I have a simple listView with simple adapter and I am getting a new live content (it means data with changed items) every 5 sec. I have to update some rows with new values, so I clear adapter and addAll in list, but then all list is freezing and scrolling up.
If it's a short list, all is work good, the problem becomes when I have long list with scroll.
Is there better solution for my task? How could I monitor only changed rows and redraw there?
Instead of ListView use RecyclerView. RecyclerView allows to refresh and add individual elements to list.
Adapter method item added at position
So my solution is. As I have abnormal list (I'm getting response from back-end with different values for each row, I must to group it and generate unique layout for each row), so I've used a TableLayout, I generated each row and put it to Map, when I catch new response I check old value with new one and if there are different, I take View from Map and bind new data.
Related
My problem is similar to ListView getChildAt returning null for visible children, but despite searching I cannot find a solution.
I have a ListView with a Scroll. The ListView has 10 items, 7 of which are visible and 3 are hidden by scroll. I also have an external method (out of adapter) that must get all of the children from this ListView (e.g. using getChildAt()).
I need all 10 of the items, but the last 3 are null objects. I've tried code like the following:
getListView().smoothScrollToPosition();
But this doesn't work.
I think that I don't need to post the rest of my code, as the description says everything?
As you have already seen you can't get all the child row views from a ListView simply because a ListView holds only the views for the visible rows(plus some recycled rows but you can't reach those). The correct way to do what you want is to store whatever data in the adapter's data and retrieve it from there.
But the ListView doesn't keep the current values from RadioGroup in
running time.
I've seen that you have some problems with this so I've adapted some old code to build a basic example, code that you can find here.
I don't think so you need to add scroll view for a listView. Scroll automatically works on ListView. Try your application without adding scroll view and I'm sure it'll work as you needed.
The reason those children are null it's because they really do not exist and they will never exist, if only 7 children are on the screen at one time, the system will only create 7 and re-use by passing the convertView back to the adapter getView() method.
If you want to grab information regarding your whole dataset you should search on the dataset itself, instead of the views on the screen. E.g. if it's an ArrayAdapter, loop the array; if it's a CursorAdapter, loop the cursor; etc.
The non-visible children of a listView don't actually exist. When they become visible, one of the redundant views is recycled or a new view is generated. So you can't actually access all the views. Why do you want to? Whatever changes you want to make should be made to the data that populates the views rather than the views themselves.
There are a few point that you need to take care of:
1. List view provides inbuilt scroll functionality, So don't use Scroll view. It will only mess up things.
2. List view doesn't contain ALL the children. When you scroll it, it creates only visible items on run time.
3. If you want to get all the children altogether, Better keep an ArrayList of the child objects that your list has. You can add or remove children to this ArrayList as per requirement.
I am building an Inventory application. The items are shown in a grid view and each cell of the grid view also has a TextView in the upper right corner that displays the available quantity of the item. The user can single click on the gridview cell to increase the quantity or long click to decrease it.
I am currently using a class derived from SimpleCursorAdapter to display the data, but I am not sure about how to update the quantity in the DB. I am afraid that if I write directly to the DB and then create a new cursor and change cursor that the application might become bogged down if the user clicks repeatedly (say to add 10 items)
I have considered copying the data from the query cursor to an array in the Activity and then using an ArrayAdapter but this seems kludgy.
I have also thought about creating an array in my SimpleCursorAdapter which would cache items that have been modified and then save those items when pausing...
Is there a better way? A more Android way?
I guess this comes down to: what is the best way to make rapid changes in the DB and UI?
I don't know much about Cursors in this regard, but I would create a custom ArrayAdapter based on a model object rather than a Cursor. That's just a personal preference, but by doing this I don't have to make any assumptions about the Cursor implementation or know it inside and out.
Let's say you're displaying a collection of type Item in your grid. I would create a class called ItemsList that derives from ArrayList<Item> and my adapter would derive from ArrayAdapter<Item>. The reason you create a wrapper around the ArrayList is that you can allow the user to interact with it freely and mark it as "dirty" and allow it to update the database asynchronously. This way, you just call notifyDataSetChanged() on your adapter and you don't have to think about the overhead of updating the db...you've separated interacting with the collection being displayed and the process of updating the persistent storage.
Btw...this video is a must when working with ListViews and Adapters if you haven't already seen it:
http://www.youtube.com/watch?v=wDBM6wVEO70
You could use a regular listView and a regular Adapter with a list (arraylist) of items in it. Every time user clicks or long clicks you can edit the list in your adapter and notifyDataChanged() which will reflect the list changes on your listView. If you want to keep your list after user quits your application you can use either database(for bigger amount of data) or preferences (for smaller data amount).
I want to have a Button that when clicked, removes all the checked items in the ListView. I already have all the xml items set up, I just don't know how to write the java code.
The ListView displays data that comes from an Adapter. In order to remove items from the view the item needs to be removed from the Adapter and the view notified. In android the Adapter notifies the view by calling notifyDataSetChanged().
How to remove an item from the adapter depends on your particular adapter. The SimpleCursorAdapter gets its data from an underlying Cursor. To remove an item, the item should be removed from the underlying Cursor. For example using a SQLiteCursor a row in the database needs to be deleted.
If you use the ArrayAdapter just call remove(T object) on the adapter. It will automagically call notifyDataSetChanged() for you.
update:
I saw the code at git hub. Here are some pointers as how to get your app working as soon as possible.
Try refactoring your code in to smaller graspable parts. Start with extracting some methods to give parts of the large method understandable names.
The problem is that there might by hundreds of rows in the database and only enough views to fill the screen. Nowhere is it remebered what rows are checked, hence its not possible to remove them. You probably need to extend BaseAdapter or SimpleCursorAdapter to hold the state (checked or not) of the rows. Read up on the excellent android documentation.
My point here is there is a distinction between the view, your CheckBox, and the model containing the data to display. So check out Model-View-Controller. You can ignore the concept of controller for now.
I have a ListView with an ArrayAdapter providing the data. I'm adding paging, so when you scroll to the bottom it loads more rows.
But as I'm using an array I'm finding a problem. I can't extend the array as the size is obviously fixed, and if I create a new one, the ListView either ignores the new items (notifyDataSetChanged), or (if I refresh the list with the new array) it jumps to the top.
What's the usual way to do this? Use a different collection type? Use a large array with capacity for the maximum number of rows? Or is there a way to notify an adapter the dataset has changed and it actually works (notifyDataSetChanged() is not working in my scenario, probably because the array hasn't just changed, it's a completely different one, so the notify is probably working with the old one). Or should I set the adapter up with the new larger array, and jump it to the right position?
You say ArrayList in the title, but you're talking about just an Array. Try using an ArrayList, you can add as many items as you need to with the ArrayList.add() method. Am I misunderstanding you, maybe?
So I am having a problem with the different pieces of that make up my ListView. I put them into an ArrayList and use a custom ArrayAdapter to hook up to the ListView, which I have done before so I don't believe there is a problem there. Initially the list seems to have the pieces in the correct order, but then I will scroll down the list and the contents will then load in incorrect order. I then scroll back up and everything is jumbled. Has anyone run into this before?
Thanks
-Jake
Yes your problem is related to the fact that List reuses the views for each row. So say your list can see 5 items, but your ListAdapter has 15 things in it. Android will create 5 + 1 instances of your row view instead of 15. One for each row in the list + 1 for when half of the top and bottom can be seen. When a row is moved out of the visible area the List will recycle that view instance for another row instead of creating a new one. If you don't properly reset all of the user interface components every time you'll get artifacts from other rows showing up. You must make sure that every time you bind your data from the objects in your array list to the view you set every field every time.
For a better description of this see
http://www.youtube.com/watch?v=N6YdwzAvwOA&feature=related