Develop Reference

Why this Android Socket program don't work?

I have connected my Android device to the wifi shared by my laptop. After I input the IP address and click "OK" in the Android app, I can not find any packets to/from the address in Wireshark (packet sniffer)
I have added this to the manifest of the Android Project:
<uses-permission android:name="android.permission.INTERNET"/>
Android Code:
private boolean attemptOpenDoor(){
// Store values at the time of the login attempt.
String studentId = mStudentIdView.getText().toString();
String password = mPasswordView.getText().toString();
final EditText et = new EditText(this);
new AlertDialog.Builder(this).setTitle("please input IP address")
.setIcon(android.R.drawable.ic_dialog_info).setView(et)
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface arg0, int arg1) {
IPAddr = et.getText().toString();
}
}).setNegativeButton("cancel", null).show();
try {
Socket socket = new Socket();
socket.connect(new InetSocketAddress(IPAddr, 8866), 5000);
OutputStream ou = socket.getOutputStream();
ou.write((studentId+password).getBytes("UTF-8"));
ou.close();
socket.close();
}catch (SocketTimeoutException aa) {
//连接超时 在UI界面显示消息
AlertDialog alertDialog = new AlertDialog.Builder(LoginActivity.this).create();
alertDialog.setMessage("服务器连接失败！请检查网络是否打开");
alertDialog.setButton(DialogInterface.BUTTON_POSITIVE, "确定", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
}
});
alertDialog.show();
} catch (Exception e) {
e.printStackTrace();
}
return true;
}

The program doesn't work because at the time that you're trying to open the socket using:
socket.connect(new InetSocketAddress(IPAddr, 8866), 5000);
the dialog is still up and value of IPAddr has not yet been set. Make sure that you only start connecting once the user has entered a valid input in the field.
Also, beware that the method above will block whichever thread it's running on until a connection is established or 5 seconds go by, meaning that it'd be unwise to call it directly inside of the OnClickListener. You should probably use an AsyncTask or similar to avoid blocking the UI thread while the connection is taking place.

You should move your connect codes after "onClick".
new AlertDialog.Builder(this).setTitle("please input IP address")
.setIcon(android.R.drawable.ic_dialog_info).setView(et)
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface arg0, int arg1) {
IPAddr = et.getText().toString();
try {
Socket socket = new Socket();
socket.connect(new InetSocketAddress(IPAddr, 8866), 5000);
OutputStream ou = socket.getOutputStream();
ou.write((studentId+password).getBytes("UTF-8"));
ou.close();
socket.close();
}catch (SocketTimeoutException aa) {
//连接超时 在UI界面显示消息
AlertDialog alertDialog = new AlertDialog.Builder(LoginActivity.this).create();
alertDialog.setMessage("服务器连接失败！请检查网络是否打开");
alertDialog.setButton(DialogInterface.BUTTON_POSITIVE, "确定", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
}
});
alertDialog.show();
} catch (Exception e) {
e.printStackTrace();
}
}
}).setNegativeButton("cancel", null).show();

Check for update within android application not on Google Play

I'm pretty much new to android coding, so I'm sorry if I make some mistakes while asking the question.
I'm trying to implement in-app updates for a personal use application and not to be put up on the play store. I've searched my way through stack and found various methods through which that can be achieved. So I tried my own. But the thing is, it doesn't work sometimes, and sometimes it shows wrong information about the update being available. To be more specific, when I compare the curVersionCode to newVersionCode, where curVersionCode = newVersionCode, it still shows that the newer version is available.
Here's My Activity -
public class Test extends Activity {
private Handler mHandler;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.front);
mHandler = new Handler();
checkUpdate.start();
}
}
/* This Thread checks for Updates in the Background */
private Thread checkUpdate = new Thread() {
public void run() {
try {
URL updateURL = new URL("URL TO THE TXT FILE");
BufferedReader in = new BufferedReader(new InputStreamReader(updateURL.openStream()));
String str;
while ((str = in.readLine()) != null) {
// str is one line of text; readLine() strips the newline character(s)
/* Get current Version Number */
PackageInfo packageInfo = getPackageManager().getPackageInfo(getPackageName(), 0);
int curVersion = packageInfo.versionCode;
int newVersion = Integer.valueOf(str);
/* Is a higher version than the current already out? */
if (newVersion > curVersion) {
/* Post a Handler for the UI to pick up and open the Dialog */
mHandler.post(showUpdate);
}
}
in.close();
} catch (Exception e) {
}
}
};
/* This Runnable creates a Dialog and asks the user to open the Update Link*/
private Runnable showUpdate = new Runnable(){
public void run(){
new AlertDialog.Builder(BrowserActivity.this)
.setIcon(R.drawable.ic_launcher)
.setTitle("Update Available")
.setMessage("An update for is available!\n\nOpen Update page and see the details?")
.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
/* User clicked OK so do some stuff */
Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("URL TO THE UPDATE FILE"));
startActivity(intent);
}
})
.setNegativeButton("No", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
/* User clicked Cancel */
}
})
.show();
}
};
Been searching for a few days, still ain't able to find the answer. I'm sorry if this is a basic question but I'm pretty new to it.
Thanks.
EDIT : The code now works just fine. Turns out it requires some time to refresh the version code over the internet text file. Doesn't matter, got experience.

Do you know a better way to write this method?

I created this method to handle 2 different way of creating alert dialog, depending on internet status. Do you know a better way to get the same result? Using .equals() on strings in if-else block do not seem a best-practices way... Am i right?
public void noInternetAlertDialog(String errorMsg) {
String title = null;
String msg = null;
if (errorMsg.equals("none")) {
title = "Connection failded";
msg = "Please check internet connection";
} else if (errorMsg.equals("slow")) {
title = "Connection timeout";
msg = "Connection is slow";
}
AlertDialog.Builder builder;
builder = new AlertDialog.Builder(Main.this);
builder.setCancelable(false);
builder.setTitle(title);
builder.setMessage(msg);
builder.setPositiveButton("Retry", new DialogInterface.OnClickListener(){
#Override
public void onClick(DialogInterface dialog, int which)
{
dialog.dismiss();
downloadDialog();
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
finish();
}
});
AlertDialog dialog = builder.create();
dialog.show();
}

Use strings.xml for your strings to allow localization (Retry, Cancel, "Connection failded", "Please check internet connection", "Connection timeout", "Connection is slow")
If your values represent something create a data type for them. I mean: if your string will report if internet is available or slow, why keep it as String? A String can be everything and convert to something which says directly what values it can assume will improve your code a lot.
public enum InternetStatus {
Offline,
Slow
}
And a == will be faster than a equals call.
If you don't want to use the enum, consider using "none".equals(errorMessage)
String title = "Connection failded";
String msg = "Please check internet connection";
if ("slow".equals(errorMsg)) {
title = "Connection timeout";
msg = "Connection is slow";
}
You can chain calls to the builder and remove the variable dialog because you can call show() directly (If you still need the reference to the AlertDialog, show() still returns it).
You can go with your fantasy and do something like this
.setTitle(errorMsg == InternetStatus.Slow ? "Connection timeout" : "Please check internet connection")
.setMessage(errorMsg == InternetStatus.Slow ? "Connection failded" : "Connection is slow")
but it will make your code a mess if you want to add more InternetStatus.
You could create a method inside InternetStatus which returns the message (if it will be needed in other places too). But it highly depends on the project you are working with. You could an "extension" method which does it for you just where you need it without put it in the enum code (enums can have methods). You should consider every opportunity.
Maybe?
public enum InternetStatus {
Offline,
Slow
}
public void noInternetAlertDialog(InternetStatus errorMsg) {
String title = getString(R.string.internetfailed);
String msg = getString(R.string.checkyourinternet);
if (errorMsg == InternetStatus.Slow) {
title = getString(R.string.connectiontimeout);
msg = getString(R.string.slowinternet);
}
new AlertDialog.Builder(Main.this)
.setCancelable(false)
.setTitle(title)
.setMessage(msg)
.setPositiveButton(R.string.retry, new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
downloadDialog();
}
})
.setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
finish();
}
})
.show();
}

It really is not a good idea to identify a state/result with a string! you should use an enum instead.
enum NoInternetResult {
slow, none
}
and then:
public void noInternetAlertDialog(NoInternetResult result) {
String title = "Connection failded";
String msg = "Please check internet connection";
if (result==NoInternetResult.slow) {
title = "Connection timeout";
msg = "Connection is slow";
}
btw. use strings.xml for you strings like "retry" and "Cancel" (http://developer.android.com/guide/topics/resources/string-resource.html)

Start asynctask automatically when conditions are met

This app searches for places of interest around you when you click a button. The flow is like this:
you click on the button Search
it checks for internet connection, if not, you get a dialog asking
you to enable internet
you click on the button Search
it checks for location services, if not, you get a dialog asking you
to enable location tracking and takes you to the Gps settings screen
then you go back, click on the button Search and an asynctask starts
doing the job (searching and displaying)
What I need to do is eliminate the button Search, so it does everything automatically step by step. So it would be like:
start the app
it checks for internet connection, if not, you get a dialog asking
you to enable internet
when internet enabled, it checks for location services, if not, you get a dialog asking you to enable location tracking and takes you to the Gps settings screen
then it starts the asynctask
I though that an alert dialog would make the activity paused and I could check all the conditions, but it looks like it doesn't. How should I solve this? Feel free to ask for any more details.
Forgot to mention that I only want this done once, the first time the app is started.
Here's my code:
public class MainActivity extends Activity {
//variables
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
lv = (ListView) findViewById(R.id.list);
button = (Button) findViewById(R.id.btn_show_map);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View arg0) {
cd = new ConnectionDetector(MainActivity.this);
// Check if Internet present
isInternetPresent = cd.isConnectingToInternet();
if (!isInternetPresent) {
// Internet Connection is not present
alert.showAlertDialog(MainActivity.this, "Internet Connection Error", "Please connect to a working Internet connection", false);
return;
}
// creating GPS Class object
gps = new GPSTracker(MainActivity.this);
// check if GPS location can get
if (gps.canGetLocation()) {
Log.d("Your Location", "latitude:" + gps.getLatitude() + ", longitude: " + gps.getLongitude());
} else {
// Can't get user's current location
gps.showSettingsAlert();
return;
}
new LoadPlaces().execute();
}
});
}
class LoadPlaces extends AsyncTask<String, String, String> {
/**
* Before starting background thread Show Progress Dialog
* */
#Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage(Html.fromHtml("<b>Search</b><br/>Loading Places..."));
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
protected String doInBackground(String... args) {
Long t = Calendar.getInstance().getTimeInMillis();
while (!gps.hasLocation && Calendar.getInstance().getTimeInMillis() - t < 60000) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
// get the places
return null;
}
protected void onPostExecute(String file_url) {
// dismiss the dialog after getting all products
pDialog.dismiss();
gps.stopUsingGPS();
// display the results
}
}
}
update: I was thinking there might be a better option with a different thread, along the lines of what i wrote below. Or maybe with a service or a receiver.. Any ideas?
Thread th = new Thread() {
boolean allEnabled = false;
#Override
public void run() {
Long t = Calendar.getInstance().getTimeInMillis();
while (!allEnabled && Calendar.getInstance().getTimeInMillis() - t < 120000) {
try {
isInternetPresent = cd.isConnectingToInternet();
if (!isInternetPresent) {
runOnUiThread(new Runnable() {
#Override
public void run() {
alert.showAlertDialog(MainActivity.this, "Internet Connection Error", "Please connect to a working Internet connection", false);
}
});
} else if (!gps.canGetLocation()) {
runOnUiThread(new Runnable() {
#Override
public void run() {
gps.showSettingsAlert();
}
});
} else {
allEnabled = true;
runOnUiThread(new Runnable() {
#Override
public void run() {
new LoadPlaces().execute();
}
});
}
Thread.sleep(20000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
};
th.start();
This version is of course not ok, since it spams one dialog after another.

Usually something like this is solved through several callbacks/entrypoints in your activity. In order to do this you need to build your own AltertDialogs - one to prompt the user to enable internet and one to prompt the user to enable GPS. For the dialogs you will have to set the actions for the NegativeButton and the PositiveButton.
The logic would look something like this:
NegativeButton -> Exit App
Disabled -> Prompt user to enable {
OnCreate -> Check internet { PositiveButton -> Go to Check GPS
|
| NegativeButton -> Exit App
| Disabled -> Prompt user to enable {
*-Enabled -> Check GPS { PositiveButton -> Start AsyncTask
Enabled -> Start AsyncTask
You can implement the "Go to"'s as functions that are called in the OnClickListener of the PositiveButtons.
This is what makes Android a Callback-hell, but I have yet to find a better solution for stuff like this. I hope you can wrap your head around the concept!

One way to do it, is to set the positive button of the alert dialog.
Put each into the positive button click of the alert dialog, such as follows:
new AlertDialog.Builder(this)
.setTitle("Problem")
.setMessage(
"Please Check your *whatever is wrong* ")
.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
//Do the next activity
dialog.dismiss();
}
}).show();
If you want detailed code, then I will. Cheers!

thread not running in background

i am calling this function from the menu and calls the upload(item) function to pass the index of the selected priority.
public void showPriorityDialog()
{
final CharSequence[] priority = {"1 Hour", "12 Hours", "24 Hours", "Cancel"};
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Select Priority");
builder.setItems(priority, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int item) {
if(item != 3)
upload(item);
}
});
AlertDialog alert = builder.create();
alert.show();
}
however, whenever i call the upload function, the thread doesn't run in background, and the OS thinks that the app is not responding due to executing timeout.
public void upload(int priority)
{
final int _priority = priority;
uploadThread = new Thread()
{
#Override
public void run()
{
try
{
super.run();
mHandler.post(new Runnable() {
#Override
public void run() {
try
{
//ftp commands...
}
catch (Exception e)
{
Toast.makeText(getApplicationContext(), e.toString() , Toast.LENGTH_SHORT).show();
}
}
});
}
catch (Exception e)
{
Toast.makeText(getApplicationContext(), e.toString() , Toast.LENGTH_SHORT).show();
}
}
};
uploadThread.start();
}
am i doing something wrong? TIA

When you do mHandler.post(), your entire Runnable executes on UI thread and your background thread just exits. To fix, do FTP before posting to handler. Then do mHandler.post() to have Toast appear. Note that you catch also need to display Toast via post.