Develop Reference

Smooth Scroll Not Working on Initial Scroll for Android RecyclerView

I am working on an Android app that runs on only one devicerunning KitKat.
The smooth scrolling feature for a RecylerView I used that was working on other physical tablets and genymotion has unfortunately stopped working on the one device it needs to work on.
Instead of scrolling to a certain position it passes over the target position and scrolls all the way to the bottom and looks really bad.
I am able to track down the error to the abstract SmoothScroller in the RecyclerView class.
if (getChildPosition(mTargetView) == mTargetPosition) {
onTargetFound(mTargetView, recyclerView.mState, mRecyclingAction);
mRecyclingAction.runIfNecessary(recyclerView);
stop();
} else {
Log.e(TAG, "Passed over target position while smooth scrolling.");
mTargetView = null;
}
I was using a SnappingLinearLayoutManager that I found online, but swapped it out with the normal LinearLayoutManager from Android, and still am having the same problem.
The list is 7 items long (user can see 4 at a time) and I scroll to the 5th item (position 4) item.
When I scroll to the 3rd I don't receive this error.
Also after I scroll the list up and down once, the error stops happening.
EDIT:
I am able to use layoutManager.scrollToPositionWithOffset(); But I am trying to do this with the smooth scroll animation.
Here is some of my code and details:
private void setupMainRecyclerViewWithAdapter() {
mainLayoutManager = new SnappingLinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
mainListRecyclerView.setLayoutManager(mainLayoutManager);
settingsMainListAdapter = new SettingsListAdapter(SettingsActivity.this,
settingsPresenter.getSettingsItems(),
settingsPresenter);
mainListRecyclerView.setAdapter(settingsMainListAdapter);
mainListRecyclerView.addItemDecoration(new BottomOffsetDecoration(EXTRA_VERTICAL_SCROLLING_SPACE));
}
#Override
public void scrollMainList(boolean listAtTop) {
if(listAtTop) {
mainListRecyclerView.smoothScrollToPosition(4);
moveMainMoreButtonAboveList();
} else {
mainListRecyclerView.smoothScrollToPosition(0);
moveMainMoreButtonBelowList();
}
}

If you call recyclerView.smoothScrollToPosition(pos) will be called immediately on the UI thread and if recyclerView's Adapter is too much busy to generating view items then the calling of smoothScrollToPosition will be missed then because recyclerView has no data to smooth scroll. So it's better to do that in a background thread by recyclerView.post(). By calling this it goes into the Main thread queue and gets executed after the other pending tasks are finished.
Therefore you should do something like this which worked for my case:
recyclerView.post(new Runnable() {
#Override
public void run() {
recyclerView.smoothScrollToPosition(pos);
}
});

Well, I realize it's too late, however I tried some different solutions and found one...
in custom LinearSmoothScroller I override updateActionForInterimTarget
#Override
protected void updateActionForInterimTarget(Action action) {
action.jumpTo(position);
}
It's appears not very smooth, but not instant in contrast with scrollToPositionWithOffset.

Just add one line for smooth scroll
recyclerView.setNestedScrollingEnabled(false);
it will work fine

Take a look at hasPendingAdapterUpdates(). You can use this along with a delay() for coroutines or Thread.sleep() to enable the backing data to be available before doing the scroll.

floating View displaying on hover in android

I am trying to implement some hints when a user is hovering a button or another view, I see that android have support for onHoverListener but I don't understand how it really works. However I did try to find a solution how to make a floating editText on a button hover but I didn't find any ideas.
I am thinking that hover in android is the same think with long click because you can't hover with finger without clicking the view.

OnHoverListener is only implemented in 2 specific situations: a) when a Bluetooth or USB mouse is plugged into the device, or b) on Galaxy Note devices, when the S-Pen (stylus) is hovering over the object.
In specific setups/situations this can be a very neat feature, but unfortunately, most users will never even know it exists. For your situation, you may want to implement an OnLongClickListener for showing hints/tips as that is pretty standard in Android.
This example will show a TextView or ImageView hint for 5 seconds when a long-click is initiated:
btn.setOnLongClickListener(new View.OnLongClickListener() {
#Override
public boolean onLongClick(View view) {
findViewById(R.id.hint).setVisibility(View.VISIBLE);
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
public void run() {
findViewById(R.id.hint).setVisibility(View.GONE);
}
}, 5000);
return true;
}
});
Hope this helps,

I want to add up on Aaron's answer.
Some devices with sensitive screens - Samsung S5 comes to mind - don't even need an s-pen.
Just need to hold your finger 1/2 inch over the screen and it would trigger it.

Adjusting the scrollview at the bottom of the page

I have lots of contents on one page so i am using scrollview. I have one scan button at the bottom of the page, which i need to click many times to scan lots of barcodes. when i click on scan button, i am opening "BarcodeScanner" application that will sacn the barcode and returns the result to my application. so when i come back to my application, again i need to scroll the entire page to click the scan button which is at the bottom side. So is there any way to initialize the scroll at the bottom of the page? Please help
Thanks in advance

How do you think that you can initialise the scroll view.!! If you have lots of contents in a page you have to use scroll view for seeing all the contents. ! Try this, put your scroll view xml code in to botom of the xml code. and check.!!

Say your ScrollView id is scrollId, the code will lokk like this
scrollView = (ScrollView) findViewById (R.id.scrollId);
scrollView.post(new Runnable() {
#Override
public void run() {
scrollView.fullScroll(View.FOCUS_DOWN);
}
});

Try this
s.post(new Runnable() {
public void run() {
s.scrollTo(0, mScrollView.getBottom());
// or this
//s.fullScroll(s.FOCUS_DOWN);
}
});

How to simultaneously scroll two chart using AchartEngine?

I have an android application that uses AchartEngine to display two graphs. Everything is up and running and I can scroll each chart individually. However, I would like to be able to make the two charts scroll simultaneously, meaning that if scroll one chart, the other gets scrolled by the same amount. Does anyone have any pointers on how to proceed?
Thanks

You can add a listener on scrolling on each chart and change the other chart accordingly, something like this:
For the first chart mChartView_1
mChartView_1.addPanListener(new PanListener() {
public void panApplied() {
mRenderer_2.setRange(new double[] {
mRenderer_1.getXAxisMin(),
mRenderer_1.getXAxisMax(),
mRenderer_1.getYAxisMin(),
mRenderer_1.getYAxisMax()
});
}
});
and for the second chart mChartView_2
mChartView_2.addPanListener(new PanListener() {
public void panApplied() {
mRenderer_1.setRange(new double[] {
mRenderer_2.getXAxisMin(),
mRenderer_2.getXAxisMax(),
mRenderer_2.getYAxisMin(),
mRenderer_2.getYAxisMax()
});
}
});
Should work, but I didn't try it myself.

Add repaint() function to the above 2 code snippets. It will work only when we repaint.
mChartView_2.repaint(); // for mChartView_1 pan listener
mChartView_1.repaint(); // for mChartView_2 pan listener
Its late. But, hope it helps future readers.

Android Homescreen using a button to scroll to the next screen as well as the slide bit

I am making an app that has a scrolling screen like the homescreen style. I have implemented this solution:
Android Homescreen
It works great but I also want there to be buttons on each page that you can click to go to the next page but I just can't figure out how to do it! can someone help? I've been staring at this code for days now!
Thanks
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
UPDATE - HELP
I really don't understand how to get around the problem of calling the SetToScreen from the other activity, Can anyone help as if I try I do keep getting Static call errors.

Look at
public void setToScreen(int whichScreen) {}
Use this function to set to a screen on a click.
you should extend Draggablespace by adding a function to get the current space like:
public int getCurrentScreen() {
return this.mCurrentScreen;
}
then you can write your own functions in your activity like
public void nextScreen() {
draggableSpace.setToScreen(draggableSpace.getCurrentScreen() + 1));
}
The same for previous screen.
Now you only need to check if there is an additional screen waiting if you are going forward or backward.
(Of course draggableSpace is your object of the class draggablespace...not a static call!)