The Expandable RecyclerView is a library written to allow for an expanded view to be attached to each ViewHolder. To allow for full functionality of a normal RecyclerView in both the parent ViewHolder and the expanded child ViewHolder, the recyclerview has been modified to use two types of ViewHolders, a child and a parent with the ability to customize each separately.
##Project Setup Gradle
Simply add this to your app's build.gradle:
compile 'com.bignerdranch.android:expandablerecyclerview:1.0.3'You can also clone the project and add it as a module to your project.
Clone with:
git clone [email protected]:bignerdranch/expandable-recycler-view.git
Then, navigate inside the directory, clean and build from Android Studio or with
./gradlew clean app:assemble
Now run the sample app on any device or emulator/simulator to view the basic functionality of the list. Code for the sample is located under /app/src/main. All library code is located under /expandablerecyclerview/src/main. The CriminalIntent sample is located under /criminalintentsample/src/main.
Expandable RecyclerView can be used with any stock Android RecyclerView.
What you need to implement:
- A custom adapter that extends
ExpandableRecyclerAdapter - Two custom ViewHolders: a parent ViewHolder that extends
ParentViewHolderand a child ViewHolder that extendsChildViewHolder - The list of objects you wish to display in your RecyclerView must extend
ParentObject.- It is best practice to separate your child data into its own Object, although it is not required.
- A parent layout and a child layout
I have written an in-depth tutorial but it has yet to be published yet. The link will be posted here when available.
Javadocs for the library and sample are available here.
First, create a stock RecyclerView in your layout file and inflate it in your activity/fragment as you would usually do.
Next, create an adapter class that extends ExpandableRecyclerAdapter. Implement the required methods.
Then, create two ViewHolders and their respective layouts. One ViewHolder must extend ParentViewHolder and the other must extend ChildViewHolder. Create their respective views and create variables in these ViewHolders to access those views.
Next, the Object that contains the data to be displayed in your RecyclerView must extend ParentObject
In onCreate or onCreateView of your activity or fragment, create and attach your custom expandable adapter like so:
RecyclerView mRecyclerView = (RecyclerView) findViewById(YOUR RECYCLERVIEW ID);
MyExpandable mExpandableAdapter = new MyExpandableAdapter(getActivity(), YOUR ParentObject LIST);
mRecyclerView.setAdapter(mExpandableAdapter);
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));Inside your ExpandableRecyclerAdapter, you can create and bind your Parent and Child ViewHolders just as you would create and bind ViewHolders in a normal RecyclerView.
Then, define a parent object and implement ParentObject. It is also best practice to create a separate child object to store any data that you need to display in the child view, but it is not required. When you implement ParentObject, you need to create an instance variable, List, to store all the children of the parent object in. The list must be type casted to Object. If it is null or empty, no child will be shown.
public class MyCustomParentObject implements ParentObject {
private List<Object> mChildObjectList;
/**
* Your constructors, variables, data and methods for your Object go here
*/
@Override
public List<Object> getChildObject() {
/**
* You can either return a newly created list of children here or attach them later
*/
return mChildObjectList;
}
@Override
public void setChildObject(List<Object> childObjectList) {
mChildObjectList = childObjectList;
}
}When generating the list of parent objects, you should attach all children to them there. If the children share data with your ParentObject, you can simply create a list of children in the constructor for your parent object or in the getter method for the list.
You can define a custom button, image or view to trigger the expansion rather than clicking the whole item (default). To do this, in your activity or fragment, call myCustomExpandingAdapter.setCustomClickableView(Your Custom View ID) and pass in the id.
If you do set a custom clickable view, you can also set an animation for the view to rotate 180 degrees when expanding and collapsing. This is useful primarily with arrows which signifies for the user to click it to change the expansion. By default the rotation is off. You can enable rotation by calling myCustomExpandingAdapter.setRotation(long durationInMS) in the constructor, below where you called setCustomClickableView(). When setting the rotation, you must pass in a duration in Milliseconds. If you'd like to use the default rotation duration rather than defining your own, call myCustomExpandingAdapter.setParentClickableViewAnimationDefaultDuration() instead. The default rotation duration is 200 ms.
After implementing these, in the activity or fragment that is holding your RecyclerView, simply set the adapter to your custom adapter, and set the layout manager to a new LinearLayoutManager. An example is here:
MyCustomExpandingAdapter myCustomExpandingAdapter = new MyCustomExpandingAdapter(this, objectList);
// Optional animation configuration goes here
mRecyclerView.setAdapter(myCustomExpandingAdapter);
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
To save expanded/collapsed states, inside onSaveInstanceState(Bundle outState) of your activity or fragment, call myCustomExpandingAdapter.onSaveInstanceState(outState). In onRestoreInstanceState(Bundle savedInstanceState(Bundle savedInstanceState), call myCustomExpandingAdapter.onRestoreInstanceState(savedInstanceState). Here is an example of how to override in your activity or fragment:
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState = myCustomExpandingAdapter.onSaveInstanceState(outState);
}
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
mExpandableAdapter.onRestoreInstanceState(savedInstanceState);
}
You can also check out the two sample applications for a full working demo.
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