The root element is a merge tag, which means that during inflation, each of the children of that tag will be added as children of the parent argument passed to the inflate(.) method in the constructor. Item is the generic model object that represents data within our list using three properties: an image URL, a title and a description.
Instead of creating a generic view, a holder class and an Adapter implementation that knows too much about how to wire them all together, we will use a subclass of RelativeLayout for the root view of our custom layout. So, rather than complaining about it all the time, I’ll propose an alternative: subclassing! Customizing Using a Subclass
It violates encapsulation, since the adapter/holder has to know about the internals of the view representing each item in the list. The view’s tag property requires casting to the correct holder type, which feels kludgy. The “holder” class is typically just boilerplate code and creating it/setting it up is a chore. It puts too much responsibility in the Adapter’s getView(.) method. I don’t like this pattern, for several reasons: Reuse (and cast) the holder object for reused row views. Set the instance of the holder as the top-level view’s tag with setTag(Object). One implementation you see described all over the Internet is called “the holder pattern.” In a nutshell, it entails these steps:Ĭreate a “holder” class with fields to store child views of the row.įor each new inflated row, create a holder instance and assign its fields to the results of calling findViewById(int) for each child view. Since this is such a common problem, patterns have emerged. Take advantage of view recycling when scrolling.Įfficiently identify and populate child views with data. Use a custom layout to define the arrangement of child views. When creating custom views for a ListView or other AdapterView, we have a few requirements: You can find the code for this example project on GitHub. You can see what it looks like in the screen shot below. The Goalįor demonstration purposes, we’ll create a typical simple custom ListView row with an ImageView and two TextViews arranged inside a RelativeLayout parent.
In this post, we explore an alternative that uses a subclass of RelativeLayoutto encapsulate the customization work. But the Holder pattern is clumsy and full of boilerplate, and we can do better. When that happens, you’ll probably reach for the Holder pattern. Import Android programmer will at some point customize a ListView row by creating their own layout and populating it with data. Get value of selected item in listview in android. What i am doing in this project : I am creating string array and set that array items into listview after that setting up setOnItemClickListener() function on listview and Print toast message with list selected element.
0 kommentar(er)
