Develop Reference

RecyclerView Adapter - Where can you access item view after Layout?

onBindViewHolder
Is a nice method but there is one problem - The View has not necessarily been measured yet. So where can I adjust things like amount of content in TextView's etc if I cannot get the actual measurements on the View? I want to change dynamically change the length of Strings rendered in the Item view if the ItemView is a certain width in comparison to the string length. I have measured the CharSet length etc. No problem, but how do I know if it is too long if I cannot measure the width of the View? with the items played out. The String can also be between two items etc. So I need to at least know where I can access this kind of information. Thanks.

You can add a listener to listen for changes in the view tree and get the view's width and height after it has finished measurement.
final ViewTreeObserver obs = mTextView.getViewTreeObserver();
obs.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
#Override
public boolean onPreDraw () {
int height = mTextView.getHeight();
int width = mTextView.getWidth();
// Return true to proceed with the current drawing pass, or false to cancel.
return true;
}
});

How to get the height of recyclerview item in "onBindViewHolder"

The height of RecyclerView item is not fixed,i need to set the background image for every item,so I want to get the height of recyclerview's item to resize the Image,but the itemView.getHeight() always return 0 in onBindViewHolder.
I have try to search many questions or articles,but i still cant get a good soluation.

Short
Measure the View manually
view.measure(
View.MeasureSpec.makeMeasureSpec(recyclerViewWidth, View.MeasureSpec.EXACTLY),
View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
and get the height with view.getMeasuredHeight()
Background
A view will return a valid value for View.getHeight()only after it has been measured. The measuring itself will automatically happen by the system when the view is about to be displayed on screen.
When Android wants to display the layout, it will recursively call the view.layout() function for each view in the view tree. Each Parent tells its children the constraints they might have (width/height) and ask them to view.measure() themselves. As a result, the view will store the measured values BASED on the constraints in designated members (MeasuredHeight/Width). Note that at this point view.getMeasuredHeight() will hold the value while view.getHeight() will still be invalid. view.getHeight() will only return a valid value once the view has an actual height in the UI hierarchy.
Recap
So, to know the height of a view element, before it has been measured and laid out by the system, we will need to invoke the view.measure() function manually.
The measure function expects 2 parameters which derived from the view LayoutParams + the parent constraints.
In the above code sample, we are measuring the view forcing its width to be EXACTLY the width of the parent (the RecycleView), and the height is not limited.

I suggest that you define multiple layout files with the expected heights and inflate them according to some criteria in your data set.
ViewHolder onCreateViewHolder (ViewGroup parent, int viewType){
if(some condition){
//inflate layout 1
}else{
//inflate layout 2
}
or as answered here: you can get the measurements while initializing the view holder
itemView.measure(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED);
int width = itemView.getMeasuredWidth();
int height = itemView.getMeasuredHeight();

How about this:
view.post(() -> {
int width = view.getMeasuredWidth();
int height = view.getMeasuredHeight();
}

using this code to get recycler view's item height:
view.getViewTreeObserver().addOnGlobalLayoutListener(new
ViewTreeObserver.OnGlobalLayoutListener() {
#Override
public void onGlobalLayout() {
//don't forget remove this listener
view.getViewTreeObserver().removeOnGlobalLayoutListener(this);
//get item height here
int itemHeight = v.getHeight();
}
});

MyViewHolder.kt
With the addOnGlobalLayoutListener() method, the height value is obtained before the TextView is drawn. And then save it in a member variable.
The key is to modify the UI inside and outside the implementation of the listener so that there are no rendering problems (when the views are redrawn).
That is, you shoud use the getter inside the listener and; the setter inside and outside the listener.
companion object {
var maxHeight: Int = 0
fun create(mContext: Context): MyViewHolder {
val view = LayoutInflater.from(mContext).inflate(R.layout.item_answer, null)
updateLayout(view)
view.viewTreeObserver.addOnGlobalLayoutListener {
if (view.myTextView.height > maxHeight)
maxHeight = view.myTextView.height
updateLayout(view)
}
return MyViewHolder(mContext, view).apply {
setIsRecyclable(false)
}
}
fun updateLayout(view: View) {
if (maxHeight != 0 && view.myTextView.height != maxHeight)
view.myTextView.height = maxHeight
}
}
Source

How to determine column position in staggered grid layout manager

I’m using a staggered recycler view layout for a list of photos. I want the spacing on the sides to be zero while still having space between the two columns. I’m using an item decoration sub class to get the spacing seen in the attached photo. I know I have control over the left and right spacing but the problem is that I never know which column the photo is in. It seems like the staggered layout manager does some of its own reordering. I've tried using getChildAdapterPosition but it seems to return the position in the data source array and not the actual position of the photo in the layout. Any idea how I should approach this?

I managed to get it working. In my case, I don't need any borders on the left or right edges of the screen. I just need borders in the middle and bottom. The solution is to get the layout parameters of the view that are of type StaggeredGridLayoutManager.LayoutParams. In those parameters you can get the spanIndex that tells you on which index the view is. So if you have a spanCount of 2, the left view will have a spanIndex of 0 and the right view will have a spanIndex of 1.
Here is my code, maybe it help you.
public class SpaceItemDecoration extends RecyclerView.ItemDecoration {
private int space;
public SpaceItemDecoration(int space) {
this.space = space;
}
#Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
int position = parent.getChildAdapterPosition(view);
StaggeredGridLayoutManager.LayoutParams lp = (StaggeredGridLayoutManager.LayoutParams) view.getLayoutParams();
int spanIndex = lp.getSpanIndex();
if (position > 0) {
if (spanIndex == 1) {
outRect.left = space;
} else {
outRect.right = space;
}
outRect.bottom = space * 2;
}
}
}
In my case, firstly I have to get the position, since on the index 0 I have a header View, which doesn't have any borders. After that, I get the span index and depending on it I set the borders that I need on that View. And finally I set the bottom border on every View.

so the one solution I was able to use was with an item decorator but it definitely is a little weird/hacky feeling.
Basically you'll adjust the outer rectangle of the item based on its column position (or something similar). My understanding is that the outer rectangle is more or less the spacing you want to change. Give the code below a try, obviously you'll need to make your own adjustments and logic to 'calculate' which column the item is on but this should be enough to figure it out, hopefully:
recyclerView.addItemDecoration(new RecyclerView.ItemDecoration() {
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
int left = outRect.left;
int right = outRect.right;
int top = outRect.top;
int bottom = outRect.bottom;
int idx = parent.getChildPosition(view);
int perRow = gridLayoutManager.getSpanCount();
int adj = blahh... // some adjustment
if (idx < itemsPerRow) {
// on first row, adjust top if needed
}
if(idx % perRow == 0){
// on first column, adjust. Left magically adjusts bottom, so adjust it too...
left += adj;
bottom -= adj;
}
if(idx % itemsPerRow == perRow - 1){
// on last column, adjust. Right magically adjusts bottom, so adjust it too...
right += adjustment;
bottom -= adjustment;
}
outRect.set(left, top, right, bottom);
}
});
Again this is hacky and takes some trial and error to get right.
Another solution I have tried with some success is to define different views for the different columns. In your case the columns would have views with different, negative margins, on the left and right to get the effect you want.
As a side note, I assume you are using an elevation on the card view. One thing I've noticed is that if the card view does NOT have elevation and instead you handle it yourself (yeah, i know, isn't the point to not handle elevation yourself) much of this difficulty goes away and things start to behave, likely because of the elevation/shadow calculations. But anyway... Hope this is at least somewhat helpful...

Android - StaggeredGrid wrong items disposition

I have a problem with my Recycler view and StaggeredGrid which cut the width by 2.
I load images into items with Picasso and when I load image first time, they are disposed strangely in the recycler view.
After reloading, everything seems good.
I think problem come from image loading : the StaggeredGrid doesn't know the image height the first time, but know after reloading because of cache.
How can i solve this problem ?

I think you have answered your own question. You need to load the images/determine their dimensions before adding the data to the recycler.

Solved by changing gap strategy to :
StaggeredGridLayoutManager manager = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
manager.setGapStrategy(StaggeredGridLayoutManager.GAP_HANDLING_MOVE_ITEMS_BETWEEN_SPANS);
recyclerView.setLayoutManager(manager);
Change the position of items automatically

This happens because the holder dose not recognize the width and height of the Image view when you scroll up and down. It clears the upper view when you scroll down and vice versa.
Use like this :
#Override
public void onBindViewHolder(ViewHolder viewHolder, int position) {
MyViewHolder vh = (MyViewHolder) viewHolder;
ImageModel item = imageModels.get(position);
RelativeLayout.LayoutParams rlp = (RelativeLayout.LayoutParams)vh.imageView.getLayoutParams();
float ratio = item.getHeight() / item.getWidth();
rlp.height = (int) (rlp.width * ratio);
vh.imageView.setLayoutParams(rlp);
vh.positionTextView.setText("pos: " + position);
vh.imageView.setRatio(item.getRatio());
Picasso.with(mContext).load(item.getUrl()).placeholder(PlaceHolderDrawableHelper.getBackgroundDrawable(position)).into(vh.imageView);
}
For clear see this link: Picasso/Glide-RecyclerView-StaggeredGridLayoutManager

Android List view fill the height to the contents

i have a list view defined in the xml, now i am setting the content view setContentView(R.layout.topic_layout); , i have 5 items in it,currently its filling only half the height of the list view but i want it to completely fill the height so that i dont have any space at the bottom.
i have searched for it but couldnt find any solution, please help me to acheive this :
and also i am setting the adapter like this:
adapter = new MyAdapter(this);
if (adapter != null) {
setListAdapter(adapter);
}

If you have a fixed number of items and want them to stretch all the way to the end of the screen, ListView is not the best choice for you. Use a LinearLayout which takes up all the space and add all the items to it. This is assuming you want the items to take up all the space every time.
Using LinearLayout, you can spread the items out evenly without doing any calculations yourself.
LinearLayout linearLayout = new LinearLayout(getSupportActivity());
linearLayout.setOrientation(android.widget.LinearLayout.VERTICAL);
RelativeLayout.LayoutParams params = new LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
ViewGroup.LayoutParams.MATCH_PARENT);
for (int i = 0; i < 5; i++) {
View individualView = new View(getSupportActivity());
// Create your custom view here and add it to the linear layout
// Leave the height as 0, LinearLayout will calculate the height properly.
params = new LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, 0);
additionalOption.setLayoutParams(params);
// As a we are adding it to the linear layout, they will all have a weight of 1, which will make them spread out evenly.
linearLayout.addView(additionalOption);
}
mainView.addView(linearLayout);
EDIT: If you have already implemented it with ListView and is troublesome to change it, you can do the following.
Make sure the list view width and height are set to match_parent in the xml. Then in getView() of the adapter where you create your custom view, do the following
// Get the height of the ListView
int totalHeight = listView.getHeight();
int rowHeight = totalHeight/getCount(); // Divide by number of items.
// Create custom view with the height calculated above.
Be careful about the totalHeight being 0. If you create the ListView in onCreate() and set the adapter in onCreate() as well, the ListView will most likely not have the width or height calculated yet. Try setting the adapter in onResume() instead. By this point, the dimensions of the ListView would have been calculated and laid out on the screen.
Hope this helps.

I totally agree with #Aswin, using LinearLayout with layout_weight property would be your solution. But if you insist to use listView, i can offer you a workout which is not so recommended.
You can get your screenHeight when activity created by using these codes:
Display display = ((WindowManager) getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();
DisplayMetrics dm = new DisplayMetrics();
display.getMetrics(dm);
int height = dm.heightPixels;
int listItemHeight = height / YOUR_ITEM_COUNT;
Then you can use this listItemHeight in your listAdapter, by setting inflated view's height on getView method.

This is what I use to do:
Set your xml listview height to match_parent instead of wrap_content, in order to fill all the available space.
Set the minimum height of each item in the listview to match the listview height divided by the number of elements.
Activity Layout:
(...)
<ListView
android:id="#+id/myListView"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
(...)
ArrayAdapter for the Listview:
private class MyAdapter extends ArrayAdapter<MyObject> {
(...)
#Override
public View getView(int position, View convertView, ViewGroup parent) {
MyObject myobject = getItem(position);
ObjectHolder oh;
if (convertView == null) {
LayoutInflater mInflater = (LayoutInflater) myContext.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
convertView = mInflater.inflate(R.layout.myitemlayout, parent, false);
// This is the important line:
convertView.setMinimumHeight(parent.getHeight()/getCount());
(...)
return convertView;
}
}