Add/delete value from ArrayList for uniqe values

Question

I'm developing an app that uses ArrayList to fill ListView. I use custom Class for my ListView. I want to add/delete from ArrayList for my Listview.My aim to this app is control list item elements, if it is exist in ArrayList remove or if it is not exist in ArrayList add list item.

In order to explain my situation I have pasted my code below;

It is my custom Class;

public class NDListItem {
    String textdata;
    public NDListItem(String textdata) {
        this.textdata = textdata;
    }
}

It is my method for using my class. Name parameter is coming from another activity. It comes properly. I use for loop for this issue and could not afford to get what I want to do. I read some documentation and found another solution. Using equals and hash-code method for my class may be will do my job but I don't know how to do this usage.

EDIT : Add some explanation and myItems explanation in the second code block.

public void addLayersection(String name) {

//MyList already defined on the scope..
//MyList looks like this
// ArrayList<NDListItem> myItems = new ArrayList<>();

    NDListItem listItem = new NDListItem(name);
  if (myItems.size() == 0) {
        myItems.add(listItem);
    } else {
    if(myItems.contains(listItem))
        {
            myItems.add(listItem);
        }
        else
        {
            myItems.remove(listItem);

        }

    }

    myAdapter.notifyDataSetChanged();
}

EDIT2

I updated my Class for equals method. It works wonderfully but only work first item that I added to ArrayList. I want to this work for every items

public class NDListItem {
    String textdata;

    public NDListItem(String textdata) {
        this.textdata = textdata;
    }

    public boolean equals(Object o) {
        if (o == null) return false;
        //if(!(o instanceof) NDListItem) return false;
        if (!(o instanceof NDListItem)) return false;

        NDListItem other = (NDListItem) o;
        if (!this.textdata.equals(other.textdata))

            return false;
        else


        return true;
    }
}

tutorials.jenkov.com/java-collections/hashcode-equals.html

iced
– iced

2015-03-10 21:19:22 +00:00
Commented Mar 10, 2015 at 21:19 — iced
– iced, Commented Mar 10, 2015 at 21:19
I could not afford to add this usage in my project.

salih
– salih

2015-03-10 21:27:53 +00:00
Commented Mar 10, 2015 at 21:27 — salih
– salih, Commented Mar 10, 2015 at 21:27
you can't add few methods to your custom class?

iced
– iced

2015-03-10 21:29:10 +00:00
Commented Mar 10, 2015 at 21:29 — iced
– iced, Commented Mar 10, 2015 at 21:29
I can add but this always give me some weird errors.

salih
– salih

2015-03-10 21:32:40 +00:00
Commented Mar 10, 2015 at 21:32 — salih
– salih, Commented Mar 10, 2015 at 21:32
still, read that tutorial.

iced
– iced

2015-03-10 21:48:51 +00:00
Commented Mar 10, 2015 at 21:48 — iced
– iced, Commented Mar 10, 2015 at 21:48

user370305 · Accepted Answer · 2015-03-10 21:49:15Z

1

OK, From the details you provided,

As there is no .equals() overridden method available in your Custom Class NDListItem

Your List going to compare object based on references, So just override .equals() method in your custom NDListItem class

Like, (pseudo code only for understanding)

@Override
public boolean equals(Object obj) {     
   NDListItem ndListItemObject = (NDListItem) obj;          
   return this.textdata.equalIgnoreCase(ndListItemObject.textdata);
}

Now, .contains() method will work on Custom Object List as you desired.

Because, your Object comparison made on textdata property.

answered Mar 10, 2015 at 21:49

user370305

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