I am trying to show two consecutive images in an Android app, which are received through a socket (from a C program using sendfile). The sender code seems to work ok, and I am having issues with the Android code side.
Part of the code in the Android app is the following:
public class DisplayNewActivity extends Activity {
...
#Override
public void onCreate(Bundle savedInstanceState) {
....
mHandler = new Handler() {
#Override
public void handleMessage(Message msg) {
Drawable d2;
d2 = (Drawable)msg.obj;
imageSock.setImageDrawable(d2); // to set the arrived image in the imageshow object
}
};
...
cThread = new Thread(new ClientThread());
rThread = new Thread(new RcvThread());
cThread.start();
}
public class ClientThread implements Runnable {
public void run() {
// thread used for socket connection.
...
rThread.start(); // once the connection has been established
...
}
}
#SuppressLint("HandlerLeak")
public class RcvThread implements Runnable {
public void run() {
while (connected) {
try {
InputStream inputStream = socket.getInputStream();
Drawable d = Drawable.createFromStream(inputStream, null);
Message msg = new Message();
msg.obj = d;
mHandler.sendMessage(msg);
} catch (Exception e) {
Log.e("SocketConnectionv02Activity", "C: ErrorRCVD", e);
}
}
}
}
}
The problem I am facing is that after the first image received by the Android app is shown correctly, then the next one received (which is correctly received) is not shown and leaves the imageview object showing a white space.
Any suggestion/idea to solve this issue?.
Thanks in advance for any help you could provide.
EDIT:
public class DisplayNewActivity extends Activity {
...
#Override
public void onCreate(Bundle savedInstanceState) {
....
mHandler = new Handler() {
#Override
public void handleMessage(Message msg) {
Bitmap d2;
d2 = (Bitmap)msg.obj;
imageSock.setImageBitmap(d2); // to set the arrived image in the imageshow object
}
};
...
cThread = new Thread(new ClientThread());
rThread = new Thread(new RcvThread());
cThread.start();
}
public class ClientThread implements Runnable {
public void run() {
// thread used for socket connection.
...
rThread.start(); // once the connection has been established
...
}
}
#SuppressLint("HandlerLeak")
public class RcvThread implements Runnable {
public void run() {
while (connected) {
try {
DataInputStream in = new DataInputStream(socket.getInputStream());
Bitmap d = BitmapFactory.decodeStream(in);
Message msg = new Message();
msg.obj = d;
mHandler.sendMessage(msg);
} catch (Exception e) {
Log.e("SocketConnectionv02Activity", "C: ErrorRCVD", e);
}
}
}
}
}
It sounds like the issue you are having is in decoding the data into a proper image after receiving it.
I might recommend not using Drawable.createFromStream() and instead using BitmapFactory.decodeStream() or manually downloading the data into a byte[] first and using BitmapFactory.decodeByteArray(). Sometimes the latter is useful if the former can't sufficiently keep up with the decoder as the data is received.
The method you are currently using actually ends up calling BitmapFactory.descodeResourceStream(), which is used to read image data out of the local res/ package and not so much from a remote socket.
Related
I am a beginner in Android app dev. Recently I am trying to make a face detection app using FaceDetector.
In the code below is my main activity class. I have a Runnable to loop through a set of images, convert to bitmaps and send them to FaceOverlayView to find and draw faces. The loop can go through all 4 items.
However, as I tried to make it loop all over again by setting index to 0 after the last item, the app crashes. I observed the behavior that the app will crash trying to reload an image loaded before. Would you please give me any insight on this? Many thanks in advance.
public class MainActivity extends AppCompatActivity {
private FaceOverlayView mFaceOverlayView;
Handler handler;
Thread thread;
ArrayList<Integer> imgID = new ArrayList<Integer>(Arrays.asList(R.raw.face1, R.raw.face2, R.raw.face3, R.raw.face4));
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mFaceOverlayView = (FaceOverlayView) findViewById(R.id.face_overlay);
thread = new Thread(new myThread());
thread.start();
handler = new Handler() {
#Override
public void handleMessage(Message msg) {
if (msg.arg1 == -1) {
//thread.interrupt();
}
Bitmap bitmap = (Bitmap) msg.obj;
mFaceOverlayView.setBitmap(bitmap);
}
};
}
class myThread implements Runnable {
#Override
public void run() {
int index = 0;
while (index < imgID.size()) {
InputStream stream = getResources().openRawResource(imgID.get(index));
Bitmap bitmap = BitmapFactory.decodeStream(stream);
Message msg = Message.obtain();
msg.obj = bitmap;
handler.sendMessage(msg);
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
index++;
if (index >= imgID.size()) {
index = 0;
}
bitmap.recycle();
bitmap = null;
}
}
}
}
I made two classes, the first is Server class that runs a thread to wait for and accept a socket connection from the client.
the second class is the EchoThread class that starts a new thread that gets the text message passed by the socket connection. the reason for this is becase it is requied to do this so I can connect more than one client at a time to the server. so I created this class. It is called in the while(true) loop in the Server class to start a new thread when a connection is made.
the problem is that the logcat for this app is a nullPointer exception for the EchoThread class, at this line:
handler.post(new Runnable() {
why am I getting this error message and what to do about it?
Server class:
public class ServerThread implements Runnable {
public void run() {
try {
if (SERVERIP != null) {
handler.post(new Runnable() {
#Override
public void run() {
serverStatus = "Listening on IP: " + SERVERIP;
}
});
serverSocket = new ServerSocket(SERVERPORT);
while (true) {
// listen for incoming clients
Socket client = serverSocket.accept();
handler.post(new Runnable() {
#Override
public void run() {
Intent intent = new Intent();
intent.setAction("com.example.diceRolled");
intent.putExtra("serverStatus","Connected");
sendBroadcast(intent);
}
});
new EchoThread(Server.this, client).start();
} // end while(true) method
} else { // the rest of the code for Server class....
EchoThread class:
public class EchoThread extends Thread {
protected Socket socket;
private String line;
private Handler handler;
private Context context;
private Socket client;
public EchoThread(Context c, Socket clientSocket) {
this.socket = clientSocket;
this.context = c;
}
public void run(){
try {
BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
while ((line = in.readLine()) != null) {
// Log.d("ServerActivity", line);
handler.post(new Runnable() {
private String receivedCommand;
#Override
public void run() {
receivedCommand = line;
Intent intent = new Intent();
intent.setAction("com.example.diceRolled");
intent.putExtra("serverStatus", line.trim());
context.sendBroadcast(intent);
Toast.makeText(context, "sent message " + receivedCommand, Toast.LENGTH_SHORT).show();
// the rest of the code for EchoThread class....
Your handler stays null, since you make it as a class variable
private Handler handler;
but then you never actually give it anything to hold.
When you come across
handler.post()
An NPE is thrown.
Therefore, you must instantiate handler, or give it a non-null reference to hold.
If you want more info about Handlers and Loopers, this and this may be of value (same links as this SO answer.
Using socket connection i need to have two threads, one for reading and one for writing. I found other questions about socket connections but I don't understand how i can use the same socket in two different threads.
I have to create a socket in a different thread from the UI thread, so i need to start a thread to create the socket. Where can i start the two threads?
Sample code structure to give you an idea.
public class SocketActivity extends Activity {
Socket s;
OutputStream dout;
String ip = "127.0.0.1";
int port = 8080;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
new Thread(new Runnable() {
#Override
public void run() {
try {
s = new Socket(ip, port);
new Thread(new ReaderRunnable(s));
new Thread(new WriteRunnable(s));
} catch (IOException e) {
e.printStackTrace();
//Handle error state
}
}
});
}
// You can put this class outside activity with public scope
class ReaderRunnable implements Runnable {
Socket socket;
public ReaderRunnable(Socket socket) {
this.socket = socket;
}
#Override
public void run() {
if (socket != null && socket.isConnected()) {
try {
OutputStream out = new BufferedOutputStream(socket.getOutputStream());
//Do reader code
} catch (IOException e) {
e.printStackTrace();
}
} else {
//Handle error case
}
}
}
// You can put this class outside activity with public scope
class WriteRunnable implements Runnable {
Socket socket;
public WriteRunnable(Socket socket) {
this.socket = socket;
}
#Override
public void run() {
if (socket != null && socket.isConnected()) {
try {
InputStream out = new BufferedInputStream(socket.getInputStream());
//Do writer code
} catch (IOException e) {
e.printStackTrace();
}
} else {
//Handle error case
}
}
}
}
Judging by your question this is client side. You don't have to use the socket itself in two different threads. For the read thread you use the InputStream of the socket, and for the write thread you use the OutputStream.
That way you don't have to create a seperate thread just for the socket. Both the read and write threads can be started from the UI thread. For creating the threads i refer you to the Android Documentation Processes and Threads.
I am trying to load an object from a server in Android. This object is loaded in a thread. When loading is finished, an _objectHandler is called to get some key - values from the object, for example, the _filename key. Every time a filename is retrieved, I want to display it. For this reason, I am looping over the element of the loaded object in a second thread, and calling a _handler every time a value is loaded. What I want to get is all the _filename values, but what I am getting is only the last value of the _fielName. what I am doing wrong?
ArrayList <myObject> object;
String filename;
Thread thread = new Thread (MyActivity.this);
thread.start();
public void run() {
Looper.prepare();
try {
object = getObjectFromServer();
} catch (Exception e) {
e.printStackTrace();
}
_objectHandler.sendEmptyMessage(0);
Looper.loop();
}
Handler _objectHandler = new Handler() {
#Override
public void handleMessage(Message msg) {
for (int i = 0; i < object.size(); i++) {
myObject obj= object(i);
new Thread(new Runnable() {
public void run() {
filename= obj.getFileName();
Message msg = new Message();
_handler.sendEmptyMessage(0);
}
}).start();
}
}
};
Handler _handler = new Handler() {
#Override
public void handleMessage(Message msg) {
Log.i("The fielname is ", " filename" + filename
}
};
you can use android.os.Handler class. This will provide you a mechanism for enqueue an action to be performed on a different thread than your own.
I'm developing an Android application.
This application will have a server to start a DatagramSocket as a server. It will wait for incoming message. When the socket get a message I will process it.
To start a UDP Server socket I'm going to use a Local Service. This service will have a worker thread where I'm going to listen to incoming messages.
This is my unfinished Local Service implementation:
public class UDPSocketBackgroundService extends Service
{
private static final String TAG = "UDPSocketBackgroundService";
private ThreadGroup myThreads = new ThreadGroup("UDPSocketServiceWorker");
private Handler mServiceHandler;
#Override
public void onCreate()
{
super.onCreate();
Log.v(TAG, "in onCreate()");
}
#Override
public IBinder onBind(Intent arg0)
{
try
{
new Thread(myThreads, new UDPServerThread("X", 8888)).start();
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
}
And this is my also unfinished Worker Thread implementation:
public class UDPServerThread extends Thread
{
private static final int MESSAGE_SIZE = 256;
protected DatagramSocket socket = null;
protected boolean end = false;
public UDPServerThread(String serverName, int port) throws IOException
{
super(serverName);
socket = new DatagramSocket(port);
}
public void run()
{
while (!end)
{
try
{
byte[] buf = new byte[MESSAGE_SIZE];
// Wait an incoming message.
DatagramPacket packet = new DatagramPacket(buf, buf.length);
socket.receive(packet);
// TODO: Notify Service with packet received
}
catch (IOException e)
{
// TODO Mensaje de error.
e.printStackTrace();
}
}
}
}
Those classes have their own file (they are on different files).
Here:
socket.receive(packet);
//TODO: Notify Service with packet received
How can I notify service that we have received a packet? I want to send to service that packet also.
Here there is an example on how to communicate from Main thread to worker thread. But, I don't need that, I'm looking for an example on how to communicate from worker thread to service.
I've found this example, but I don't understand it very well because on that example both classes are declare it on the same file.
As you can see, I'm a newbie on Android development.
If you know a better approach, please tell me.
When you create the UDPServerThread, you could pass in a reference to the UDPSocketBackgroundService and then call a method on it (processPacket() for example) when packets are received. This processPacket() method will need to use some sort of synchronization.
Here's a small code excerpt of the related functions:
public class UDPSocketBackgroundService extends Service
{
....
#Override
public IBinder onBind(Intent arg0)
{
try
{
new Thread(myThreads, new UDPServerThread(this, "X", 8888)).start();
// Notice we're passing in a ref to this ^^^
}
...
}
public void processPacket(DatagramPacket packet)
{
// Do what you need to do here, with proper synchronization
}
}
public class UDPServerThread extends Thread
{
private static final int MESSAGE_SIZE = 256;
protected DatagramSocket socket = null;
protected boolean end = false;
protected UDPSocketBackgroundService = null;
public UDPServerThread(UDPSocketBackgroundService service, String serverName, int port) throws IOException
{
super(serverName);
this.service = service;
socket = new DatagramSocket(port);
}
...
public void run()
{
while (!end)
{
try
{
byte[] buf = new byte[MESSAGE_SIZE];
// Wait an incoming message.
DatagramPacket packet = new DatagramPacket(buf, buf.length);
socket.receive(packet);
service.processPacket(packet);
}
...
}
...
}
}
Notice that going this approach, the UDPSocketBackgroundService is now "tightly coupled" with the UDPServerThread. Once you get this working, you may consider refactoring it with a more elegant design where there is less coupling, but for now this should get you going :)