I've seen many questions (and answers) regarding ViewTreeObserver but none have completely answer the question/problem i'm facing. So here's what i have:
I have some views being added programmatically inside a scrollview. After all the layout has been set I want to scroll to a specific view that is inside the scrollview. For this I'm using View Tree Observer and the code is as follows (Some pseudo of what I'm doing)
viewInsideScrollView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
#Override
public synchronized void onGlobalLayout() {
firstTime++; // Counts how many times I enter the listener
if (firstTime == 1) {
// Here the fully measure of the scroll view has not happened
} else if (firstTime == 2) {
// I still don't have the full measure of the scroll view (Let's say that, for example, paddings are missing/weren't calculated)
} else if (firstTime == 3) {
// Here is when I can safely get the locationOfTheView variable and the scroll down will happen perfectly!
viewInsideScrollView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
scrollView.scrollTo(0, locationOfTheView);
}
}
});
Note: The reason I add firstTime == 3 is because, in this specific case, I noticed that it only calls the global layout 3 times.
So my question is as follows: How can I detect, cleanly, when the Global Layout has finished all the necessary measurements?
Yes I have some work arounds that works like adding a small delay which will give time for the Global Layout to have it's measures done but I was looking for another (cleaner) way to do that.
Any ideas?
Thanks!
I have a fragment and I need to measure location/width/height of its views on screen and pass to some other class.
So what I have is a function which does it, something like this :
private void measureTest(){
v = ourView.findViewById(R.id.someTextField);
v.getLocationOnScreen(loc);
int w = v.getWidth();
...
SomeClass.passLocation(loc,w);
...
The problem is that the location/width/height of views is not ready within fragment lifecycle.
So if I run that function within these lifecycle methods :
onCreateView
onViewCreated
onStart
onResume
I either get wrong location and width/height measurments or 0 values.
The only solution I found is to add a GlobalLayoutListener like this to mainView
mainView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
public void onGlobalLayout() {
if(alreadyMeasured)
mainView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
else
measureTest();
}
});
this gets the job done.. but its just Yack! IMO.
Is there a better way of doing this? seems like such a basic thing to do
inside onActivityCreated of your fragment retrieve the currentView (with getView()) and post a runnable to its queue. Inside the runnable invoke measureTest()
There is no better way. That code isn't that bad! It's fired as soon as the view is layed out (my terminology might be a bit weird there) which happens right after measuring. That is how it is done in the BitmapFun sample (see ImageGridFragment, line 120) in Google's Android docs. There is a comment on that particular piece of code stating:
// This listener is used to get the final width of the GridView and then calculate the
// number of columns and the width of each column. The width of each column is variable
// as the GridView has stretchMode=columnWidth. The column width is used to set the height
// of each view so we get nice square thumbnails.
In my app I have a header with icon hidden, I have a adapter with a listview when I click the listview I go to a login screen using listener, when the login is successful is should come back to listview(adapter) and icon should get visible on header.
In the login activity I have the following code:
public void onClick(View v) {
String password = etPassword.getText().toString();
if(password.equals("guest")){
SearchAdapter.setImgVisibility();
} else {
//-----
}
finish();
}
In my adapter I am calling the setImgVisibility() as follows, but it is not working
public static void setImgVisibility() {
img.setVisibility(View.VISIBLE);
}
I am getting a Nullpointerexception near the line img.setVisibility(View.VISIBLE);
I am stuck here and don't know what I am doing wrong. Any suggestions or help is appreciated
I would imagine that img is null. You need to look at where this value is set and make sure happens before you call the method setImgVisibility.
Show more of your complete code for people to help further.
Additionally, i've just noticed you've used a static reference to your search adapter, you should be really careful using statics, especially where any referencing of images is concerned as images can be bound to the context, as such unless you nullify the static you will end up with a memory leak. (this used to be an old problem, not sure its still valid, but i would still avoid using a static reference).
Without more code we're not likely to be able to properly help you. For example are you switching activities when logging in? If you are, this won't work at all.
[given the comment below] If you switch activities then your activity containing the list view is going to be destroyed and then rebuilt then you navigate back to it. or it will at least go through the activity lifecycle. This means you can set the icon during the instantiation of the header img.
You could store your logged in state as a property of the Application or a preference. Grab this value when you set the header image and set the image accordingly.
your img object is null. Is your img object is same as View v then you can pass v in setImgVisibility() and then set v.setVisibility(View.VISIBLE)
I am trying to add some visual indication, that there are no more pages in the desired fling direction in the ViewPager. However I am struggling to find a place, where to put relevant code.
I have tried extending ViewPager class with following code, but the Toast is not displaying (ev.getOrientation() returns always 0). I have also tried the same with history points, but ev.getHistorySize() returns also 0.
What am I missing?
Class example:
public class CustomViewPager extends ViewPager {
public CustomViewPager(Context context) {
super(context);
}
public CustomViewPager(Context context, AttributeSet attrs) {
super(context, attrs);
}
/**
* #see android.support.v4.view.ViewPager#onTouchEvent(android.view.MotionEvent)
*/
#Override
public boolean onTouchEvent(MotionEvent ev) {
boolean result = super.onTouchEvent(ev);
switch (ev.getAction() & MotionEventCompat.ACTION_MASK) {
case MotionEvent.ACTION_MOVE:
if (ev.getOrientation() > 0) {
Toast.makeText(getContext(), "left", 0).show();
}
}
return result;
}
}
If you look at the v4 support library you will see there's a class used by ViewPager called EdgeEffectCompat (this provides the glow effect when you reach the beginning or end of a view pager in ICS+) If you look at the implementation in the compat library you will see that it has an if-statement to see if the build version is 14+ (ICS) or not. If it is, then it ends up eventually (if you trace long enough) using the normal EdgeEffect class that was inroduced in ICS. Otherwise it uses BaseEdgeEffectImpl which basically has nothing in it.
If you want, you can make your own custom ViewPager that uses EdgeEffect of your own. You can look at the android source code to see how they implemented EdgeEffect here which you can pretty much copy (just make sure to copy the overscroll_edge and overscroll_glow drawables in the AOSP /res/drawable directories to your own project since they are internal to android) or go ahead and create your own version.
Good luck.
(By the way, that's how they create the cool looking edge tilt effect in the launcher menu on ICS... so you can pretty much be as creative as you want with this ;)
I was trying to get the exact same effect that was asked in this question. I struggle with it and then I read #wnafee answer (I couldn't do it with out it).
But then I struggle to implement what was sound pretty simple from the answer.
I had so much trouble with implementing it, that I might didn't understand the answer correctly, but there were too many issues of inaccessible APIs since I wasn't working in the same package of the Compatibility library.
After I tried some approaches (none of them succeeded, and they were pretty complicated) I went to a slightly different direction, and now it works like a charm. I used some reflection, for the ones who never used it, don't worry it is really the basic of reflection.
I'm not sure if it's the best solution out there, but it worked for me, so if you would like to use it you are welcome. Please read Wnafee example since it explains some of the stuff that I did.
In order to accomplish this task you should just follow my three parts solution. (Will take you between 3-10 minutes)
Part I:
As Wnafee said I just made my own EdgeEffect class by copy paste the source code from here,
(just make sure to copy the overscroll_edge and overscroll_glow
drawables in the AOSP /res/drawable directories to your own project
since they are internal to android)
I only did 2 really small changes:
I declare that the class extends EdgeEffectCompat (I called my class EdgeEffectForEarlyVersions). public class EdgeEffectForEarlyVersions extends EdgeEffectCompat. The reason for doing this change is that the mLeftEdge and mRightEdge are of the type EdgeEffectCompat.
At the first line of the constructor of "my" new class I added a call to the parent constructor super(context);. Since there is no default constructor to EdgeEffectCompat you have to Explicitly call the constructor.
Part II
Besides that I wrote the another function. The purpose of the function is that in case of an early version (before ICS) we would like to use the EdgeEffectForEarlyVersions that we just copied. In order to get that purpose I used reflection.
This is the function:
private static void changeEdgeEffectCompactOnEarlyVersions(ViewPager viewPager, Context context)
{
/* In case that the version is earlier than 14 there is only empty implementation for the edge effect, therefore we change it.
* for more information look on the following links:
* 1. http://stackoverflow.com/questions/10773565/visual-indication-of-over-scroll-in-android
* 2. http://grepcode.com/file/repo1.maven.org/maven2/com.google.android/support-v4/r7/android/support/v4/view/ViewPager.java#ViewPager.0mLeftEdge
* 3. http://grepcode.com/file/repo1.maven.org/maven2/com.google.android/support-v4/r7/android/support/v4/widget/EdgeEffectCompat.java#EdgeEffectCompat
*/
if (Build.VERSION.SDK_INT < 14)
{
try
{
Class<ViewPager> viewPagerClass = ViewPager.class;
//Get the left edge field, since it is private we used getDeclaredField and not getDeclared
Field leftEdge = viewPagerClass.getDeclaredField("mLeftEdge");
leftEdge.setAccessible(true);
//Get the right edge field, since it is private we used getDeclaredField and not getDeclared
Field rightEdge = viewPagerClass.getDeclaredField("mRightEdge");
rightEdge.setAccessible(true);
EdgeEffectForEarlyVersions leftEdgeEffect = new EdgeEffectForEarlyVersions(context);
EdgeEffectForEarlyVersions rightEdgeEffect = new EdgeEffectForEarlyVersions(context);
//Set the mLeftEdge memeber of viewPager not to be the default one, but to be "our" edgeEffect
leftEdge.set(viewPager, leftEdgeEffect);
//Set the mRightEdge memeber of viewPager not to be the default one, but to be "our" edgeEffect
rightEdge.set(viewPager, rightEdgeEffect);
}
catch (Exception ex)
{
Log.e("refelection", ex.getMessage());
}
}
}
Part III
Now all there is left to do, is to call that function after you have the ViewPager Instance and nothing more.
I Hope it will help someone.
wnafee explained the solution well but for the lazy among us, i made an actual working implementation quite some time ago.
https://github.com/inovex/ViewPager3D
And if you just want overscroll take a look here:
https://github.com/inovex/ViewPager3D/issues/1
You have a lot of options, you can show a Toast, display a Dialog, make a TextView or image to appear over your UI, etc. Or because you know the amount of View items in the ViewPager, you could add different View at positions 0 and/or n + 1 with the message and make it bounce to the last View that actually contains your data.
You could implement:
viewPager.setOnPageChangeListener(new OnPageChangeListener() {
public void onPageSelected(int position) {
//TODO If position is the 0 or n item, add a view at 0 or at n+1 to indicate there is no more pages with data.
}
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
// TODO Show a Toast, View or do anything you want when position = your first/last item;
}
public void onPageScrollStateChanged(int state) {
}
});
just to complement #goBeepit dev answer when you create your own edgeffect class and you extend from EdgeEffectCompat some methods requires to be boolean. you can change those methods to boolean type and make then return true in any case, this way everything works fine
You can overload the setUserVisibleHint(boolean) function in your fragments. Pseudo code:
void setUserVisibleHint(boolean isVisibleToUser) {
// If this fragment is becoming visible
if (isVisibleToUser == true) {
// Check if it is the last fragment in the viewpager
if (indexOfThis == getActivity().indexOfLast) {
// Display right limit reached
Toast(..., "No more Frags to right",...)
}
// Check if it is the first fragment in the viewpager
else if (indexOfThis == getActivity().indexOfFirst) {
// Display Left Limit reached
Toast(..., "No more Frags to left",...)
}
}
}
I have not used this function for this purpose, but have used it for other reasons and it does fire appropriately. Hope this helps...
I've implemented a bounce back effect based on Renard's ViewPager3D: https://stackoverflow.com/a/17425468/973379
Usually with ViewPager, one uses a PagerAdapter such as FragmentPagerAdapter or FragmentStatePagerAdapter to flood the ViewPager with contents(your content are going to be views).
Now, when you use a PagerAdapter, you have one method called getCount(), http://developer.android.com/reference/android/support/v4/view/PagerAdapter.html#getCount%28%29 ,which will give you the size of the content.
Since you now, know the size you can easily display a message with an if control statement.
Try this code : http://developer.android.com/reference/android/support/v4/view/ViewPager.html
Note: I dont think you need a custom ViewPager. You will also need to understand Fragments for ViewPager. Look at samples in ApiDemos. Its a great source.
I have a view (custom drawn) added with getWindowManager().addView() and later I'm modifiying the LayoutParameters of it (changing x & width) and call getWindowManager().updateViewLayout(). This works but I am getting two screen refreshes, first one only moves the whole thing according to the new x and later one scales it according to the new width. Any ideas about why is this happening even though I only call updateViewLayout just one time with the new layout parameters?
FYI: onDraw method of the custom drawn view mentioned here is also called only one time by the system during this process.
Try:
runOnUiThread(new Runnable() {
public void run() {
view.updateViewLayout();
}
});
http://developer.android.com/reference/android/app/Activity.html#runOnUiThread(java.lang.Runnable)
If it doesn't work, check this:
How to move a view in Android?
Are you doing this?
try to do :
view.post(new Runnable() {
public void run() {
view.updateViewLayout();
}
});
updateViewLayout is an a method that can be overriden by your custom ViewGroup and in this overrided method you can implement all what your want to change.
Maybe you do something wrong in it?
Or also maybe you have to implement this code in UiThread like in other questions. - In this case when you change your parameters asynchronously with first call of drawing function by system you method maybe can change only one parameter and on second call the second parameter will be also changed.