Android检查值是否等于数组中的值

Question

I have a ArrayList tokens; I am adding values to the array with a listView click. Before i add the value to array i check if the value already exist array. I remove the value is it exists else i will add the the value

This is how i have done, but the values are not being added to the array

ArrayList<String> tokens;
tokens = new ArrayList<String>();
...
....
public void onItemClick(AdapterView<?> listView, View view,
                            int position, long id) {
        Cursor cursor = (Cursor) listView.getItemAtPosition(position);
        String selectedtoken = cursor.getString(cursor.getColumnIndexOrThrow("ContactToken"));

        for (int i = 0; i < tokens.size(); i++) {
                if (tokens.get(i).equals(id_To_Search)) {
                    tokens.remove(i);
                }
                else {
                    tokens.add(selectedtoken );
                }
            }
    }
...
...
Log.i("array: ", tokens.toString()); // No values in the array

Answer 1

You are not adding when you initially have 0 tokens.

Change to:

boolean removed = false;
for (Iterator<String> iter = tokens.iterator(); iter.hasNext(); ) {
    if (iter.next().equals(id_To_Search)) {
        iter.remove();
        removed = true;
    }
}
if(!removed) {
   tokens.add(selectedtoken);
}

Answer 2

You can simply check the existence using contains method.

if(!tokens.contains(id_To_Search)){
    tokens.add(selectedtoken);
} else {
    tokens.remove(selectedtoken);
}

Answer 3

You're checking for each element in your array if it's the item you're going to store/delete, and then doing the proper operation.

You should find first if you're element exists in the whole array, and then adding or deleting it.

Try something like this:

public void onItemClick(AdapterView<?> listView, View view,
                        int position, long id) {
    Cursor cursor = (Cursor) listView.getItemAtPosition(position);
    String selectedtoken = cursor.getString(cursor.getColumnIndexOrThrow("ContactToken"));

            if (tokens.contains(id_To_Search)) {     
               tokens.remove(id_To_Search);

            }
            else {
                tokens.add(id_To_Search);
            }
}

Answer 4

If your list is empty, you never go into the loop, so you'll never call add . If you do have any tokens to start with, you're either adding or removing the new token for each existing token which isn't what you want.

I suspect you want:

int existingIndex = tokens.indexOf(selectedToken);
if (existingIndex == -1) {
   tokens.add(selectedToken);
} else {
   tokens.remove(existingIndex);
}

Alternatively, you could use a Set<String> with:

// Speculatively try to remove it... and add it if you couldn't remove
boolean removed = tokens.remove(selectedToken);
if (!removed) {
   tokens.add(selectedToken);
}

Also note that you're currently testing for id_To_Search but then adding selectedToken - this answer assumes you actually meant to use selectedToken in both places.

Answer 5

当tokens.size（）为0时，for循环将不会执行。因此，您将永远不会添加令牌，因为最初的令牌列表为空。