I have list/rows of checkboxes inside recycle view. In my case, the user can only select 3 checkboxes out of many. As soon as the user selects the third checkbox, I want to disable rest of the checkboxes in different rows.
I am capturing selecting/deselecting checkboxes inside adapter class.
As far as I know, I can enable/disable checkboxes inside onBindViewHolder class.
But in my case, I want to enable/disable checkboxes, after they have been rendered.
One of the approaches I can think is, to call notifyDataSetChanged(); from Activity class and then rerender all the recycled view.
But I hope there is the better way than doing this, inside the adapter class itself.
ps: I am new to android/java.
notifyDataSetChanged() will defently work in your case.
Please note that you don't have to call this method from the Activity.
You can call it internally within your adapter after the third checkbox was selected.
From the top of my head, One way to do this would be to store the "checked" positions indide an array within the adapter, then inside onBindViewHolder() check to see if the current position should be enabled or disabled.
In your model class you can have a boolean variable that decide whether the item should be enabled or not and another boolean variable to keep track of the checked state, or if the item is checked or not. In onBindViewHolder check the variable to enable or disable the item.Keep track of the selected items and then after every check and uncheck, check if the selected items exceeds the limit. Then loop through your items and then check if the item is checked or not. if the item is not checked set the value to false and after the loop send a notifyDataSetChanged() and in onBindViewHolder() check for the value and enable or disable the item/checkbox
You can use SparseBooleanArray to record all the changes for each item based on their positions.
You can use the following method in RecyclerView adapter:
notifyItemInserted(int)
notifyItemRemoved(int)
notifyItemRangeChanged(int, int)
notifyItemRangeInserted(int, int)
notifyItemRangeRemoved(int, int)
Read more at RecyclerView.Adapter.
Only use notifyDataSetChanged() as the last resort. Because calling notifyDataSetChanged() will force the views to rebind and relayout. As in the documentation says:
void notifyDataSetChanged ()
Notify any registered observers that the data set has changed.
There are two different classes of data change events, item changes
and structural changes. Item changes are when a single item has its
data updated but no positional changes have occurred. Structural
changes are when items are inserted, removed or moved within the data
set.
This event does not specify what about the data set has changed,
forcing any observers to assume that all existing items and structure
may no longer be valid. LayoutManagers will be forced to fully rebind
and relayout all visible views.
RecyclerView will attempt to synthesize visible structural change
events for adapters that report that they have stable IDs when this
method is used. This can help for the purposes of animation and visual
object persistence but individual item views will still need to be
rebound and relaid out.
If you are writing an adapter it will always be more efficient to use
the more specific change events if you can. Rely on
notifyDataSetChanged() as a last resort.
Related
I have a problem regarding the back button feature together with RecyclerView, my goal is to emulate the behavior in the Contacts application, where you press and hold (long press) an item in the RecyclerView and a check box appears behind the item(s) (all of them). Then, when you press the back button, all the check boxes disappear.
Regarding the information I provided we can break the problem in two parts:
First, we need to solve the long click problem, which I suspect we can use
NotifyDataSetChanged() together with hiding the check boxes in the XML so that we can switch between checkbox.setVisibility(VISIBLE) and checkbox.setVisibility(GONE).
Lastly, and this is the hardest part for me, I would like that, when back button is pressed, all the check boxes disappear, instead of leaving the app.
Thank you in advance and sorry if the problem is not understandable, as this is the first time I am posting a problem and English is not my native language.
What you are describing is known as Contextual Action Mode.
You'll notice, that when you long press the item the toolbar (action bar) on top changes and shows the number of selected items and a set of action you can apply to the selected items.
Pressing the back button then cancels the action mode.
It is beyond Stackoverflow's scope to explain the whole action mode system, but you can simply search for it in the internet.
Here is a tutorial for beginners, for example.
I can give you a better answer if you post your code.
You'd probably want your adapter to contain a list of selected items. If the list has any elements, you show the checkboxes and check the ones that correspond to the list. If it is empty, you don't do that. You're correct about notifying data set changed. Long press on an item would add that item to this list. Then when your adapter re-laid out your items, it would show the checkboxes since that list would not be empty.
For the second issue, you'd want to override onBackPressed() in your activity. Then you can have some code like:
public void onBackPressed() {
if (adapter.hasItemsSelected()) {
adapter.clearSelection()
} else {
super.onBackPressed()
}
}
You'll need to write these adapter methods. hasItemsSelected should check to see if there are elements in the selected items list and clearSelection should clear the list and notify data set changed.
I use adapter in RecyclerView. Each item contains a ProgressBar. Since progress speed is sometimes very high, a fragment permanently call notifyDataSetChanged(), which initiates update adapter. But there is one unpleasant feature: at this time ViewHolder doesn't respond to a click and user can't open the item, while progress speed will not decrease. Is it possible to solve this problem?
notifyDataSetChanged actually redraws the list for you. So click on the list item at that instant may actually refer to the content which was available before you refreshed the adapter contents. Hence its a good thing that click isn't enabled. Having said that, the refresh usually happens so quick that the user won't see a visible lag. Hence please go through you getView() method in the adapter if there is an intense or time taking process in the adapter implementation. Hope this helps! :)
how to update ReyclerView adapter without make OnCreateViewHolder(...) being called?
Because when i do
mRecyclerView.getAdapter().notifiItemChanged(position)
it goes inside OnCreateViewHolder(...) what i don't want to. The reason why i don't want is because I have expanded item view and onCreateViewHolder(...) will reinflate it so make collapsed. I only want to OnBindViewHolder(...) being called
Have anyone faced with it?
UPD:
Just found that OnCreateViewHolder(...) is called only one first time, in all next times it's not being called. What is the reason?
t
You could add a boolean isExpanded to your data objects in your dataset, and then in the onBindViewHolder method check whether isExpanded is true, if so expand the view programmatically. (and ofcourse don't forget to switch the boolean when expanding/collapsing the view)
This is the whole point of RecyclerView : it handle a pool of view holders, which are created once (calling OnCreateViewHolder()) then reused (or recycled, hence the view name) as much as possible via OnBindViewHolder().
OnCreateViewHolder() is used to create the views, while OnBindViewHolder (re)set the views state (like text content, selected state, ...)
It follows that any state associated with an item (like the expanded / collapsed state) should not be stored in the ViewHolder. You can for example use a private List in the adapter.
Is it somehow possible to force adapter to redraw only specific item?
Currently if I want to redraw the list, I call notifyDataSetChanged() which re-iterates through all the data-set and redraws all elements. What if I know exactly which element was updated and I want to redraw only that one?
notifyDataSetChanged() is not for redrawing elements, it is for notifying the adapter, that the elements have changed in some way, for example there are more elements, or their data is set from an other class etc. Of course, the ListView (or other class), to which the adapter is connected will redraw the elements, becuase the Adapter is forced to tell him, its dataset is changed.
As Yume117 commented, for redrawing you can call one View's invalidate() method (or even better postInvalidate()),
postInvalidate():
Cause an invalidate to happen on a subsequent cycle
through the event loop.
public void invalidate ()
Added in API level 1
Invalidate the whole view. If the view is visible, onDraw(android.graphics.Canvas) will be called at some point in the future. This must be called from a UI thread. To call from a non-UI thread, call postInvalidate().
You can call these methods on one view in the Adapter's getView() method, or only call invalidate on the ListView (or other view) itself, and it will only redraw the visible elements.
You can create singletone object with Map. And then put every View of your object to this map. And after all, you can change this object, redraw your specified View (you have to know position) and then call notifyDataSetChanged().
There is no such method out of box, which is not so bad as not whole dataset gets re-iterated and not all elements gets redrawn, but just currently visible ones. These are usually not so many.
I tried to found a method, but no results. I want a ListView like below, and when I click on an element, like "Word", it'll be like this picture :
Is it possible ?
What you described is what an ExpandableListView does.
Basically it's like a listview so you'll still have to create your own adapter, but it lets you click a row to inflate a bigger item that you can then stuff your text into.
I would recommend creating your own class that extends ArrayAdapter or BaseAdapter. Then you can make use of the getView() method that gets called every time the screen gets redrawn for the user. You can then design multiple views for each selection and choose which one to display in the getView() function. So when the user selects an item, you set a flag in your custom class, and then notifyDataSetChanged() and you're good to go!