有没有办法只获取 setOnItemClickListener 的单个值，而不是在多次单击选项时获取多个值

Question

我有一个核对清单，我想将列表中所有选中的项目发送到Firebase数据库。我已将其发送到数据库，但有一个问题。如果选择、取消选择并再次选择该项，则该值将发送到数据库两次。

    listView.setAdapter(adapter);
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> adapterView, View view, int i, 
    long l) 
    {
       String selectedItem = ((TextView) view).getText().toString();
       selectedItems.add(selectedItem);
       if (unselectedItems.contains(selectedItem)) {
       unselectedItems.remove(selectedItem);
    }
    }
    });
    public void showSelectedItems(View view) {
    FirebaseUser user = mAuth.getCurrentUser();
    String presentStudents = "";
    for (int i = 0; i < selectedItems.size(); i++) {
        dbPresentRef.child(selectedItems.get(i)).push().setValue("Present");
        presentStudents += "-" + selectedItems.get(i) + "n";
    }
    }

Answer 1

只需添加一个if条件，然后再像这样添加selectedItem selectedItems列表。

listView.setAdapter(adapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int i, 
long l) 
{
   String selectedItem = ((TextView) view).getText().toString();
   if(!selectedItems.contains(selectedItem)){
    selectedItems.add(selectedItem); 
   }

   if (unselectedItems.contains(selectedItem)) {
   unselectedItems.remove(selectedItem);
}
}
});
public void showSelectedItems(View view) {
FirebaseUser user = mAuth.getCurrentUser();
String presentStudents = "";
for (int i = 0; i < selectedItems.size(); i++) {
    dbPresentRef.child(selectedItems.get(i)).push().setValue("Present");
    presentStudents += "-" + selectedItems.get(i) + "n";
}
}