Very Quick Sitecore 9. Sitecore Usergroup Chennai at 4: Sitecore Hackathon is coming.
Edit Page Page History In Android development, any time we want to show a vertical list of scrollable items we will use a ListView which has data populated using an Adapter.
The simplest adapter to use is called an ArrayAdapter because the adapter converts an ArrayList of objects into View items loaded into the ListView container. The ArrayAdapter fits in between an ArrayList data source and the ListView visual representation and configures two aspects: Which array to use as the data source for the list How to convert any given item in the array into a corresponding View object Note as shown above that there are other data sources besides an ArrayAdapter such as the CursorAdapter which instead binds directly to a result set from a Local SQLite Database.
Row View Recycling When using an adapter and a ListView, we need to make sure to understand how view recycling works. When your ListView is Using item from item a and to an adapter, the adapter will instantiate rows until the ListView has been fully populated with enough items to fill the full height of the list.
At that point, no additional row items are created in memory. Instead, as the user scroll through the list, items that leave the screen are kept in memory for later use and then every new row that enters the screen reuses an older row kept around in memory.
Here is a visual overview of recycling: Here is another related diagram on view recycling: Refer to this ListView guide for another look at how this works to optimize the performance of your lists. Be sure to check out this Udacity video on view recycling as well.
If you wish to evaluate how fast your ListView is rendering, check out the Profiling GPU tool, which provides a graphical way of visualizing the layout performance.
First, we initialize the adapter: Now, we just need to connect this adapter to a ListView to be populated: If the app requires a more complex translation between item and View then we need to create a custom ArrayAdapter instead.
Using a Custom ArrayAdapter When we want to display a series of items into a list using a custom representation of the items, we need to use our own custom XML layout for each item. To do this, we need to create our own custom ArrayAdapter class.
See this repo for the source code. First, we often need to define a model to represent the data within each list item. Defining the Model Given a Java object that has certain fields defined such as a User class: The naive approach to this without any view caching looks like the following: Another method used is getItem which is already present in the ArrayAdapter class and its task is to simply get the data item associated with the specified position in the data set which is associated with that ArrayAdapter.
Populating Data into ListView Once the adapter is attached, items will automatically be populated into the ListView based on the contents of the array. You can add new items to the adapter at any time with: You can also clear the entire list at any time with: Constructing Models from External Source In order to create model instances, you will likely be loading the data from an external source i.
If you are not using a JSON source for your data, you can safely skip this step. Attaching Event Handlers Within Adapter Within a ListView, we can easily attach event listeners onto any of the views that are item position aware with: Improving Performance with the ViewHolder Pattern To improve performance, we should modify the custom adapter by applying the ViewHolder pattern which speeds up the population of the ListView considerably by caching view lookups for smoother, faster item loading: Making calls to findViewById can be slow in practice, and if your adapter has to call it for each View in your row for every single row then you can often run into performance issues.
Once your ListView has reached the max amount of rows it can display on a screen, Android is smart enough to begin recycling those row Views. If it is not null then we have a recycled View and can just change its values, otherwise we need to create a new row View.
The magic behind this is the setTag method which lets us attach an arbitrary object onto a View object, which is how we save the already inflated View for future reuse.reduce(function, sequence) returns a single value constructed by calling the binary function function on the first two items of the sequence, then on the result and the next item, and so on.
For example, to compute the sum of the numbers 1 through The specification implies that the order in which items are returned initiativeblog.com(),.values() initiativeblog.com() is the same (just as it was in Python 2.x), because the order is all derived from the dict iterator (which is presumably arbitrary but stable as long as a dict isn't modified).
After you locate the item template you intend to use, you can read additional information about the item template and decide whether to download it. To search for an item template online In Solution Explorer, select a target project. Dec 29, · In Brian's example above you see a Binding statement which loads the text portion of each listbox item.
That Binding is the equivalent of "Foreach (thing in my collection) fill the listbox item's textbox with the value of firstname from current thing". Item analysis is a process which examines student responses to individual test items (questions) in order to assess the quality of those items and of the test as a whole.
Item analysis is especially valuable in improving items which will be used again in later tests, but it can also be used to. Reading an Item Using Its Primary Key One common access pattern for databases is to read a single item from a table.
You have to specify the primary key of the item you want.