSampledBitmapFromResource(getResources(), data, 100, 100));
}
// Once complete, see if ImageView is still around and set bitmap.
#Override
protected void onPostExecute(Bitmap bitmap) {
if (imageViewReference != null && bitmap != null) {
final ImageView imageView = imageViewReference.get();
if (imageView != null) {
imageView.setImageBitmap(bitmap);
}
}
}
}
public void loadBitmap(int resId, ImageView imageView) {
if (cancelPotentialWork(resId, imageView)) {
final BitmapWorkerTask task = new BitmapWorkerTask(imageView);
final AsyncDrawable asyncDrawable =
new AsyncDrawable(getResources(), mPlaceHolderBitmap, task);
imageView.setImageDrawable(asyncDrawable);
task.execute(resId);
}
}

Your can try this way. It help you
private class LongOperation extends AsyncTask<String, Void, String> {
#Override
protected String doInBackground(String... params) {
if(p.getAdress() != null){
Bitmap bitmap = BitmapFactory.decodeFile(p.getAdress());
new_image.setBackgroundDrawable(null);
new_image.setImageBitmap(bitmap);
}
return "Executed";
}
#Override
protected void onPostExecute(String result) {
}
#Override
protected void onPreExecute() {
}
#Override
protected void onProgressUpdate(Void... values) {
}
}

Android: alert dialog in a class without activity

i have this class:
public class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {
ImageFromWeb ifw;
private String url;
private final WeakReference<ImageView> imageViewReference;
public DownloadImageTask(ImageView imageView) {
imageViewReference = new WeakReference<ImageView>(imageView);
}
#Override
protected Bitmap doInBackground(String... params) {
url = params[0];
try {
return BitmapFactory.decodeStream(new URL(url).openConnection().getInputStream());
} catch (MalformedURLException e) {
e.printStackTrace();
return null;
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
#Override
protected void onPostExecute(Bitmap result) {
if (isCancelled()) {
result = null;
}
if (imageViewReference != null) {
ImageView imageView = imageViewReference.get();
if (imageView != null) {
imageView.setImageBitmap(result);
}
}
}
#Override
protected void onPreExecute() {
if (imageViewReference != null) {
ImageView imageView = imageViewReference.get();
if (imageView != null) {
---------> imageView.setImageResource(R.drawable.pw);
}
}
}
}
and the main activity:
public class ImageFromWeb extends Activity {
private String path = "http://....";
private ImageView imageView;
public void onCreate(Bundle bundle) {
super.onCreate(bundle);
setContentView(R.layout.main);
ImageView mChart = (ImageView) findViewById(R.id.imview);
mChart.setTag(path);
new DownloadImageTask(mChart).execute(path);
}
}
I want to put in the point of arrow(in DownloadImageTask class) an alert dialog! How can i do this? Because this class isn't an activity.
thanks :)

change the constructor and pass a Context object
Context mContext;
public DownloadImageTask(ImageView imageView,Context mContext) {
imageViewReference = new WeakReference<ImageView>(imageView);
this.mContext = mContext;
}
Now you can use this Context to create dialogs
You can even cast mContext to your Activity class and call functions within your Activity

Move the Async Task to your activity and use that to call your DownloadImageTask class & methods. This will make your life a lot easier.

pass a Activity instance to the class where you want to display dialog, and check
if(!actvity.isFinishing){
//show dialog
}

You can have a static Context in your Application like this:
public static Context CurrentContext;
and a custom abstract Activity that sets currentContext upon creation like this:
public abstract class CustomActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
MyApplication.CurrentContext = this;
}
}
Then you would get context like this:
AlertDialog.Builder dlgBuilder = new AlertDialog.Builder(MyApplication.CurrentContext);
dlgBuilder.setTitle("Context Example");
dlgBuilder.setMessage("I am being shown from the application Static context!");
dlgBuilder.setNeutralButton("Ok", null);
dlgBuilder.show();
This way you never have to worry about context wether you are in a background task or directly in an Activity it will work for most cases.
hope this helps!