Question

I have the following problem. I want to read data from a Database in my ActivityA and send one selected String to ActivityB where it should be displayed in a ListView. I’m using intents to do so an it works fine, but I can only display one String. I guess that after reloading ActivityA, the listView is cleared.

So I tried following:
In a separate class called ArrayLst, I defined these two global variables:

public static ArrayList<String> arrayList = new ArrayList<String>();
public static MyAdapter arrayAdapter=null;

And in ActivityA, I’m doing this in the onClick Function:

ArrayLst.arrayList.add(0, myEditText.getText().toString());
ArrayLst.arrayAdapter.notifyDataSetChanged();
Intent intent = new Intent(ActivityA.this, ActivityB.class);
startActivity(intent);

In ActivityB, I want to show the List, so I’m calling this:

lstView.setAdapter(ArrayLst.arrayAdapter);

However, when I click the Button in ActivityA, my App crashes. LogCat says its because of the line

ArrayLst.arrayAdapter.notifyDataSetChanged();

If I delete this line, it doesn’t crash, but I don’t get any results. What am I doing wrong?
Thanks for any help.

ps: since I’m new to Android, please keep the answers simple, so that I can understand it:)

Answer 1

I’d imagine it’s crashing because you never initialize arrayAdapter.

Why are you using a custom adapter (MyAdapter arrayAdapter) ?

In ActivityB you should have an static ArrayList (which it seems you have)

public static ArrayList<String> arrayList = new ArrayList<String>();

Then you’ll need an ArrayAdapter on ActivityB declared in your class global scope

public static ArrayAdapter adapter;

Then in your onCreate you’ll initilize the adapter

adapter = new ArrayAdapter(this, android.R.simple_list_1, arrayList);

If ActivityB extends ListActivity then you’ll call

setListAdapter(adapter);

If ActivityB extends Activity then you’ll call

the following under setContentView()

ListView list = (ListView)findViewById(R.id.YOURLISTID);
list.setAdapter(adapter);

Anytime you add data to the ArrayList then you’ll call ActivityB.adapter.notifyDataSetChanged()

Without knowing what specifically you’re doing I cannot suggest a better idea because it may not be in line with what you’re looking to accomplish.