Android scrollview onScrollChanged
I have a fixed content in my text view inside a scroll view. When the user scrolls to a certain position, I would like to start an activity or trigger a Toast
.
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent" android:layout_height="fill_parent"
android:id="@+id/scroller">
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="开发者_开发知识库fill_parent">
<TextView android:layout_width="fill_parent" android:id="@+id/story"
android:layout_height="wrap_content" android:text="@string/lorem"
android:gravity="fill" />
</LinearLayout>
</ScrollView>
My problem is in implementing the protected method onScrollChanged
to find out the position of the scroll view.
I have found this answer, is there an easier solution to this rather than declaring an interface, over ride the scrollview etc as seen on the link I posted?
There is a much easier way than subclassing the ScrollView
. The ViewTreeObserver
object of the ScrollView
can be used to listen for scrolls.
Since the ViewTreeObserver
object might change during the lifetime of the ScrollView
, we need to register an OnTouchListener
on the ScrollView
to get it's ViewTreeObserver
at the time of scroll.
final ViewTreeObserver.OnScrollChangedListener onScrollChangedListener = new
ViewTreeObserver.OnScrollChangedListener() {
@Override
public void onScrollChanged() {
//do stuff here
}
};
final ScrollView scrollView = (ScrollView) findViewById(R.id.scroller);
scrollView.setOnTouchListener(new View.OnTouchListener() {
private ViewTreeObserver observer;
@Override
public boolean onTouch(View v, MotionEvent event) {
if (observer == null) {
observer = scrollView.getViewTreeObserver();
observer.addOnScrollChangedListener(onScrollChangedListener);
}
else if (!observer.isAlive()) {
observer.removeOnScrollChangedListener(onScrollChangedListener);
observer = scrollView.getViewTreeObserver();
observer.addOnScrollChangedListener(onScrollChangedListener);
}
return false;
}
});
No.
ScrollView doesn't provide a listener for scroll events or even a way to check how far down the user has scrolled, so you have to do what is suggested by the link.
This question is fairly old, but in case somebody drops by (like me):
Starting with API 23, Android's View
has a OnScrollChangeListener
and the matching setter.
The NestedScrollView from the Support library also supports setting a scroll listener even before that API level. As far as I know, NestedScrollView
can be used as a replacement for the normal ScrollView
without any problems.
Actually there is a way to know how far the user has scrolled. The method getScrollY() from ScrollView tells you that.
I extended my scrollView. This link may help.
class MyScroll extends ScrollView {
boolean onTop=true;
@Override
protected void onScrollChanged(int l, int t, int oldl, int oldt) {
//Log.d(TAG, "scroll changed: " + this.getTop() + " "+t);
if(t <= 0){
onTop = true;
//Log.d(TAG, "scroll top: " + t);
super.onScrollChanged(l, t, oldl, oldt);
return;
// reaches the top end
}
onTop = false;
View view = (View) getChildAt(getChildCount()-1);
int diff = (view.getBottom()-(getHeight()+getScrollY()+view.getTop()));// Calculate the scrolldiff
if( diff <= 0 ){
// if diff is zero, then the bottom has been reached
}
super.onScrollChanged(l, t, oldl, oldt);
}
}
you can use this trigger to show Toast or Start Activity
scrollView.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
@Override
public void onScrollChanged() {
// do something when Scroll
}
});
you can use this code to detect is up or down scroll
scrollView.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
int lastScroll=0;
@Override
public void onScrollChanged() {
int scrollY = scrollView.getScrollY(); // For ScrollView herzontial use getScrollX()
if (scrollY > lastScroll ) {
Log.e("scroll","down scroll"+scrollY);
} else if (scrollY < lastScroll ) {
Log.e("scroll","up scroll"+scrollY);
}
lastScroll=scrollY;
}
});
NestedScrollView is just like android.widget.ScrollView, but it supports acting as both a nested scrolling parent and child on both new and old versions of Android.
1st - Use NestedScrollView binding instead ScrollView
2nd - Set Scroll listener, like this, to detect axis Y moving for a headerView by example
nestedScrollView.setOnScrollChangeListener(new NestedScrollView.OnScrollChangeListener() {
@Override
public void onScrollChange(NestedScrollView v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {
Log.d(TAG, "onScrollChangeForY - scrollY: " + scrollY + " oldScrollY: " + oldScrollY);
int MOVE = -1, SCROLL_UP = 0, SCROLL_DOWN = 1;
float initialPositionY = headerView.getY();
MOVE = scrollY > oldScrollY ? SCROLL_UP : SCROLL_DOWN;
if (MOVE == SCROLL_UP) {
int incrementY = scrollY - oldScrollY;
headerView.setY(initialPositionY - incrementY);
} else {
int incrementY = oldScrollY - scrollY;
headerView.setY(initialPositionY + incrementY);
}
}
});
There is ready for use component, which helps to listen to scroll events of arbitrary views in Android. Internally this component adds ViewTreeObserver scroll events listener on devices with old Android API (similar as proposed in Shubhadeep Chaudhuri's answer) and View scroll events listener on devices with new Android API (API level 23+).
Just use NestedScroll
and NestedScroll.setOnScrollChangeListener()
.
Starting from API 23 Android M, you can use OnScrollChangeListener.
scrollView.setOnScrollChangeListener(new View.OnScrollChangeListener() {
@Override
public void onScrollChange(View v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {
//work with parameters
}
});
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