> > May I ask why we shouldn't modify the view after it has been displayed? > Certainly... It is pretty much a basic principle for good OO design. Your adapter represents the data that needs to be displayed. Your listview item views should do nothing more than use the data it has to decide how it should be displayed.
Let's take a look at how listviews and adapters work in Android... Let's say your adapter has 100 data items in it. In your case each data item consists of a string (item name) and a price (int or float). Even though your adapter has 100 data items in it, the listview does not contain 100 views... It holds on to a few more views than can be displayed on the screen at any given time. So, if your screen can display 10 list view items at a time, the listview itself will only have about 13 or 14 actual views that it uses. When you scroll, it reuses those views to save on memory and the time it takes to create a brand new view. So, what happens if the user clicks on a view and you change the price in the view but not the adapter (data item)? When the user scrolls away and comes back the value that was changed will be lost and the original value will still be displayed. To get around that you could change both the view AND the adapter, but then you are violating the DRY principle: Don't Repeat Yourself. If you are making the same changes in different places then you are probably doing something wrong and there is a better way to go about doing it. Have you ever noticed how hard it is to get a reference to an individual list view item? There is a reason for that... it is only intended to be a display of your underlying data model. Anything that you want to do to change the views should be done in the data model. That way, you change things in one place, call notifyDataSetChanged() and then everything magically updates itself. Now, this means that if you are going to have a complex set of data (meaning typically more than a single type of data in the view) then you will most likely want to subclass one of the existing Adapter classes. I usually subclass BaseAdapter to suit my needs. You also will need to implement your getView() method in the adapter properly. That is where you use the data model to determine how the list view item should be displayed. I would recommend looking up the Android View Holder pattern and implementing that in this method as well, since that will help speed up the scrolling of your listviews. > Does the "no modification" rule apply to moving the views around? > I guess that would depend on how it is done. This case is obviously a little different from what the OP was wanting to do. I've got a ListView object, where I'm using the "TouchListView.java" > adaption to allow the user to resort the items.... > I've not familiar with that so I can't really comment on it. Does this movement qualify as a "modification"? I'm performing data > changes within the Adapter, but the actual view items are getting > moved through the touch interface / view code. > As long as you are updating your adapter and not duplicating code by also manually updating the views you are probably ok. If you are duplicating some code you may want to look and see if there are some ways you can optimize what you are doing. Hope this helps clarify things a bit! Thanks, Justin Anderson MagouyaWare Developer http://sites.google.com/site/magouyaware On Mon, Mar 26, 2012 at 1:21 AM, Danny D <daniel.m.dev...@gmail.com> wrote: > Does the "no modification" rule apply to moving the views around? > > I've got a ListView object, where I'm using the "TouchListView.java" > adaption to allow the user to resort the items.... > > Does this movement qualify as a "modification"? I'm performing data > changes within the Adapter, but the actual view items are getting > moved through the touch interface / view code. > > DD > > On Mar 25, 11:29 pm, Jason Tian <tianji...@gmail.com> wrote: > > Hi, Justin > > > > May I ask why we shouldn't modify the view after it has been > > displayed? > > Cause I've been doing this a lot in my app... > > > > Thanks, > > Jason > > > > On Mar 26, 9:12 am, Justin Anderson <magouyaw...@gmail.com> wrote: > > > > > > > > > > > > > > > > > Modify the data in the adapter and then call notifyDataSetChanged(). > Once > > > the view has been created and displayed on the screen you should NEVER > > > modify it directly. > > > > > Thanks, > > > Justin Anderson > > > MagouyaWare Developerhttp://sites.google.com/site/magouyaware > > > > > On Sat, Mar 24, 2012 at 5:44 AM, Akram <akram0...@gmail.com> wrote: > > > > This listview has an adapter that is linked to a layout for each row > > > > (itemrow.xml) > > > > > > The price value (500-250 300) is a textview > > > > > > How can we access to it, to modify it, once clicked on a button ? > > > > > > Thanks you for the help. > > > > > > lllllllllllllllllllllllllllllllll > > > > > > Android > > > > > > Price: 500 > > > > > > lllllllllllllllllllllllllllllllll > > > > > > Php > > > > > > Price: 250 > > > > > > lllllllllllllllllllllllllllllllll > > > > > > C++ > > > > > > Price: 300 > > > > > > lllllllllllllllllllllllllllllllll > > > > > > -- > > > > You received this message because you are subscribed to the Google > > > > Groups "Android Developers" group. > > > > To post to this group, send email to > android-developers@googlegroups.com > > > > To unsubscribe from this group, send email to > > > > android-developers+unsubscr...@googlegroups.com > > > > For more options, visit this group at > > > >http://groups.google.com/group/android-developers?hl=en > > -- > You received this message because you are subscribed to the Google > Groups "Android Developers" group. > To post to this group, send email to android-developers@googlegroups.com > To unsubscribe from this group, send email to > android-developers+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/android-developers?hl=en > -- You received this message because you are subscribed to the Google Groups "Android Developers" group. 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