listview not updating with notifydatasetchanged() call

Question

This is my code

listview =(ListView) findViewById(R.id.lv1);


    ArrayList<SClass> Monday = new ArrayList<SClass>();

    SClass s1=new SClass();
    s1.sName="samp";
    s1.salary=1000;
    Monday.add(s1);
    temp=Monday;
    adapter = new CustomAdap(this, temp);
    listview.setAdapter(adapter);

The above code works fine.But when i change my code to this

    listview =(ListView) findViewById(R.id.lv1);


    adapter = new CustomAdap(this, temp);

    SClass s1=new SClass();
    s1.sName="samp";
    s1.salary=1000;
    Monday.add(s1);
    temp=Monday;

    listview.setAdapter(adapter);
    adapter.notifyDataSetChanged();

Listview does not show anything.what is the problem?

Answer 1

It looks like you're changing the collection that you initialized adapter with. I would change your code in this way:

// initial setup
listview =(ListView) findViewById(R.id.lv1);
ArrayList<SClass> Monday = new ArrayList<SClass>();
adapter = new CustomAdap(this, Monday);
listview.setAdapter(adapter);

// change your model Monday here, since it is what the adapter is observing
SClass s1=new SubjectClass();
s1.sName="samp";
s1.salary=1000;
Monday.add(s1);

// notify the list that the underlying model has changed
adapter.notifyDataSetChanged();

Note that if your CustomAdap was a subclass of ArrayAdapter, you could also have done

// change your array adapter here
SClass s1=new SubjectClass();
s1.sName="samp";
s1.salary=1000;
adapter.add(s1);

// notify the list that the underlying model has changed
adapter.notifyDataSetChanged();

EDIT: I understand more what you want to do now thanks to your comment. You'll probably want to have the adapter replace its contents with that your different ArrayLists then. I would make your CustomAdap be a subclass of ArrayAdapter.

Then you can utilize it this way:

// replace the array adapters contents with the ArrayList corresponding to the day
adapter.clear();
adapter.addAll(MONDAY);

// notify the list that the underlying model has changed
adapter.notifyDataSetChanged();

Answer 2

Why it works in first code ?

--- Because you are setting the values to temp List and passing it the adapter and it shows it into listview.

Why not work in second code ?

--- Because you are setting temp to adapter far before you set value into temp
second,your adapter class might not getting the updated value when you set new value to temp ..that because temp is not public or not at class level or not static.. Put the temp declaration at root level and try.

And please show your full code as much as required and Logcat if you getting any warnings than also.

Answer 3

Check for a link to your referenced view in the proper xml file. Or at least check for the existence of said xml file.

Answer 4

What adapter are you using? It is clearly a case where your adapter is not getting updated after u set the data in your temp variable.