I have taken an example code for implementing a RecyclerView, but trying to transpose it to work in a Child Fragment in my app.
The code is under 'Create Lists - examples'
Creating Lists and Cards
I run into trouble with my adapter..
public static class ViewHolder extends RecyclerView.ViewHolder {
// each data item is just a string in this case
public TextView mTextView;
public ViewHolder(TextView v) {
super(v);
mTextView = v;
}
}
> #Override
> public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
> int viewType) {
> View v = LayoutInflater.from(parent.getContext())
> .inflate(R.layout.my_text_view, parent, false);
> ViewHolder vh = new ViewHolder(v);
> return vh;
> }
First, it doesn't build, complaining that I am calling constructor ViewHolder with a View, when the constructor is expecting a TextView.
Looking at the code, I agree!
But this is an official example so it must be right?
So what is different to my version compared with the example?
Two things that I can think of...
1)
the layout my_text_view is not given in the example, so I made my own. Did I make it right?
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<TextView
android:id="#+id/t_title"
android:title="title"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
2)
I am calling the adapter from my child fragment, and the example was not written with fragments in mind.
I've probably bitten off more than I can understand there.
Still, working this through, as far as i understand.
The 'parent' coming into my OnCreateViewHolder, is my RecyclerView ?
'v' should be the LinearLayout of my 'my_text_view' ?
'ViewHolder' should end up being a class with property mTextView equaling the TextView from my xml.
I just don't see how I go from v=LinearLayout , to TextView??
Anyone like to help explain to this noob ??
That example is not very good. It looks like two different projects spliced together. It should be something like this:
public class MyAdapter extends RecyclerView.Adapter {
public static class ViewHolder extends RecyclerView.ViewHolder {
public TextView mTextView;
public ViewHolder(View v) {
super(v);
mTextView = (TextView) v.findViewById(R.id.t_title);
}
}
#Override
public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.my_text_view, parent, false);
ViewHolder vh = new ViewHolder(v);
return vh;
}
}
To explain this segment:
onCreateViewHolder is the method that will be called any time the RecyclerView needs to create a new type of ViewHolder. This may get called only a dozen or so times to get enough Views to cover the screen or it may be called quite a few times if you have many view types.
The parameter parent in this case will be the RecyclerView that accompanies it. Why not just make it RecycerView? Because Google designers decided it should be a ViewGroup. Also it's an Adapter pattern so the only guarantee you're supposed to have is that it's a ViewGroup (i.e., may not be a RecyclerView so you shouldn't build the Adapter with that assumption). Realistically, it will pretty much always be a RecyclerView though.
The parameter int viewType is to tell you what kind of View you're building. This is determined if you override getItemViewType() method of the Adapter. You don't need to worry about this if you only have one type of View though.
For the ViewHolder, this is to basically cache the different types of Views in your layout. These can be ImageView, TextView, etc. These will be "recycled" constantly as the user scrolls so you're not always creating them. That way, you only have to update the Views with the current information. In this case, there's just a title. The ViewHolder passed in bindViewHolder will be where the actual updating happens. This is called all the time, so there's no need to initialize the Views in onCreateViewHolder. Just need to create them.
Related
I have fragment "Incoming" on one slide of a viewpager. This fragment contains a RecyclerView populated with custom-relative-layouts. The LinearLayoutManager orientation is Vertical.
I have a second fragment "Find" on the next slide of the said viewpager. "Find" will consist of two recyclerviews. It will have a Horizontal recyclerview filled with cardviews (fast loading of profile pictures). Underneath that, I am loading more slowly another recyclerview with a custom-relative-layout, the same as in the "incoming" fragment.
Does that make sense? I'll elaborate some more:
The question is for these three recyclerviews, should I declare a new RecyclerAdapter for each one? The reason I ask is that they'll all have unknown variable item_counts.
Here is the RecyclerAdapter I have for "Incoming":
public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder>{
private Context mContext;
public RecyclerAdapter(Context context, List<Incoming> items) {
mContext = context;
}
public static class ViewHolder extends RecyclerView.ViewHolder {
public ViewHolder(View v) {
super(v);
// Define all of the components in the view
}
}
#Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
LayoutInflater mInf = LayoutInflater.from(mContext);
View customView = mInf.inflate(R.layout.item_layout_incoming, parent, false);
final ViewHolder vh = new ViewHolder(customView);
return vh;
}
#Override
public int getItemCount(){ return 6; } // THIS IS TEMPORARY; WILL BE VARIABLE
#Override
public void onBindViewHolder(ViewHolder holder, int position) {
// Replace contents
}
For my criteria, should I create another Adapter for my horizontal-cardview-recyclerview? It seems repetitive, but otherwise, how would I handle either inflating cardview or item_layout_incoming?
Seems like there should be a DRY way to do this, without hits to performance. Thanks
You are using fragments so you will create 2 objects of that class. So it's the same thing. you just reduce compiler load by reducing the task of loading the new class into memory and then create its object.
It's better to use two different Adapter because of 2 reasons.
Your code will become ugly I mean so much congested and so many if
else condition.
In future, if you need to change something in layouts then again it
will affect all objects if same adapter class.
So my advice do developer friendly code and create two classes.
I've got RecyclerView list where items views are created partially from layout in .xml file (let's say header) and partially programmatically based on list items. I'm using few different itemsViewTypes.
Which approach is better?
1) to generate Views in adapter:
#Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.recyclerview_item, parent, false);
MyViewHolder holder = new MyViewHolder(view);
createAndAddNewViews(barsHolder);
createAndAddNewViewsBasedOnSomeParams(param1, param2);
// both createAndAddNewViews() and
// createAndAddNewViewsBasedOnSomeParams() are Adapter methods
return holder;
}
2) to generate Views in ViewHolder:
public MyViewHolder(View itemView) {
super(itemView);
... // findViewsById and so on
createAndAddNewViews();
createAndAddNewViewsBasedOnSomeParams(param1, param2);
// both createAndAddNewViews() and
// createAndAddNewViewsBasedOnSomeParams() are ViewHolder methods
}
Of course my examples are simplified just to show the case.
From code reading perspective it's better to have views generation logic inside holders. Every different item has it's own creation code inside one class. I don't have to deal with every single item in Adapter. But I'm not sure if it's ok simply from ViewHolder pattern design and from memory and speed optimization perspective.
I wonder which approach you consider as better and why.
Edit: Does the same applies for modifying view (onBindViewHolder) and methods in Adapter/ViewHolder?
Thanks!
Performance wise it's the same in both the approaches. If you have different ViewHolders for different itemTypes you can do in in ViewHolder to segregate the code belonging to a certain ViewHolder at one place
I'm using a custom CompoundView which extends LinearLayout to display items of a RecyclerView. Each item displays an article which contains multiple paragraphs and images. The CompoundView adds TextView or ImageView dynamically based on the data attached by CompoundView.setData(List<DataPiece> pieces), the number of which is unknown before data is attached. Each DataPiece object tells CompoundView whether it's a piece of text or an image. And here is the code for CompoundView.setData(List<DataPiece> pieces):
public void setData(List<DataPiece> pieces) {
removeAllViews();
for (DataPiece dataPiece : pieces) {
switch (dataPiece.getType()) {
case IMAGE:
ImageView imageView = new ImageView(getContext());
...
addView(imageView);
break;
case TEXT:
TextView textView = new TextView(getContext());
...
addView(textView);
break;
}
}
}
In the RecyclerView.Adapter.onBindViewHolder(), the data is attached to CompoundView by calling MyViewHolder.compoundView.setData(...). And it works fine when the RecyclerView is created.
However, for a CompoundView item with multiple ImageViews and TextViews, when I scroll away from it and then scroll back, the scroll becomes heavily unsmooth.
I guess it's because removeAllViews() in setData() is called, and the CompoundView creation for-loop is executed again by the recycler. But I don't know how to avoid this.
And I also wonder why the scroll is always smooth when using TextView(with Images) in a RecyclerView even it's recycled too.
Thanks in advance!
There are multiple considerations that could go into deciding what the best approach might be.
First, do you have an idea about the maximum number of items in the recycler's list? If it is just a handful, maybe you could ditch the RecyclerView approach and just add your CompoundView into a container hosted by a ScrollView.
Secondly - is the layout of each item fairly complicated (a.k.a. are there many TextViews, ImageViews etc. in it)? If yes, maybe you could take an approach that would resemble an ExpandableListView - show a summary as each list item and expand to the full layout of the item on click.
Thirdly - if none of the above is acceptable and you still want to go the current approach - don't construct/add your view in the binding method. Do it in the onCreateViewHolder, when the system expects you to construct your view (I don't know for sure but by the time you're called on onBindViewHolder your view might have been already added to the hierarchy and any hierarchical change to it has a ripple effect on its containers - but don't take my word for it, I don't actually know the view is already added, it is just an assumption). You will have to assign each item a different type, so that in onCreateViewHolder you could match the view type with the supporting data (for the addition of the corresponding number of child views); create the view from scratch each time - this way you don't need to call on removeAllViews. Something like(I left out parts of the adapter that are not relevant to the case):
public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
ArrayList<DataPiecesList> mItems;
public RecyclerViewAdapter(ArrayList<DataPiecesList> items) {
mItems = items;
}
#Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
CompoundView compoundView = new CompoundView();
List<DataPiece> dataPieces = mItems.get(viewType);
for (int i = 0; i < dataPieces.size(); i++)
{
// construct TextView or ImageView or whatever
compoundView.add(child);
}
MyViewHolder view = new MyViewHolder(compoundView);
return view;
}
#Override
public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int i) {
CompoundView compoundView = viewHolder.itemView;
DataPiece dataPiece = mItems.get(i);
for (int j = 0; j < compoundView.getChildCount(); j++)
{
compoundView.getChildAt(j) <- dataPiece.get(j);
}
}
#Override
public int getItemViewType(int position) {
return position;
}
#Override
public int getItemCount() {
return mItems.size();
}
public class MyViewHolder extends RecyclerView.ViewHolder {
...
public MyViewHolder(View itemView) {
super(itemView);
}
}
}
RecyclerView is supposed to reuse the views. It will be slow if you throw away the already created TextView / ImageView objects and create new ones every time.
It sounds like you need a RecyclerView with multiple view types. The idea is to create multiple view holders - some of them with ImageView, the others with TextView. You'll have to override the getItemViewType(int position) method of your adapter - it should return different values for the IMAGE items and the TEXT items. The onCreateViewHolder(ViewGroup parent, int viewType) receives a viewType parameter so you know which type of ViewHolder to create there. In the onBindViewHolder(VH holder, int position) you could assume that the holder passed to you is the correct type (i.e. the type with TextView for TEXT items and the type with ImageView for IMAGE items), so there is no need to remove its child views and create them again.
There is nice article about RecyclerView's Adapters with multiple view types here.
i'm new to android,
I've been working on a project, and in my news feeds page, I'm trying to include a modular feed RecyclerView, which shows a question with different answer forms, varrying according to the Question type. The way I was doing it so far was by using the include and turning the forms visible when needed. recently since i added more modules, the app started to slowdown segnificantly, so i'm trying to implement ViewStubs.
This is my RecyclerView adapter:
public class ReQuestionAdapter extends RecyclerView.Adapter<FeedItem> {
private ArrayList<Question> myQuestions;
public ReQuestionAdapter(Context context, ArrayList<Question> questions) {
myQuestions = questions ;
}
#Override
public FeedItem onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext())
.inflate(R.layout.list_item_re_question, parent, false);
return new FeedItem(view);
}
#Override
public void onBindViewHolder(FeedItem holder, int position) {
Question q = myQuestions.get(position);
holder.bindQuestion(q);
}
#Override
public int getItemViewType(int position) {
return 0;
}
#Override
public int getItemCount() {
return myQuestions.size();
}
}
And this is the ViewHolder class for the adapter:
public class FeedItem extends RecyclerView.ViewHolder{
private Question mQuestion;
public TextView tvName;
public TextView tvTime;
public TextView tvContent;
public ProfilePictureView profilePictureView;
public ViewStub moduleView;
private int moduleType;
public FeedItem(View itemView) {
super(itemView);
}
public void bindQuestion(Question question) {
mQuestion = question;
tvTime = (TextView) itemView.findViewById(R.id.li_q_date);
tvContent = (TextView) itemView.findViewById(R.id.li_q_content);
moduleView = (ViewStub) itemView.findViewById(R.id.module_viewstub);
tvTime.setText(TimeHandler.When(mQuestion.publish_time));
tvContent.setText(mQuestion.content);
moduleType = question.type;
switch (moduleType) {
case Question.TYPE_YN:
moduleView.setLayoutResource(R.layout.module_yes_no);
moduleView.inflate();
break;
case Question.TYPE_CUSTOM:
moduleView.setLayoutResource(R.layout.module_custom);
moduleView.inflate();
break;
default:
break;
}
}
}
Now, the problem is that the ViewStub which contains a certain layout, cannot be reinflated with a new one, the reason for that is that it gets removed from the view hirarchy as soon as it leaves the screen, the symptoms:
When scrolling down the RecyclerView, the first list items that fill the screen are working perfect, but others to load when the previous leave the screen cause the FeedItem binding to bring a NullPointerException. (It canno't find it in the list item layout).
I'm looking for a solution as efficiant as ViewStubs, or a way to make them work properly, since I got many modules and inflating them all in each item as invisible would make my app slow.
In your bindQuestion() method you are referencing two different layouts to inflate, so in essence you have two different view types.
Adapter views have an efficient way way to handle this built right in.
Start by overriding getItemViewType(). When the item at position gets the module_yes_no layout, return 0. When it gets the module_custom layout, return 1.
Then in onCreateViewHolder(), when the viewType parameter is 0, inflate a list_item_re_question view complete with the module_yes_no layout. When viewType == 1, inflate the module_custom version of the view.
Now when you get a view in onBindViewHolder(), it will already have the correct subview, so you proceed to fill out that view as needed. By using getItemViewType(), the RecyclerView is working with you to recycle the exact view you need.
You can even have two FeedItem subclasses, one for module_yes_no and one for module_custom, so in onBindViewHolder(), you just check the class of the ViewHolder and branch accordingly.
That should help improve the performance of your app.
I'm using RecyclerView to create a list, and i was suffering a lot, because i saw different ways to implement an OnClickListener, and comments says like very coupled, very tricky, etc.
And about several days thinking how to implement it, i did this.
On my Fragment, implement the View.OnClickListener and the onClickEvent and when i'm implementing the RecyclerView.Adapter pass the View.OnClickListener reference in the constructor, like this:
public RecyclerViewRepoListAdapter(View.OnClickListener fragmentListener, List<Repos> repoList){
if (repoList != null){
this.reposList = repoList;
this.fragmentListener = fragmentListener;
}
}
After that, when i'm creating the Holder to the different list components, i register the Listener to every (in this case) LinearLayout like this:
#Override
public ListItemViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
//Inflate the corresponding layout
View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_repositories, parent, false);
//OnClickListener
itemView.setOnClickListener(fragmentListener);
//Here modify the view like margins, paddings, view size and layout parameters
//return the ViewHolder
return new ListItemViewHolder(itemView);
}
My cuestion is, what is your opinion about this implementation?
And if its ok, i hope this helps another one.