问题
I have the following requirement:
- At first, data for page no: 2 is fetched from the server & the items are populated in a ListView.
Considering that both the prev page & next page are available in a scenario, the following code has been added:
if(prevPageNo > 0){
mListViewActual.setOnScrollListener(this);
}
if(nextPageNo > 0){
mListViewActual.setOnScrollListener(this);
}
What conditions should I put to detect scroll up & scroll down on the following methods:
- void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)
- void onScrollStateChanged(AbsListView view, int scrollState)
After the action: scroll up & scroll down is detected , accordingly a service will be called with either the prev page no or next page no , to fetch the items to be populated in the Listview.
Any inputs will be helpful.
Gone through the following links but its not returning the correct scroll up / scroll down action:
link 1 link 2
回答1:
try using the setOnScrollListener and implement the onScrollStateChanged with scrollState
setOnScrollListener(new OnScrollListener(){
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
// TODO Auto-generated method stub
}
public void onScrollStateChanged(AbsListView view, int scrollState) {
// TODO Auto-generated method stub
final ListView lw = getListView();
if(scrollState == 0)
Log.i("a", "scrolling stopped...");
if (view.getId() == lw.getId()) {
final int currentFirstVisibleItem = lw.getFirstVisiblePosition();
if (currentFirstVisibleItem > mLastFirstVisibleItem) {
mIsScrollingUp = false;
Log.i("a", "scrolling down...");
} else if (currentFirstVisibleItem < mLastFirstVisibleItem) {
mIsScrollingUp = true;
Log.i("a", "scrolling up...");
}
mLastFirstVisibleItem = currentFirstVisibleItem;
}
}
});
回答2:
Here is a working modified version from some of the above-indicated solutions.
Add another class ListView:
package com.example.view;
import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.widget.AbsListView;
public class ListView extends android.widget.ListView {
private OnScrollListener onScrollListener;
private OnDetectScrollListener onDetectScrollListener;
public ListView(Context context) {
super(context);
onCreate(context, null, null);
}
public ListView(Context context, AttributeSet attrs) {
super(context, attrs);
onCreate(context, attrs, null);
}
public ListView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
onCreate(context, attrs, defStyle);
}
@SuppressWarnings("UnusedParameters")
private void onCreate(Context context, AttributeSet attrs, Integer defStyle) {
setListeners();
}
private void setListeners() {
super.setOnScrollListener(new OnScrollListener() {
private int oldTop;
private int oldFirstVisibleItem;
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
if (onScrollListener != null) {
onScrollListener.onScrollStateChanged(view, scrollState);
}
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
if (onScrollListener != null) {
onScrollListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
}
if (onDetectScrollListener != null) {
onDetectedListScroll(view, firstVisibleItem);
}
}
private void onDetectedListScroll(AbsListView absListView, int firstVisibleItem) {
View view = absListView.getChildAt(0);
int top = (view == null) ? 0 : view.getTop();
if (firstVisibleItem == oldFirstVisibleItem) {
if (top > oldTop) {
onDetectScrollListener.onUpScrolling();
} else if (top < oldTop) {
onDetectScrollListener.onDownScrolling();
}
} else {
if (firstVisibleItem < oldFirstVisibleItem) {
onDetectScrollListener.onUpScrolling();
} else {
onDetectScrollListener.onDownScrolling();
}
}
oldTop = top;
oldFirstVisibleItem = firstVisibleItem;
}
});
}
@Override
public void setOnScrollListener(OnScrollListener onScrollListener) {
this.onScrollListener = onScrollListener;
}
public void setOnDetectScrollListener(OnDetectScrollListener onDetectScrollListener) {
this.onDetectScrollListener = onDetectScrollListener;
}
}
And an interface:
public interface OnDetectScrollListener {
void onUpScrolling();
void onDownScrolling();
}
And finally how to use:
com.example.view.ListView listView = (com.example.view.ListView) findViewById(R.id.list);
listView.setOnDetectScrollListener(new OnDetectScrollListener() {
@Override
public void onUpScrolling() {
/* do something */
}
@Override
public void onDownScrolling() {
/* do something */
}
});
In your XML layout:
<com.example.view.ListView
android:id="@+id/list"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
This is my first topic, do not judge me harshly. =)
回答3:
this is a simple implementation:
lv.setOnScrollListener(new OnScrollListener() {
private int mLastFirstVisibleItem;
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
if(mLastFirstVisibleItem<firstVisibleItem)
{
Log.i("SCROLLING DOWN","TRUE");
}
if(mLastFirstVisibleItem>firstVisibleItem)
{
Log.i("SCROLLING UP","TRUE");
}
mLastFirstVisibleItem=firstVisibleItem;
}
});
and if you need more precision, you can use this custom ListView class:
import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.widget.AbsListView;
import android.widget.ListView;
/**
* Created by root on 26/05/15.
*/
public class ScrollInterfacedListView extends ListView {
private OnScrollListener onScrollListener;
private OnDetectScrollListener onDetectScrollListener;
public ScrollInterfacedListView(Context context) {
super(context);
onCreate(context, null, null);
}
public ScrollInterfacedListView(Context context, AttributeSet attrs) {
super(context, attrs);
onCreate(context, attrs, null);
}
public ScrollInterfacedListView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
onCreate(context, attrs, defStyle);
}
@SuppressWarnings("UnusedParameters")
private void onCreate(Context context, AttributeSet attrs, Integer defStyle) {
setListeners();
}
private void setListeners() {
super.setOnScrollListener(new OnScrollListener() {
private int oldTop;
private int oldFirstVisibleItem;
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
if (onScrollListener != null) {
onScrollListener.onScrollStateChanged(view, scrollState);
}
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
if (onScrollListener != null) {
onScrollListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
}
if (onDetectScrollListener != null) {
onDetectedListScroll(view, firstVisibleItem);
}
}
private void onDetectedListScroll(AbsListView absListView, int firstVisibleItem) {
View view = absListView.getChildAt(0);
int top = (view == null) ? 0 : view.getTop();
if (firstVisibleItem == oldFirstVisibleItem) {
if (top > oldTop) {
onDetectScrollListener.onUpScrolling();
} else if (top < oldTop) {
onDetectScrollListener.onDownScrolling();
}
} else {
if (firstVisibleItem < oldFirstVisibleItem) {
onDetectScrollListener.onUpScrolling();
} else {
onDetectScrollListener.onDownScrolling();
}
}
oldTop = top;
oldFirstVisibleItem = firstVisibleItem;
}
});
}
@Override
public void setOnScrollListener(OnScrollListener onScrollListener) {
this.onScrollListener = onScrollListener;
}
public void setOnDetectScrollListener(OnDetectScrollListener onDetectScrollListener) {
this.onDetectScrollListener = onDetectScrollListener;
}
public interface OnDetectScrollListener {
void onUpScrolling();
void onDownScrolling();
}
}
an example for use: (don't forget to add it as an Xml Tag in your layout.xml)
scrollInterfacedListView.setOnDetectScrollListener(new ScrollInterfacedListView.OnDetectScrollListener() {
@Override
public void onUpScrolling() {
//Do your thing
}
@Override
public void onDownScrolling() {
//Do your thing
}
});
回答4:
ListView listView = getListView();
listView.setOnScrollListener(new OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
view.setOnTouchListener(new OnTouchListener() {
private float mInitialX;
private float mInitialY;
@Override
public boolean onTouch(View v, MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mInitialX = event.getX();
mInitialY = event.getY();
return true;
case MotionEvent.ACTION_MOVE:
final float x = event.getX();
final float y = event.getY();
final float yDiff = y - mInitialY;
if (yDiff > 0.0) {
Log.d(tag, "SCROLL DOWN");
scrollDown = true;
break;
} else if (yDiff < 0.0) {
Log.d(tag, "SCROLL up");
scrollDown = true;
break;
}
break;
}
return false;
}
});
回答5:
With all the method posted, there are problems recognizing when the user is scrolling up from the first element or down from the last. Here is another approach to detect scroll up/down:
listView.setOnTouchListener(new View.OnTouchListener() {
float height;
@Override
public boolean onTouch(View v, MotionEvent event) {
int action = event.getAction();
float height = event.getY();
if(action == MotionEvent.ACTION_DOWN){
this.height = height;
}else if(action == MotionEvent.ACTION_UP){
if(this.height < height){
Log.v(TAG, "Scrolled up");
}else if(this.height > height){
Log.v(TAG, "Scrolled down");
}
}
return false;
}
});
回答6:
My solution works perfectly giving the exact value for each scroll direction.
distanceFromFirstCellToTop contains the exact distance from the first cell to the top of the parent View. I save this value in previousDistanceFromFirstCellToTop and as I scroll I compare it with the new value. If it's lower then I scrolled up, else, I scrolled down.
private int previousDistanceFromFirstCellToTop;
listview.setOnScrollListener(new OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
View firstCell = listview.getChildAt(0);
int distanceFromFirstCellToTop = listview.getFirstVisiblePosition() * firstCell.getHeight() - firstCell.getTop();
if(distanceFromFirstCellToTop < previousDistanceFromFirstCellToTop)
{
//Scroll Up
}
else if(distanceFromFirstCellToTop > previousDistanceFromFirstCellToTop)
{
//Scroll Down
}
previousDistanceFromFirstCellToTop = distanceFromFirstCellToTop;
}
});
For Xamarin developers, the solution is the following:
Note: don't forget to run on UI thread
listView.Scroll += (o, e) =>
{
View firstCell = listView.GetChildAt(0);
int distanceFromFirstCellToTop = listView.FirstVisiblePosition * firstCell.Height - firstCell.Top;
if (distanceFromFirstCellToTop < previousDistanceFromFirstCellToTop)
{
//Scroll Up
}
else if (distanceFromFirstCellToTop > previousDistanceFromFirstCellToTop)
{
//Scroll Down
}
previousDistanceFromFirstCellToTop = distanceFromFirstCellToTop;
};
回答7:
I've used this much simpler solution:
setOnScrollListener( new OnScrollListener()
{
private int mInitialScroll = 0;
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount)
{
int scrolledOffset = computeVerticalScrollOffset();
boolean scrollUp = scrolledOffset > mInitialScroll;
mInitialScroll = scrolledOffset;
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
}
}
回答8:
To also detect scrolling with larger elements, I prefere an onTouch Listener:
listview.setOnTouchListener(new View.OnTouchListener() {
int scrollEventListSize = 5;
float lastY;
// Used to correct for occasions when user scrolls down(/up) but the onTouchListener detects it incorrectly. We will store detected up-/down-scrolls with -1/1 in this list and evaluate later which occured more often
List<Integer> downScrolledEventsHappened;
@Override
public boolean onTouch(View v, MotionEvent event) {
float diff = 0;
if(event.getAction() == event.ACTION_DOWN){
lastY = event.getY();
downScrolledEventsHappened = new LinkedList<Integer>();
}
else if(event.getAction() == event.ACTION_MOVE){
diff = event.getY() - lastY;
lastY = event.getY();
if(diff>0)
downScrolledEventsHappened.add(1);
else
downScrolledEventsHappened.add(-1);
//List needs to be filled with some events, will happen very quickly
if(downScrolledEventsHappened.size() == scrollEventListSize+1){
downScrolledEventsHappened.remove(0);
int res=0;
for(int i=0; i<downScrolledEventsHappened.size(); i++){
res+=downScrolledEventsHappened.get(i);
}
if (res > 0)
Log.i("INFO", "Scrolled up");
else
Log.i("INFO", "Scrolled down");
}
}
return false; // don't interrupt the event-chain
}
});
回答9:
Store the firstVisibleItem and on the next onScroll check if the new firstVisibleItem is smaller or greater than the previous one.
Example pseudocode (not tested):
int lastVisibleItem = 0;
boolean isScrollingDown = false;
void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
if (firstVisibleItem > lastVisibleItem) {
isScrollingDown = true;
}
else {
isScrollingDown = false;
}
lastVisibleItem = firstVisibleItem;
}
回答10:
Just set scroll listener to your listview.
If you have a header or footer you should check the visible count too. If it increases it means you are scrolling down. (Reverse it if there is a footer instead of header)
If you don't have any header or footer in your listview you can remove the lines which cheks the visible item count.
listView.setOnScrollListener(new AbsListView.OnScrollListener() {
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
if (mLastFirstVisibleItem > firstVisibleItem) {
Log.e(getClass().toString(), "scrolling up");
} else if (mLastFirstVisibleItem < firstVisibleItem) {
Log.e(getClass().toString(), "scrolling down");
} else if (mLastVisibleItemCount < visibleItemCount) {
Log.e(getClass().toString(), "scrolling down");
} else if (mLastVisibleItemCount > visibleItemCount) {
Log.e(getClass().toString(), "scrolling up");
}
mLastFirstVisibleItem = firstVisibleItem;
mLastVisibleItemCount = visibleItemCount;
}
public void onScrollStateChanged(AbsListView listView, int scrollState) {
}
});
and have this variables
int mLastFirstVisibleItem;
int mLastVisibleItemCount;
回答11:
For some reason the Android doc doesnt cover this, and the method used isnt even in the docs... took me a while to find it.
To detect if your scroll is at the top you would use this.
public boolean checkAtTop()
{
if(listView.getChildCount() == 0) return true;
return listView.getChildAt(0).getTop() == 0;
}
This will check if your scroller is at the top. Now, in order to do it for the bottom, you would have to pass it the number of children that you have, and check against that number. You might have to figure out how many are on the screen at one time, and subtract that from your number of children. I've never had to do that. Hope this helps
回答12:
Those methods cannot be used to detect scrolling directions directly. There are many ways of getting the direction. A simple code(untested) for one such method is explained below :
public class ScrollTrackingListView extends ListView {
private boolean readyForMeasurement = false;
private Boolean isScrollable = null;
private float prevDistanceToEnd = -1.0;
private ScrollDirectionListener listener = null;
public ScrollTrackingListView(Context context) {
super(context);
init();
}
public ScrollTrackingListView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public ScrollTrackingListView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
private void init() {
ViewTreeObserver observer = getViewTreeObserver();
observer.addOnGlobalLayoutListener(globalLayoutListener);
setOnScrollListener(scrollListener);
}
private ViewTreeObserver.OnGlobalLayoutListener globalLayoutListener
= new ViewTreeObserver.OnGlobalLayoutListener() {
@Override
public void onGlobalLayout() {
readyForMeasurement = true;
calculateDistanceToEnd();
}
};
public void registerScrollDirectionListener(ScrollDirectionListener listener) {
scrollDirectionListener = listener;
}
public void unregisterScrollDirectionListener() {
scrollDirectionListener = null;
}
private OnScrollListener scrollListener
= new OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView absListView, int i) {
calculateDistanceToEnd();
}
@Override
public void onScroll(AbsListView absListView, int i, int i1, int i2) {
// Do nothing
}
};
private void calculateDistanceToEnd() {
if (readyForMeasurement) {
// I'm using the height of the layout, horizontal scrollbar and
// content along with scroll down offset
// computeVerticalScrollExtent is used to compute the length of the thumb within the scrollbar's track.
// The length of the thumb is a function of the view height and the content length.
int verticalScrollExtent = computeVerticalScrollExtent();
int verticalScrollOffset = computeVerticalScrollOffset();
int verticalScrollRange = computeVerticalScrollRange();
int horizontalScrollBarHeight = getHorizontalScrollbarHeight();
/**
* 1. Let "R" represent the range of the vertical scrollbar. This corresponds to the length of the content
* in the view.
* 2. Let "E" represent the extent of the vertical scrollbar. The extent is a constant value and is
* (probably) equal to a value proportional to the height of the view.
* 3. Offset "o" represents the current position in the range that is visible to the user. It can take
* values from "0 to E".
*
* Now the DistanceToEnd is calculated using these three values as follows :
*
* DistanceToEnd = (R - o) / E
*
* DistanceToEnd will hold the value in NumberOfScreenToEnd units.
*
*/
float distanceToEnd =
((float)(verticalScrollRange - verticalScrollOffset))/((float)(verticalScrollExtent));
if(prevDistanceToEnd == -1) {
prevDistanceToEnd = distanceToEnd;
} else {
if(listener != null) {
if(distanceToEnd > prevDistanceToEnd) {
// User is scrolling up
listener.onScrollingUp();
} else {
// User is scrolling up
listener.onScrollingDown();
}
}
prevDistanceToEnd = distanceToEnd;
}
if(isScrollable == null) {
// Check if the view height is less than a screen (i.e., no scrolling is enabled)
if((horizontalScrollBarHeight + verticalScrollExtent) >= verticalScrollRange) {
isScrollable = Boolean.FALSE;
} else {
isScrollable = Boolean.TRUE;
}
}
}
}
public interface ScrollDirectionListener {
public void onScrollingUp();
public void onScrollingDown();
}
}
The idea is to calculate the distanceToEnd. If distanceToEnd increases, the user is scrolling up and if it decreases, the user is scrolling down. That will also give you the exact distance to the end of the list.
If you are just trying to know whether the user is scrolling up or down you can override the onInterceptTouchEvent to detect the scrolling direction like below :
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mInitialX = event.getX();
mInitialY = event.getY();
return true;
case MotionEvent.ACTION_MOVE:
final float x = event.getX();
final float y = event.getY();
final float yDiff = y - mInitialY; // yDiff less than 0.0 implies scrolling down while yDiff greater than 0.0 implies scrolling up. If I try to add the less than or greater than symbols, the preview refuses to display it.
if(yDiff less than 0.0) listener.onScrollingDown();
else if(yDiff greater than 0.0) listener.onScrollingUp();
break;
}
return super.onInterceptTouchEvent(event);
}
回答13:
Trick about detect scroll up or down in listview, you just call this function on onScroll function in OnScrollListener of ListView.
private int oldFirstVisibleItem = -1;
private protected int oldTop = -1;
// you can change this value (pixel)
private static final int MAX_SCROLL_DIFF = 5;
private void calculateListScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
if (firstVisibleItem == oldFirstVisibleItem) {
int top = view.getChildAt(0).getTop();
// range between new top and old top must greater than MAX_SCROLL_DIFF
if (top > oldTop && Math.abs(top - oldTop) > MAX_SCROLL_DIFF) {
// scroll up
} else if (top < oldTop && Math.abs(top - oldTop) > MAX_SCROLL_DIFF) {
// scroll down
}
oldTop = top;
} else {
View child = view.getChildAt(0);
if (child != null) {
oldFirstVisibleItem = firstVisibleItem;
oldTop = child.getTop();
}
}
}
回答14:
Simple way to detect scroll up/down on android listview
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount){
if(prevVisibleItem != firstVisibleItem){
if(prevVisibleItem < firstVisibleItem)
//ScrollDown
else
//ScrollUp
prevVisibleItem = firstVisibleItem;
}
dont forget
yourListView.setOnScrollListener(yourScrollListener);
回答15:
Here's what I would try first:
1) Create an interface (let's call it OnScrollTopOrBottomListener) with these methods:
void onScrollTop();
void onScrollBottom();
2) In your list's adapter, add a member instance, typed as the interface you created and supply a setter and getter.
3) In the getView() implementation of your adapter, check if the position parameter is either 0 or getCount() - 1. Also check that your OnScrollTopOrBottomListener instance is not null.
4) If the position is 0, call onScrollTopOrBottomListener.onScrollTop(). If position is getCount() - 1, call onScrollTopOrBottomListener.onScrollBottom().
5) In your OnScrollTopOrBottomListener implementation, call the appropriate methods to get the desired data.
Hope that helps in some way.
-Brandon
回答16:
I have encountered problems using some example where the cell size of ListView is great. So I have found a solution to my problem which detects the slightest movement of your finger . I've simplified to the minimum possible and is as follows:
private int oldScrolly;
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
View view = absListView.getChildAt(0);
int scrolly = (view == null) ? 0 : -view.getTop() + absListView.getFirstVisiblePosition() * view.getHeight();
int margin = 10;
Log.e(TAG, "Scroll y: " + scrolly + " - Item: " + firstVisibleItem);
if (scrolly > oldScrolly + margin) {
Log.d(TAG, "SCROLL_UP");
oldScrolly = scrolly;
} else if (scrolly < oldScrolly - margin) {
Log.d(TAG, "SCROLL_DOWN");
oldScrolly = scrolly;
}
}
});
PD: I use the MARGIN to not detect the scroll until you meet that margin . This avoids problems when I show or hide views and avoid blinking of them.
回答17:
Simple way to load more items on scroll up/down event in android GridView
grid.setOnScrollListener(new AbsListView.OnScrollListener() {
private int mLastFirstVisibleItem;
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// TODO Auto-generated method stub
Log.d("state",String.valueOf(scrollState));
if(scrollState == 0)
Log.i("a", "scrolling stopped...");
if (view.getId() == grid.getId()) {
final int currentFirstVisibleItem = grid.getLastVisiblePosition();
mLastFirstVisibleItem = grid.getFirstVisiblePosition();
if (currentFirstVisibleItem > mLastFirstVisibleItem) {
mIsScrollingUp = false;
if(!next.contains("null")){
//Call api to get products from server
}
Log.i("a", "scrolling down...");
} else if (currentFirstVisibleItem < mLastFirstVisibleItem) {
mIsScrollingUp = true;
Log.i("a", "scrolling up...");
}
mLastFirstVisibleItem = currentFirstVisibleItem;
}
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
Log.d("on scroll","");
}
});
来源：https://stackoverflow.com/questions/16791100/detect-scroll-up-scroll-down-in-listview