Develop Reference

AndroidStudio MotionEvent: detect only ACTION_UP on a second view, starting ACTION_DOWN on first view

Solved it by using emandt's suggestion. My personal Solution added below.
I'm using Android Studio for this.
I searched for solutions but couldn't find anything resembling this.
I want to know on which ImageView an UP action occurs while starting the DOWN action on a different ImageView (to eventually be able to drag one image over the other and make it snap to the same position by getting the position of the image I dragged over).
My example has two ImageViews with the id imageView (left) and imageView2(right).
In my example I'm not dragging anything yet, I just want to touch the left image, see "Action was down" in the log and lift the finger over the right image showing "Action was up2".
I don't know if this is easily possible.
As far as I can tell from testing, the MotionEvent.ACTION_UP only fires for an ImageView when you also pressed down on it beforehand. So when I release on top of imageView2 it only shows "Action was up" from the left image.
I wondered if it was possible by playing with return false, since the return value tells if an ActionEvent is consumed so I thought if the UP event of imageView returns false, maybe it does trigger the UP event of imageView2 but no. (Either complete misunderstanding on my part or it doesn't recognise UP on the second because it didn't start with a DOWN and MotionEvents probably always have to start with a DOWN).
public class MainActivity extends Activity {
ImageView imageView;
ImageView imageView2;
String DEBUG_TAG = "action";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
imageView = findViewById(R.id.imageView);
imageView2 = findViewById(R.id.imageView2);
imageView.setOnTouchListener(new View.OnTouchListener() {
public boolean onTouch(View v, MotionEvent event) {
//int action = MotionEventCompat.getActionMasked(event);
int action = event.getActionMasked();
switch(action) {
case (MotionEvent.ACTION_DOWN) :
Log.d(DEBUG_TAG,"Action was DOWN"+v.toString());
return true;
case (MotionEvent.ACTION_MOVE) :
//Log.d(DEBUG_TAG,"Action was MOVE");
return true;
case (MotionEvent.ACTION_UP) :
Log.d(DEBUG_TAG,"Action was UP"+v.toString());
return false;
default :
//return true;
}
return true;
}
});
imageView2.setOnTouchListener(new View.OnTouchListener() {
public boolean onTouch(View v, MotionEvent event) {
//int action = MotionEventCompat.getActionMasked(event);
int action = event.getActionMasked();
switch(action) {
case (MotionEvent.ACTION_DOWN) :
Log.d(DEBUG_TAG,"Action was DOWN2"+v.toString());
return true;
case (MotionEvent.ACTION_MOVE) :
//Log.d(DEBUG_TAG,"Action was MOVE");
return true;
case (MotionEvent.ACTION_UP) :
Log.d(DEBUG_TAG,"Action was UP2"+v.toString());
return true;
default :
//return true;
}
return true;
}
});
}
}
If there is no simple way to do this, I'm thinking about solving this mathematically, but maybe some of you can help.
So my question is, is there a way to recognise an UP action on a second ImageView while currently being in a MotionEvent of another ImageView?
SOLUTION (see emandt's answer)
I ditched the second OnClickListener because I realised that the 2nd image doesn't need any, I just need its position.
Added this method:
#Nullable
private View getDroppedView(View droppedView, int x, int y, List<View> arrayOfPossibilities) {
Rect cVisibleBoundsRect = new Rect();
for (View cView : arrayOfPossibilities) {
//if currently iterated view doesn't have values for getGlobalVisibleRect, skip the .contains part
//ignore the item which is your current active item (which would potentially be dropped)
//getGlobalVisibleRect sets cVisibleBoundsRect immediately to the Rect given as parameter
if (!cView.getGlobalVisibleRect(cVisibleBoundsRect)||(cView.equals(droppedView))) continue;
if (cVisibleBoundsRect.contains(x, y)) {
Log.d(DEBUG_TAG,"Found something");
//THIS "cView" IS THE VIEW WHERE YOU RELEASED THE FINGER
return cView;
}
}
Log.d(DEBUG_TAG,"Found nothing");
return null;
}
And added this in onUP:
case (MotionEvent.ACTION_UP) :
View dropTarget;
Log.d(DEBUG_TAG,"Action was UP"+v.toString());
dropTarget = getDroppedView(v, (int)event.getRawX(), (int)event.getRawY(), listOfViews);
if (dropTarget != null){
v.setX(dropTarget.getX());
v.setY(dropTarget.getY());
}

I think you want to know which is the View where you release the finger from the screen, am I right?
To do this you can use the same "View.OnTouchListener()" for all of your Views and in the ACTION_UP you have to call a new method similar to this (pseudo-code):
....
case (MotionEvent.ACTION_UP) :
View[] cArrayOfPossibileViews = new View[]{ findViewById(IMAGE_1), findViewById(IMAGE2) }
getDroppedView(v, event.getRawX(), event.getRawY(), cArrayOfPossibileViews);
break;
}
....
#Nullable
private View getDroppedView(View view, int x, int y, View[] arrayOfPossibilities) {
Rect cVisibleBoundsRect = new Rect();
for (View cView : arrayOfPossibilities) {
if (!cView.getGlobalVisibleRect(cVisibleBoundsRect)) continue;
if (cVisibleBoundsRect.contains(x, y)) {
//THIS "cView" IS THE VIEW WHERE YOU RELEASED THE FINGER
return cView;
}
}
return null;
}
This method get View bounds and compare them avains X and Y of your Touch Event. If X and Y are contained inside a View bounds it means that View is the one you need.

How to distinct between a tap on the right/ left side of the display?

I thought this is a pretty relevant and common question, but I couldnt find an answer.
At the moment I have this method:
public boolean onTouchEvent (MotionEvent evt){
if (evt.getAction() == MotionEvent.ACTION_DOWN) {
do stuff ...
}
}
So if the user taps on the screen (wherever) the code is executed. Now I want the distinction between the right side of the display and the left side (left side means --> go back).

You can do this many ways. Here is one of them:
Attach onTouch listener to the view, which stretches to its edges. (For example your RelativeLayout which holds rest of views)
private View.OnTouchListener onTouchListener = new View.OnTouchListener() {
#Override
public boolean onTouch(View v, MotionEvent event) {
float halfOfAScreen = mainLayout.getMaxWidth() / 2;
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
float fingerPosition = event.getX();
if(fingerPosition < halfOfAScreen) {
onBackPressed();
}
return true;
default:
return false;
}
}
};

Refer to this post on how to get touch position.
It seems in your case you will use
int x = (int)event.getX();
int y = (int)event.getY();
and work within the bounds of your layout that you want the app to react to.

Swipable Linear/Relative Layout (part 2)

I posted a question yesterday [ Swipable Linear/Relative Layout ]. The question did not get any answers. Meanwhile, I tried to solve my own problem. What I did is that I used the OnTouchListener to detect swipe and thus toggle the scientific part of the calculator (Read the question I posted earlier to get a clear idea) I used the following code :-
RelativeLayout layout = (RelativeLayout)findViewById(R.id.advanced);
layout.setOnTouchListener(new View.OnTouchListener() {
#Override
public boolean onTouch(View v, MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
downX = event.getX();
return true;
}
case MotionEvent.ACTION_MOVE: {
upX = event.getX();
float deltaX = downX - upX;
swipe((int) deltaX);
return true;
}
case MotionEvent.ACTION_UP: {
downX = 0;
}
}
return true;
}
and the swipe method is :-
private void swipe(int distance) {
RelativeLayout layout = (RelativeLayout)findViewById(R.id.advanced);
LinearLayout.LayoutParams head_params = (LinearLayout.LayoutParams)layout.getLayoutParams();
head_params.setMargins(-distance, 0, 0, 0); //substitute parameters for left, top, right, bottom
layout.setLayoutParams(head_params);
}
The code works fine and achieves what it was meant to be till a certain extent. The problem is that, the swipe is buggy,i.e., it kind of flashes when I swipe it and also, it is very slow. Please tell me how to implement this correctly. Shall I use ViewPager or something else. Please enlighten me. Thanks

The reason this is buggy is because you've registered a touch listener on the view you're moving as well. This causes the touch listener to return 'twitchy' values. One approach you could take is putting the listener on a parent view that is stationary, and using that to update the child view. I would also recommend looking into using a GestureDetector instead, it does most of the touch logic for you and provides some very useful methods through a listener.

How to have a touch listener and still be able to scroll

I have a listview and I set an onClickListener and an onTouchListener. The click listener for when they click on an item, I had just this and everything thing worked fine. But, when I added the touch listener to watch for left and right swipes, it won't let me scroll anymore.
listview.setOnTouchListener(new OnTouchListener(){
public boolean onTouch(View v, MotionEvent event){
switch (event.getAction()){
case MotionEvent.ACTION_DOWN:
historicX = event.getX();
historicY = event.getY();
break;
case MotionEvent.ACTION_UP:
if(event.getX() - historicX < -DELTA){
slidingLeft(event.getX(),event.getY());
return true;
}
else if(event.getX() - historicX > DELTA){
slidingRight(event.getX(), event.getY());
return true;
}
break;
default: return true;
}
return false;
}
});
How can I have to able to scroll through the listview again. Is there another listener I could add to do this, or could I modify the onTouchListener to watch for scrolls too?

You should use GestureDetector .
You can use example from here, it is very clear.
https://stackoverflow.com/a/12938787/1374065

Override single tap of Photoview

I have an ImageView inside of a view pager with an ActionBar at the top. I would like to be able to single tap to hide the action bar, and I would also like to be able to pinch zoom and pan on each ImageView.
To implement the single tap to hide the action bar I have a simple OnClickListener that hides it.
To implement the pinch zoom and pan on each ImageView I am using the PhotoView Library Project.
I am having issues because only one touch event listener can be associated with an ImageView, and the implementing the PhotoView Library project overwrites my OnClickListener to hide the ActionBar with,
parent.requestDisallowInterceptTouchEvent(true);
I am not sure how to go about getting both implemented at the same time. It seems like the only solution is to create my own Pinch Zoom ImageView in order to control touch events myself.

Found out that the PhotoView library actually allows me to set onViewTap for the PhotoViewAttacher object which is exactly what I wanted.
To create the PhotoViewAttacher in the current Fragment/Activity have it implement PhotoViewAttacher.OnViewTapListener, create the attacher,
PhotoViewAttacher mAttacher = new PhotoViewAttacher(imageView);
mAttacher.setOnViewTapListener(this);
and add the following function,
public void onViewTap(View view, float x, float y) {
// your code here
}
Source

You'll have to override the PhotoView library itself. If you look at the source code, the PhotoViewAttacher class is the one that handles the onTouch events.
You'll have to add the special funcionality you're looking for at this part of the code (specially, the ACTION_DOWN) event:
#Override
public final boolean onTouch(View v, MotionEvent ev) {
boolean handled = false;
if (mZoomEnabled && hasDrawable((ImageView) v)) {
ViewParent parent = v.getParent();
switch (ev.getAction()) {
case ACTION_DOWN:
// First, disable the Parent from intercepting the touch
// event
if (null != parent)
parent.requestDisallowInterceptTouchEvent(true);
else
Log.i(LOG_TAG, "onTouch getParent() returned null");
// If we're flinging, and the user presses down, cancel
// fling
cancelFling();
break;
case ACTION_CANCEL:
case ACTION_UP:
// If the user has zoomed less than min scale, zoom back
// to min scale
if (getScale() < mMinScale) {
RectF rect = getDisplayRect();
if (null != rect) {
v.post(new AnimatedZoomRunnable(getScale(), mMinScale,
rect.centerX(), rect.centerY()));
handled = true;
}
}
break;
}
// Check to see if the user double tapped
if (null != mGestureDetector && mGestureDetector.onTouchEvent(ev)) {
handled = true;
}
if (!handled && null != parent) {
parent.requestDisallowInterceptTouchEvent(false);
}
// Finally, try the Scale/Drag detector
if (null != mScaleDragDetector
&& mScaleDragDetector.onTouchEvent(ev)) {
handled = true;
}
}
return handled;
}