如何在按钮单击事件上将项目添加到列表视图？

Question

I am coding in Android Studio and having some trouble. I have a button and a listview. When the button is clicked it should add a hardcoded String to the arraylist.

List participants;

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    initParticipants();

    ListAdapter listAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, participants);
    ListView participantList = findViewById(R.id.participantList);
    participantList.setAdapter(listAdapter);

}

public void changeJoinState(View view) {

    boolean checked = ((ToggleButton) view).isChecked();

    if(checked) {

        participants.add("example");

        Toast.makeText(MainActivity.this, "Joined event", Toast.LENGTH_SHORT)
                .show();

    } else {

        Toast.makeText(MainActivity.this, "Left event", Toast.LENGTH_SHORT)
                .show();

    }

}

void initParticipants() {
    participants = new ArrayList<String>();
    participants.add("Creator");
}

Answer 1

After updating the list you should call notifyDataSetChanged to see the updated UI. Make the ListView variable at class level. Also call notifyDataSetChanged after adding string to list.

participants.add("example");
listAdapter.notifyDataSetChanged();

Answer 2

Use notifyDataSetChanged()

void initParticipants() {
   participants = new ArrayList<String>();
   participants.add("Creator");
   participants.notifyDataSetChanged();
}

Answer 3

You need to change if conditional block code with below code

 if(checked) {

    participants.add("example");
     participantList.notifyDataSetChanged();
    Toast.makeText(MainActivity.this, "Joined event", Toast.LENGTH_SHORT)
            .show();

} 

Whenever there is a change in a list, adapter needs to be notified via notifyDataSetChanged() method