Develop Reference

ListView overlay another layout when scroll

Actually I don't know how it properly called - overlay, parallax or slideUP, whatever, I have an Activity called "cafe details" which presents a Container(LinearLayout) with header information (name, min price, delivery time min e.t.c) and other container (ViewPager) which contains a ExpandableListView with something information (menus&dishes) and all I want to do is slide up my Viewpager when scrolls listview to scpecific Y position to cover(or overlay) header information.
A similar effect (but with parallax that I don't need to use) looks like this
I can detect when user scrolling listview down or up but how I can move container with ViewPager to overlay other container? Please give me ideas, regards.
UPD
I have tried a huge number of ways how to implement it and all of them unfortunately are not suitable. So now I have come to next variant - add scroll listener to ListView, calculate scrollY position of view and then based on that move the viewpager on y axis by calling setTranslationY();
Here is some code
1) ViewPager's fragment
mListView.setOnScrollListener(new AbsListView.OnScrollListener() {
#Override
public void onScrollStateChanged(AbsListView absListView, int i) {
}
#Override
public void onScroll(AbsListView absListView, int i, int i1, int i2) {
if (getActivity() != null) {
((MainActivity) getActivity()).resizePagerContainer(absListView);
}
}
});
2) MainActivity
//object fields
int previousPos;
private float minTranslation;
private float minHeight;
<--------somewhere in onCreate
minTranslation = - (llVendorDescHeaders.getMeasuredHeight()+llVendorDescNote.getMeasuredHeight());
//llVendorDescHeaders is linearLayout with headers that should be hidden
//lVendorDescNote is a textView on green background;
minHeight = llVendorDescriptionPagerContainer.getMeasuredHeight();
//llVendorDescriptionPagerContainer is a container which contains ViewPager
--------->
public void resizePagerContainer(AbsListView absListView){
final int scrollY = getScrollY(absListView);
if (scrollY != previousPos) {
final float translationY = Math.max(-scrollY, minTranslation);
llVendorDescriptionPagerContainer.setTranslationY(translationY);
previousPos = scrollY;
}
}
private int getScrollY(AbsListView view) {
View child = view.getChildAt(0);
if (child == null) {
return 0;
}
int firstVisiblePosition = view.getFirstVisiblePosition();
int top = child.getTop();
return -top + firstVisiblePosition * child.getHeight() ;
}
This simple solution unfortunately has a problem - it is blinking and twitching (I don't know how to call it right) when scrolls slowly. So instead setTranslationY() I've used an objectAnimator:
public void resizePagerContainer(AbsListView absListView){
.............
ObjectAnimator moveAnim = ObjectAnimator.ofFloat(llVendorDescriptionPagerContainer, "translationY", translationY);
moveAnim.start();
..............
}
I don't like this solution because 1) anyway it does resize viewpager with delay, not instantly 2) I don't think that is good idea to create many ObjectAnimator's objects every time when I scroll my listView.
Need your help and fresh ideas. Regards.

I'm assuming that you are scrolling the top header (the ImageView is a child of the header) based on the scrollY of the ListView/ScrollView, as shown below:
float translationY = Math.max(-scrollY, mMinHeaderTranslation);
mHeader.setTranslationY(translationY);
mTopImage.setTranslationY(-translationY / 3); // For parallax effect
If you want to stick the header/image to a certain dimension and continue the scrolling without moving it anymore, then you can change the value of mMinHeaderTranslation to achieve that effect.
//change this value to increase the dimension of header stuck on the top
int tabHeight = getResources().getDimensionPixelSize(R.dimen.tab_height);
mHeaderHeight = getResources().getDimensionPixelSize(R.dimen.header_height);
mMinHeaderTranslation = -mHeaderHeight + tabHeight;
The code snippets above are in reference to my demo but I think it's still general enough for you.
If you're interested you can check out my demo
https://github.com/boxme/ParallaxHeaderViewPager

Have you tried CoordinatorLayout from this new android's design support library? It looks like it's what you need. Check this video from 3:40 or this blog post.

change the Listview dimensions dynamically with respect to the phone screen

How can change the position of the list view dynamically.For example my list view initially covers 2/4 of the screen and on scroll down ,I want the list will size to expand and cove 3/4 of the screen.
below code is giving me whether user is scrolling up or down in the list view
#Override
public void onScroll(AbsListView view, int firstVisibleItem,int visibleItemCount, int totalItemCount) {
final ListView lw = lv;
if (view.getId() == lw.getId()) {
final int currentFirstVisibleItem = lw.getFirstVisiblePosition();
if (currentFirstVisibleItem > mLastFirstVisibleItem) {
mIsScrollingUp = false;
}
else if (currentFirstVisibleItem < mLastFirstVisibleItem) {
mIsScrollingUp = true;
}
mLastFirstVisibleItem = currentFirstVisibleItem;
}
}
thanks in advance

The idea is to use a layout (a LinearLayout or RelativeLayout) and a transparent view whose visibility may change to GONE.
Something like:
<LinearLayout ...>
<ListView android:layout_height="0px" android:layout_weight="1" .../>
<View android:background="#null" android:layout_weight="0.5" android:visibility="gone" ...>
<View android:background="#null" android:layout_weight="0.5" android:visibility="visible" ...>
</LinearLayout>
If you change the visibility of the 2nd layout item from gone to visible, the ListView will change its height from 2/3 to 1/2 of the LinearLayout height.
Disclaimer: I myself find the idea of changing the ListView height very counter-intuitive.
Just in case: View.getMeasuredHeight() gives the real height but you may have to define a ViewTreeObserver.OnGlobalLayoutListener to get notified when it becomes calculated. When you react on input events, the measured height is already calculated.

That is achieved by using DisplayManager class. Sorry I haven't tested the following code, but it should work, although you might need to fix some errors and constraints, the logic is fine:
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
Display mainDisplay = ((DisplayManager)Context.getSystemService(DISPLAY_SERVICE)).getDisplay(0);
Point screenSize = new Point();
mainDisplay.getSize(screenSize);
view.setLayoutParams(new LayoutParams(screenSize.x * 3 / 4, screenSize.y * 3 / 4));
//rest of your code
}
However, the problem you'll be facing afterwards is that your ListView won't revert back once you stop scrolling, you need to create an additional method (and Event handler) that would accomplish that.

how to display footer view to the end of the screen in the case when the list has very few items?

I want to add a footer to the listview. When the number of list items are more,the footer works fine.
But when listview has very few items,the footer gets displayed in the middle of the screen,just below the listview .which looks shabby.In such case i want the footer to align parent bottom.
Thankyou in anticipation.

it is a simplest example of what you want. you can customize it:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/RelativeLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ListView
android:id="#+id/listView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="#+id/footer"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true" >
</ListView>
<RelativeLayout
android:layout_width="wrap_content"
android:layout_height="90dp"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_alignParentRight="true"
android:id="#+id/footer" >
</RelativeLayout>
</RelativeLayout>
if you want do that you said in comment you must set layout param's of footer in code, you must get the size of your list, then get the number of row that shows in screen, then
if (listSize < numRow)
//set footer to bottom of your list
else
// android:layout_alignParentBottom="true"

Maybe your listview's height is set to wrap_content?
As far as I know the footer is added at the bottom of the listview. If you set the listview's height to match_parent it should be aligned to the bottom and also the footer should be displayed there.
(If you use a relative layout simply set listview's attribute alignParentBottom="true" in your .xml file)

You can use RecyclerView with RecyclerView.ItemDecoration to implement this behavior.
public class StickyFooterItemDecoration extends RecyclerView.ItemDecoration {
/**
* Top offset to completely hide footer from the screen and therefore avoid noticeable blink during changing position of the footer.
*/
private static final int OFF_SCREEN_OFFSET = 5000;
#Override
public void getItemOffsets(Rect outRect, final View view, final RecyclerView parent, RecyclerView.State state) {
int adapterItemCount = parent.getAdapter().getItemCount();
if (isFooter(parent, view, adapterItemCount)) {
//For the first time, each view doesn't contain any parameters related to its size,
//hence we can't calculate the appropriate offset.
//In this case, set a big top offset and notify adapter to update footer one more time.
//Also, we shouldn't do it if footer became visible after scrolling.
if (view.getHeight() == 0 && state.didStructureChange()) {
hideFooterAndUpdate(outRect, view, parent);
} else {
outRect.set(0, calculateTopOffset(parent, view, adapterItemCount), 0, 0);
}
}
}
private void hideFooterAndUpdate(Rect outRect, final View footerView, final RecyclerView parent) {
outRect.set(0, OFF_SCREEN_OFFSET, 0, 0);
footerView.post(new Runnable() {
#Override
public void run() {
parent.getAdapter().notifyDataSetChanged();
}
});
}
private int calculateTopOffset(RecyclerView parent, View footerView, int itemCount) {
int topOffset = parent.getHeight() - visibleChildsHeightWithFooter(parent, footerView, itemCount);
return topOffset < 0 ? 0 : topOffset;
}
private int visibleChildsHeightWithFooter(RecyclerView parent, View footerView, int itemCount) {
int totalHeight = 0;
//In the case of dynamic content when adding or removing are possible itemCount from the adapter is reliable,
//but when the screen can fit fewer items than in adapter, getChildCount() from RecyclerView should be used.
int onScreenItemCount = Math.min(parent.getChildCount(), itemCount);
for (int i = 0; i < onScreenItemCount - 1; i++) {
totalHeight += parent.getChildAt(i).getHeight();
}
return totalHeight + footerView.getHeight();
}
private boolean isFooter(RecyclerView parent, View view, int itemCount) {
return parent.getChildAdapterPosition(view) == itemCount - 1;
}
}
Make sure to set match_parent for the RecyclerView height.
Please have a look at the sample application https://github.com/JohnKuper/recyclerview-sticky-footer and how it works http://sendvid.com/nbpj0806
A Huge drawback of this solution is it works correctly only after notifyDataSetChanged() throughout an application(not inside decoration). With more specific notifications it won't work properly and to support them, it requires a way more logic. Also, you can get insights from the library recyclerview-stickyheaders by eowise and improve this solution.

Android ListView: Can not center items on start up, due to Null Pointer Exception

This is my first ever post here and I'm a dumb novice, so I hope someone out there can both help me and excuse my ignorance.
I have a ListView which is populated with an ArrayAdapter. When I either scroll or click, I want the selected item, or the item nearest the vertical center, to be forced to the exact vertical center of the screen. If I call listView.setSelection(int position) it aligns the selected position at the top of the screen, so I need to use listView.setSelectionFromTop(position, offset) instead. To find my offset, I take half of the View's height from the half of the ListView's height.
So, I can vertically center my item easy enough, within OnItemClick or OnScrollStateChanged, with the following:
int x = listView.getHeight();
int y = listView.getChildAt(0).getHeight();
listView.setSelectionFromTop(myPosition, x/2 - y/2);
All this works fine. My problem is with the initial ListView setup. I want an item to be centered when the activity starts, but I can't because I get a NullPointerException from:
int y = listView.getChildAt(0).getHeight();
I understand this is because the ListView has not yet rendered, so it has no children, when I call this from OnCreate() or OnResume().
So my question is simply: how can I force my ListView to render at startup so I can get the height value I need? Or, alternatively, is there any other way to center items vertically within a ListView?
Thanks in advance for any help!

int y = listView.getChildAt(0).getHeight();
I understand this is because the ListView has not yet rendered, so it has no children, when I call this from onCreate() or onResume().
You should call it in onScroll.
listView.setOnScrollListener(new OnScrollListener() {
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
}
#Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
//Write your logic here
int y = listView.getChildAt(0).getHeight();
}
});

I'm answering my own question here, but it's very much a hack. I think it's interesting because it sheds some light on the behavior of listviews.
The problem was in trying to act on data (a listview row) that did not yet exist (it had not been rendered). listview.getChildAt(int) was null because the listview had no children yet. I found out onScroll() is called immediately when the activity is created, so I simply put everything in a thread and delayed the getChildAt() call. I then enclosed the whole thing in a boolean wrapper to make sure it is only ever called once (on startup).
The interesting thing was that I only had to delay the call by 1ms for everything to be OK. And that's too fast for the eye to see.
Like I said, this is all a hack so I'm sure all this is a bad idea. Thanks for any help!
private boolean listViewReady = false;
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
if (!listViewReady){
Thread timer = new Thread() {
public void run() {
try{
sleep(1);
}catch (InterruptedException e) {
e.printStackTrace();
}finally{
runOnUiThread(new Runnable() {
public void run() {
myPosition = 2;
int x = listView.getHeight();
int y = listView.getChildAt(0).getHeight();
listView.setSelectionFromTop(myPosition, x/2 - y/2);
listViewReady = true;
}
});
}
}
};
timer.start();
}//if !ListViewReady

I have achieved the same using a in my opinion slighlty simpler solution
mListView.post(new Runnable() {
#Override
public void run() {
int height = mListView.getHeight();
int itemHeight = mListView.getChildAt(0).getHeight();
if (positionOfMyItem == myCollection.size() - 1) {
// last element - > don't subtract item height
itemHeight = 0;
}
mListView.setSelectionFromTop(position, height / 2 - itemHeight / 2);
}
});

List view snap to item

I'm creating a list of pictures using a ListView and the photos are of a size that would fit 2 to 3 photos on the screen.
The problem that I'm having is that I would like to when the user stops scrolling that the first item of the visible list would snap to the top of screen, for example, if the scroll ends and small part of the first picture displayed, we scroll the list down so the picture is always fully displayed, if mostly of the picture is displayed, we scroll the list up so the next picture is fully visible.
Is there a way to achieve this in android with the listview?

I've found a way to do this just listening to scroll and change the position when the scroll ended by implementing ListView.OnScrollListener
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
switch (scrollState) {
case OnScrollListener.SCROLL_STATE_IDLE:
if (scrolling){
// get first visible item
View itemView = view.getChildAt(0);
int top = Math.abs(itemView.getTop()); // top is a negative value
int bottom = Math.abs(itemView.getBottom());
if (top >= bottom){
((ListView)view).setSelectionFromTop(view.getFirstVisiblePosition()+1, 0);
} else {
((ListView)view).setSelectionFromTop(view.getFirstVisiblePosition(), 0);
}
}
scrolling = false;
break;
case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
case OnScrollListener.SCROLL_STATE_FLING:
Log.i("TEST", "SCROLLING");
scrolling = true;
break;
}
}
The change is not so smooth but it works.

Utilizing a couple ideas from #nininho's solution, I got my listview to snap to the item with a smooth scroll instead of abruptly going to it. One caveat is that I've only tested this solution on a Moto X in a basic ListView with text, but it works very well on the device. Nevertheless, I'm confident about this solution, and encourage you to provide feedback.
listview.setOnScrollListener(new OnScrollListener() {
#Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// TODO Auto-generated method stub
if (scrollState == SCROLL_STATE_IDLE) {
View itemView = view.getChildAt(0);
int top = Math.abs(itemView.getTop());
int bottom = Math.abs(itemView.getBottom());
int scrollBy = top >= bottom ? bottom : -top;
if (scrollBy == 0) {
return;
}
smoothScrollDeferred(scrollBy, (ListView)view);
}
}
private void smoothScrollDeferred(final int scrollByF,
final ListView viewF) {
final Handler h = new Handler();
h.post(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
viewF.smoothScrollBy(scrollByF, 200);
}
});
}
#Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
// TODO Auto-generated method stub
}
});
The reason I defer the smooth scrolling is because in my testing, directly calling the smoothScrollBy method in the state changed callback had problems actually scrolling. Also, I don't foresee a fully-tested, robust solution holding very much state, and in my solution below, I hold no state at all. This solution is not yet in the Google Play Store, but should serve as a good starting point.

Using #nininho 's solution,
In the onScrollStateChanged when the state changes to SCROLL_STATE_IDLE, remember the position to snap and raise a flag:
snapTo = view.getFirstVisiblePosition();
shouldSnap = true;
Then, override the computeScroll() method:
#Override
public void computeScroll() {
super.computeScroll();
if(shouldSnap){
this.smoothScrollToPositionFromTop(snapTo, 0);
shouldSnap = false;
}
}

You can do a much more smooth scrolling if you use RecyclerView. The OnScrollListener is way better.
I have made an example here: https://github.com/plattysoft/SnappingList

Well.. I know 10 years have past since this question was asked, but now we can use LinearSnapHelper:
new LinearSnapHelper().attachToRecyclerView(recyclerView);
Source:
https://proandroiddev.com/android-recyclerview-snaphelper-19eaa9598da6

Apart from trying the code above one thing you should make sure of is that your listView have a height that can fit exact number of items you want to be displayed.
e.g
If you want 4 items to be displayed after snap effect and your row height (defined in its layout) should be 1/4 of the total height of the list.

Note that after the smoothScrollBy() call, getFirstVisiblePosition() may point to the list item ABOVE the topmost one in the listview. This is especially true when view.getChildAt(0).getBottom() == 0. I had to call view.setSelection(view.getFirstVisiblePosition() + 1) to remedy this odd behavior.