How to Instantiate UI objects in reverse?

Question

I'm not entirely sure how to ask this, or what to search for to find answers.

Basically, I'm trying to instantiate prefabs from a list, in reverse. In other words, currently, the first prefab is instantiated at the top of the panel and the last at the bottom, in descending order. I would like them to instead instantiate in ascending order, with the first at the bottom, and the last at the top. Additionally, I would like any new prefabs to bed added to the top.

I have a Generic List of names. From this list, I instantiate the prefabs.

         foreach (var todo in todoList)
         {
             GameObject newTodo = Instantiate(todoPrefab) as GameObject;
             newTodo.GetComponentInChildren<Text>().text = todo;
             newTodo.transform.SetParent(todoPanel, false);
         }
     }

And to add a new prefab I use this

     public void AddTodo()
     {
         string todoFieldText = AddTodoField.text;
         todoList.Add(todoFieldText);    
         GameObject newTodo = Instantiate(todoPrefab) as GameObject;
         newTodo.GetComponentInChildren<Text>().text = todoFieldText;
         newTodo.transform.SetParent(todoPanel, false);
         AddTodoField.text = "";
     }

Not shown is the Input Field the added prefab gets its name from.

I thought about reversing the List itself, but I decided it would probably be better to reverse the way they are instantiated or displayed. That way added a new item to the end of the List will have the desired effect.

Any help is greatly appreciated.

Answer 1

Best Answer

Answer by gameplay4all · Feb 19, 2017 at 07:47 PM

Hey there,

The equivalent to

 foreach (var todo in todoList)

is

  for(int i = 0; i < todoList.Count; i++)

where your var todo is replaced with todoList[i]

You should look up what the syntax is for. Basically it is a start point, condition to continue and an operation to happen at the end of an iteration. Now to reverse the order you use this loop:

 for(int i = todoList.Count - 1; i >= 0; i--)

So now you can use the loop above to go from the last index, todoList.Count - 1, to the first index, 0.

Good luck implementing it!

-Gameplay4all

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Fragmental · Feb 20, 2017 at 04:55 AM 0

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That's an excellent way to display the list in reverse. Thank you for your answer. I was wondering about the best way to do this, and I think this is a better option than trying to use Array.Reverse to reverse the List itself.

Unfortunately, there is still one problem. Every time I add a new element to the list, I would need to delete all the prefab instances and then reinstantiate them. While this would work, I don't like it.

I guess a better question would have been to ask "How can I instantiate parented ui objects above previously instantiated children?"

Answer 2

@gameplay4all I accepted your answer, because it's technically correct, and does answer the question asked.

However, I found another solution which also fixes the problem of pushing newly instantiated children to the top. I created a new question and answered it, for the sake order and to hopefully make it easier to find in searches. This can be found here. http://answers.unity3d.com/questions/1315749/how-can-i-instantiate-parented-ui-objects-above-pr.html

In short, I can use

 newTodo.transform.SetAsFirstSibling();

or

 newTodo.transform.SetSiblingIndex(0);

to push all new instances to the top of the list. More information at the link.

For simply displaying the previously saved generic list in reverse order, I don't know which method is better. I don't know if there are any disadvantages or advantages to either, and both may be equally valid solutions. However, stepping through the array in reverse for the initial population of the the UI list feels cleaner to me so that's what I'm using for now. Then when I add a new object I use SetAsFirstSibling().

How to Instantiate UI objects in reverse?

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