Listview from arrayadapter filled text file always one update behind - android-arrayadapter

Question

I have a listview that I want to update with information from a textfile (rollcall.txt). Each time rollcall.txt is updated I am calling rollcall() (code below). The data is updated correctly in the text file before rollcall() is called, I have checked. The problem I have is that the listview doesnt show the updated entry until the next time I call rollcall() (I.E it always appears to be one update step behind).
Where am I going wrong?
public void rollcall(){
String[] splitdata = null;
try{
File myFile = new File(Environment.getExternalStorageDirectory() + "/rollcall.txt");
FileInputStream fIn = new FileInputStream(myFile);
BufferedReader myReader = new BufferedReader(
new InputStreamReader(fIn));
String aDataRow = "";
String aBuffer = "";
while ((aDataRow = myReader.readLine()) != null) {
aBuffer += aDataRow + "\n";
}
splitdata = aBuffer.split("`"); //recover the file and split it based on `
myReader.close();
}
catch (Exception e) {
Toast.makeText(getBaseContext(), e.getMessage(),
Toast.LENGTH_SHORT).show();
}
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.logbooklayout, splitdata);
lv1.setAdapter(adapter);
adapter.notifyDataSetChanged(); //called to ensure updated data is refreshed into listview without reload
EDIT: rollcall is called from this method:
public void onClick(View v) {
if (v==badd){
AlertDialog.Builder alert = new AlertDialog.Builder(this);
alert.setTitle("ROLLCALL"); //Set Alert dialog title here
alert.setMessage("Enter data: "); //Message here
// Set an EditText view to get user input
final EditText input = new EditText(this);
alert.setView(input);
alert.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
//You will get as string input data in this variable.
// here we convert the input to a string and show in a toast.
add = input.getEditableText().toString();
try {
File myFile = new File(Environment.getExternalStorageDirectory() + "/rollcall.txt");
myFile.createNewFile();
FileOutputStream fOut = new FileOutputStream(myFile, true);
OutputStreamWriter myOutWriter = new OutputStreamWriter(fOut);
myOutWriter.append(add);
myOutWriter.append("`"); // ` used to split the file down later in lv section
myOutWriter.close();
fOut.close();
}
catch (Exception e) {
Toast.makeText(getBaseContext(), e.getMessage(),
Toast.LENGTH_SHORT).show();
}
} // End of onClick(DialogInterface dialog, int whichButton)
}); //End of alert.setPositiveButton
alert.setNegativeButton("CANCEL", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
// Canceled.
dialog.cancel();
}
}); //End of alert.setNegativeButton
AlertDialog alertDialog = alert.create();
alertDialog.show();
rollcall();
}//end badd
}
Thanks for the help, I am new to using arrayadapters.
Andy

Answer 1

Short answer to your question is everything in UI thread is asynchronous and unless you somehow manage to freeze/lock the whole application you can't make the rest of your UI wait for your alert to grab the input. So long before you press "OK" button in your alert, your rollcall() method is being called from your onClick() function and whatever is inside your .txt file is being read/displayed on your UI, right behind your alert dialog hanging on for you to press one of the buttons, asynchronously.
Maybe the fastest solution to what you want to achieve is to call your rollcall() function somewhere else, after you confirm that your adapter's feeding data has actually been changed. If you must call it from within onClick() function, without questioning your reasons to do so, you should call it inside the try{} block, right after you close the output stream.
Like this:
try {
File myFile = new File(Environment
.getExternalStorageDirectory() + "/rollcall.txt");
myFile.createNewFile();
FileOutputStream fOut = new FileOutputStream(myFile, true);
OutputStreamWriter myOutWriter = new OutputStreamWriter(
fOut);
myOutWriter.append(add);
myOutWriter.append("`"); // ` used to split the
// file down later
// in lv section
myOutWriter.close();
fOut.close();
rollcall();
}
The reason this "works" is you already declared the listener for your "OK" button and whenever you press it, whatever inside your EditText input will be written on file. In order to make it work as before I think you need superhuman skills to write some text on alert dialog and click on button before rollcall() function is called in the same scope.
Obviously the better way to do update the list view is to be able to use adapter.notifyDataSetChanged() but I believe you should call it somewhere else than where you write on your file and in that case your adapter must be declared outside the scope of rollcall() function.
Anyways in order to show how it all goes on I created a simple(rather ugly) android application and put some logs on where the mysterious stuff is happening:
public class MainActivity extends Activity {
private ListView lv1;
private Button refreshButton;
ArrayAdapter<String> adapter;
String[] splitdata;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
refreshButton = (Button) findViewById(R.id.refreshButton);
lv1 = (ListView) findViewById(R.id.someTextViewId);
refreshButton.setOnClickListener(myButtonhandler);
splitdata = null;
}
View.OnClickListener myButtonhandler = new View.OnClickListener() {
public void onClick(View v) {
Log.d("main", "la noliy");
someFunction();
}
};
#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;
}
public void someFunction() {
AlertDialog.Builder alert = new AlertDialog.Builder(this);
alert.setTitle("ROLLCALL"); // Set Alert dialog title here
alert.setMessage("Enter data: "); // Message here
// Set an EditText view to get user input
final EditText input = new EditText(this);
alert.setView(input);
alert.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
// You will get as string input data in this
// variable.
// here we convert the input to a string and show in
// a toast.
String add = input.getEditableText().toString();
try {
File myFile = new File(Environment
.getExternalStorageDirectory() + "/rollcall.txt");
myFile.createNewFile();
FileOutputStream fOut = new FileOutputStream(myFile, true);
OutputStreamWriter myOutWriter = new OutputStreamWriter(
fOut);
myOutWriter.append(add);
myOutWriter.append("`"); // ` used to split the
// file down later
// in lv section
myOutWriter.close();
fOut.close();
if (splitdata.length > 0) {
rollcall(new String("call from inside"));
}
} catch (Exception e) {
Toast.makeText(getBaseContext(), e.getMessage(),
Toast.LENGTH_SHORT).show();
}
} // End of onClick(DialogInterface dialog, int
// whichButton)
}); // End of alert.setPositiveButton
alert.setNegativeButton("CANCEL",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
// Canceled.
dialog.cancel();
}
}); // End of alert.setNegativeButton
AlertDialog alertDialog = alert.create();
alertDialog.show();
Log.d("someFunction", "before rollcall");
Log.d("someFunction", "location: "
+ Environment.getExternalStorageDirectory().getAbsolutePath());
rollcall(new String("call from outside"));
Log.d("someFunction", "after rollcall");
}// end badd
public void rollcall(String message) {
Log.d("rollcall", message);
try {
File myFile = new File(Environment.getExternalStorageDirectory()
+ "/rollcall.txt");
FileInputStream fIn = new FileInputStream(myFile);
BufferedReader myReader = new BufferedReader(new InputStreamReader(
fIn));
String aDataRow = "";
String aBuffer = "";
while ((aDataRow = myReader.readLine()) != null) {
aBuffer += aDataRow + "\n";
}
splitdata = aBuffer.split("`"); // recover the file and split it
// based on `
myReader.close();
} catch (Exception e) {
Toast.makeText(getBaseContext(), e.getMessage(), Toast.LENGTH_SHORT)
.show();
}
int length = splitdata.length;
for (int i = 0; i < length; i++) {
Log.d("rollcall", splitdata[i]);
}
adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, splitdata);
lv1.setAdapter(adapter);
}
}
I put a button and an onClickListener to it. The first time you press the button everything is called, listview is updated and your dialog is hanging on your screen for either of the buttons to be pressed:
And you will see a log like this:
07-26 04:09:20.802: D/someFunction(11273): before rollcall
07-26 04:09:20.802: D/someFunction(11273): location: /mnt/sdcard
07-26 04:09:20.802: D/rollcall(11273): call from outside
07-26 04:09:20.802: D/rollcall(11273): some data
07-26 04:09:20.802: D/rollcall(11273): some other data
07-26 04:09:20.812: D/someFunction(11273): after rollcall
You can see that rollcall() has been called from outside and not inside of your try/catch block since there is also another call from there to rollcall(). But when you press the button your try/catch block will do it's job inside your onClick() function and rollcall() will be called afterwards. Hence your listview wil be updated with new data you just entered in the dialog:
Here is the final part of log right after you press "OK" you can see that rollcall() is being called and it can read the new data:
07-26 04:09:46.347: D/rollcall(11273): call from inside
07-26 04:09:46.357: D/rollcall(11273): some data
07-26 04:09:46.357: D/rollcall(11273): some other data
07-26 04:09:46.357: D/rollcall(11273): new data
Finally, I'm sure there are a lot of ugliness in this whole approach to your problem. Bottom line is you need to know that everything happening in the UI thread is asynchronous and no one is waiting for you to enter data inside your dialog in that onClick() function. You should update your listview somewhere else with a more elegant approach in case your application throws an exception for example around that try/catch block. At least maybe you should add a finally{} block at the end of it and update your listview in there even though the try part fails. Hope this answered your question:)
PS. For those who want to try this at home, remember to provide a TextView id from your layout.xml file to the findViewById() function to get the ListView reference in your code, not an actual ListView id. Yeah, I know...

Answer 2

call adapter.notifyDataSetChanged() everytime you update your adapter, then listview will automatically be updated

Answer 3

I suggest you run rollcall as an asychronous task for 2 reasons. First, it will not stop your UI when rollcall() is running.
Second, you will be able to call onPostExecute(Object o) wher you can call `adapter.notifyDataSetChanged(); '