Android Multi-Touch pointerIndex out of range - android

Code from this book: Programming Android, 2nd Edition.
At first I touch the screen with two fingers - everything OK.
Then touch the screen with one finger - java.lang.IllegalArgumentException: pointerIndex out of range
public boolean onTouch(View v, MotionEvent event) {
int action = event.getActionMasked();
int idx;
int n;
switch (action) {
case MotionEvent.ACTION_DOWN:
case MotionEvent.ACTION_POINTER_DOWN:
idx = MotionEventCompat.getActionIndex(event);
tracks.add(event.getPointerId(idx));
break;
case MotionEvent.ACTION_POINTER_UP:
idx = MotionEventCompat.getActionIndex(event);
tracks.remove(event.getPointerId(idx));
break;
case MotionEvent.ACTION_MOVE:
n = event.getHistorySize();
for (Integer i : tracks) {
idx = event.findPointerIndex(i.intValue());
for (int j = 0; j < n; j++) {
addDot(
dots,
event.getHistoricalX(idx, j),
event.getHistoricalY(idx, j),
event.getHistoricalPressure(idx, j),
event.getHistoricalSize(idx, j)
);
}
}
break;
default:
return false;
}
for (Integer i: tracks){
idx = event.findPointerIndex(i.intValue());
addDot(
dots,
event.getX(idx),
event.getY(idx),
event.getPressure(idx),
event.getSize(idx)
);
}
return true;
}

The method findPointerIndex() may return -1. From what I have experienced this will happen when you touch with 2 fingers (or more) and let go of the first pressed finger.
I think this is the cause of 'pointerIndex out of range' error - since -1 is not a valid index :-)
For ACTION_MOVE I would recommend using a loop with getPointerCount(), ie looping from 0 to getPointerCount() - 1.
Using this method you can get touch position with getX(finger) and getY(finger).
Where 'finger' is your loop count.
Using this method will not keep track of what ID your finger has, ie if you press with two fingers and let go the first finger (ID=0) then the second finger will continue to count as the first finger (which is now not pressed)
Hope this helps!
/Richard

Related

Android Multitouch Strange Behavior

After a lot of tinkering, I think I've finally come up with a good multitouch handling system for my android game. It makes use of Robert Greene's Input Pipeline, modified for use with multitouch. Right now, the code has a simple system that records which pointer ID is currently doing which action (right now just shooting and moving). Each pointer's state is kept in a Pointer class, which is just a simple encapsulation of whether it is down, and it's coordinates. The ID acts as the pointer array index.
This seems like it should work well in practice, but in game it behaves very erratic. When recording the pointer actions in LogCat, oftentimes Android will send an "UP" action when the pointer remains down, or just before a number of "MOVE" actions by the pointer. Because my code believes the pointer is up, the game doesn't respond to it.
This also happens with button presses like the shooting button. When the pointer comes down on the area (which right now is just simply the lower left region), Android will send multiple "UP" and "DOWN" actions even though the pointer remains down the whole time. I had a single touch movement system before and none of these problems happened.
Is this just an issue with how I am reacting to the events? Should I handle POINTER_DOWN and DOWN separately? Or should I detect which pointers are moving after the "UP" action to see which ones really are down despite what Android says?
Here's my current code in my thread which receives the input events from Android. Because it is a pipeline system, I have the events encapsulated in the InputObject which is somewhat similar to Robert Greene's. Maybe a new set of eyes can help me tell what's wrong? Thanks for any help!
private int inx, iny;
private int shootID;
public boolean shooting = false;
private int moveID;
public boolean moveDown = false;
private static final int MAX_POINTERS = 10;
private Pointer[] pointers = new Pointer[MAX_POINTERS];
public void inputTouch(InputObject in) {
switch(in.action) {
case MotionEvent.ACTION_DOWN:
case MotionEvent.ACTION_POINTER_DOWN:
pointers[in.pID].press(in.pX[in.actionIndex], in.pY[in.actionIndex]);
//Log.i("D", "DOWN");
break;
case MotionEvent.ACTION_MOVE:
for(int p = 0; p < in.pointCount; p++) {
int id = in.pointerIDs[p];
pointers[id].setCoord(in.pX[id], in.pY[id]);
}
//Log.i("D", "MOVE");
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_POINTER_UP:
pointers[in.pID].release();
if(shootID == in.pID) {
shooting = false;
}
if(moveID == in.pID) {
moveDown = false;
}
//Log.i("D", "UP");
break;
case MotionEvent.ACTION_CANCEL:
default:
break;
}
for(int ap = 0; ap < MAX_POINTERS; ap++) {
if(pointers[ap].down) {
if(pointers[ap].x < world.cam.pixelWidth / 4 &&
pointers[ap].y > world.cam.pixelHeight - (world.cam.pixelHeight / 4)) {
shootID = ap;
shooting = true;
} else {
inx = pointers[ap].x;
iny = pointers[ap].y;
moveID = ap;
moveDown = true;
}
}
}
StringBuilder sb = new StringBuilder();
for(int j = 0; j < 3; j++) {
sb.append("ID " + (j+1) + ": " + pointers[j].down + "[" + pointers[j].x + ", " + pointers[j].y + "]" + " | ");
}
//Log.i("D", sb.toString());
}
Hope you got the answer by now, but here''s my solution:
First of all, there's a couple of things to add in the InputHolder class:
-internal public fields for mPointerIndex = event.getPointerIndex and mPointerID = event.getPointerID(mPointerIndex) (these get assigned in the useEvent/useHistory)
-if you only need to track 2 touchpoints, you need to add mPointerIndex2, x2 and y2 aswell. Add more as you need to track more points.
-add definitions for the case where MotionEvent.ACTION_POINTER_2_UP/DOWN gets passed. Turns out, POINTER_1 is the same as POINTER_UP/DOWN! This really tripped me up because I was falling through the switch case to the default. I only caught this because I changed my default to -1 and saw it logged.
Depending on how you process the actions in your processInput(obj), you map these to different ints. In my case I used the obj.y to see if they where left/right touches and I only needed two points, so I mapped these to ACTION_TOUCH_POINTER_UP/DOWN instead of giving each touch it's own action int identifier.
-now, if you want to track multiple touch points, you would have to do the above and the below in a for loop over all entries in event.getPointerCount(). In my case I was only interested in the x/y of one other touchpoint, so I could get away with only doing a check after I had filled the first point and the other pointerindex was easy to deduce:
public void useEvent(MotionEvent event) {
eventType = EVENT_TYPE_TOUCH;
int a = event.getAction();
switch (a) {
case MotionEvent.ACTION_DOWN:
action = ACTION_TOUCH_DOWN;
break;
case MotionEvent.ACTION_POINTER_DOWN:
action = ACTION_TOUCH_POINTER_DOWN;
break;
case MotionEvent.ACTION_POINTER_2_DOWN:
action = ACTION_TOUCH_POINTER_DOWN;
break;
case MotionEvent.ACTION_MOVE:
action = ACTION_TOUCH_MOVE;
break;
case MotionEvent.ACTION_UP:
action = ACTION_TOUCH_UP;
break;
case MotionEvent.ACTION_POINTER_UP:
action = ACTION_TOUCH_POINTER_UP;
break;
case MotionEvent.ACTION_POINTER_2_UP:
action = ACTION_TOUCH_POINTER_UP;
break;
default:
action = -1;
}
time = event.getEventTime();
pointerIndex = (event.getAction() & MotionEvent.ACTION_POINTER_ID_MASK) >> MotionEvent.ACTION_POINTER_ID_SHIFT;
pointerID = event.getPointerId(pointerIndex);
x = (int) event.getX(pointerIndex);
y = (int) event.getY(pointerIndex);
if (event.getPointerCount() > 1)
{
pointerIndex2 = pointerIndex== 0 ? 1 : 0;
x2 = (int)event.getX(pointerIndex2);
y2 = (int)event.getY(pointerIndex2);
}
}
If you''re tracking more points, or need more information about each touchevent, you have to extend the for loop up over the action switch case.
Anyway, now you need two variables in your thread so you can keep track of your two touches: call 'em touchOneID and touchTwoID (or index). On an ACTION_POINTER_2_UP, the obj.mPointerID refers to the obj which is going UP! This means that the other touch will change it's ID! Keep track of this change, and you're sorted. The internal obj's mPointerID/Index will always be correct, you just have to track them correctly in your surfaceview's thread so you can act accordingly to when you get a POINTER_DOWN. In my case, I did a simple x position check to determine what to do in my ACTION_MOVE event which told me enough to correctly determine which x/y or x2/y2 I should use and how to use it. This meant less code to run and limits to the things I had to keep in memory, but it all depends on what and how much information you need.
Finally:
To be honest, if you handled the definitions correctly and assigned every MotionEvent and held them in the InputObject, you'd probably be fine. Hell, I think you can ignore and lose the whole switch case and just say obj.mAction = event.getAction() and handle these in your processInput(obj)!
Meaning, all those static ints he's remapping to in the InputHolder seem unnecessary, unless you really only need one or two touch definitions (which explains his mysterious standalone comment of "this app is only interested in down touches"). Getting rid of those statically defined ints also means you can just test against MotionEvent.ACTION_CODE instead of doing a lookup against InputHolder.TOUCH_ACTION_CODE.

detect move event by index pointer in android

I am working on a multitouch program that needs to record only the movements made by the second finger or index pointer.
Now the documentation says that we can use MotionEvent.ACTION_POINTER_INDEX_MASK and & it with action and shift by INDEX_SHIFT to get the pointer that made the action like going up or down. But this technique does not work on move.
Is there anyway that we can detect the move action made by a certain pointer alone?
Thx,
yes, you can have something like this in your View class:
#Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getActionMasked()) {
case MotionEvent.ACTION_MOVE:
if(event.getPointerCount()>1){
//where 1 is the index of the second finger
final int Y = event.getY(1);
final int X = event.getX(1);
}
break;
}
}
so depending on what finger you want to get the movent you can set the get to that index. Rember that values may be from 0 (the first pointer that is down) to getPointerCount()-1.
I tested this on 2.2 Gingerbread so I hope it be useful for you :)
You can get the effective pointer index by checking which pointer changed:
private final int MAX_POINTER = 5; // 5 different touch pointers supported on most devices
private float mLastTouchPositionX[];
private float mLastTouchPositionY[];
#Override
public boolean onTouchEvent(MotionEvent aEvent)
int tActionIndex = aEvent.getActionIndex();
int tPointerCount = aEvent.getPointerCount();
/*
* Check which pointer changed on move
*/
if (tMaskedAction == MotionEvent.ACTION_MOVE) {
for (int i = 0; i < tPointerCount && i < MAX_POINTER; i++) {
if (mLastTouchPositionX[i] != aEvent.getX(i) || mLastTouchPositionY[i] != aEvent.getY(i)) {
mLastTouchPositionX[i] = aEvent.getX(i);
mLastTouchPositionY[i] = aEvent.getY(i);
// Found new action index
tActionIndex = i;
break;
}
}
}
...
}

How to implement Drag and drop in ListView to another Listview?

I am implementing Drag and Drop from ListView to another ListView,i got sample app here,
How to Drag drop Listview item to another Listview
using above app created one app,It's working fine up to 4th image of ListView.In my view By default ListView display up to 3rd position(means 0,1,2,3),if i drag the 2nd position from first ListView and drop in second ListView,It's display same image.When i scroll down,positions is 4,5,6,7.if i drag 6th position,it's takes 2nd position. please help me
You should use a for loop .Then give the count of number to the list and check with each count.Check if the id's of the loops are the same if they are different you will directly get different images at the stored place.
public boolean onTouchEvent(MotionEvent ev) {
// TODO Auto-generated method stub
final int action = ev.getAction();
final int x = (int) ev.getX();
final int y = (int) ev.getY();
if (action == MotionEvent.ACTION_DOWN && x < this.getWidth()/4) {
mDragMode = true;
}
if (!mDragMode)
return super.onTouchEvent(ev);
switch (action) {
case MotionEvent.ACTION_DOWN:
mStartPosition = pointToPosition(x,y);
if (mStartPosition != INVALID_POSITION) {
int mItemPosition = mStartPosition - getFirstVisiblePosition();
mDragPointOffset = y - getChildAt(mItemPosition).getTop();
mDragPointOffset -= ((int)ev.getRawY()) - y;
startDrag(mItemPosition,y);
drag(0,y);// replace 0 with x if desired
}
break;
case MotionEvent.ACTION_MOVE:
drag(0,y);// replace 0 with x if desired
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
default:
mDragMode = false;
mEndPosition = pointToPosition(x,y);
stopDrag(mStartPosition - getFirstVisiblePosition());
if (mDropListener != null && mStartPosition != INVALID_POSITION && mEndPosition != INVALID_POSITION)
mDropListener.onDrop(mStartPosition, mEndPosition);
break;
}
return true;
}
this will help u to push the code in from one location to another.And on the Drag method specify the x&y where you want to push it.

GestureDetector with onItemLongclick

How can i integrate GestureDetector with onItemLongClick?
I have a GridView containing three images. When I touch on the first image, I want to display a Toast message. When I lift up my finger from the screen, I want to display a second Toast message.
I know that GestureDetector uses MotionEvent, but onItemLongClick does not. But in this case, I would need to keep track of the image's position ID in the grid, thus it is not possible to implement inside onTouch()?
You can track the motion of the cursor, whether its a onscreen touch or a TrackBall move, using this class and if it crosses over into the next picture you can handle that event then. Here is an example taken from the sdk examples:
#Override public boolean onTouchEvent(MotionEvent event) {
int action = event.getActionMasked();
if (action != MotionEvent.ACTION_UP && action != MotionEvent.ACTION_CANCEL) {
int N = event.getHistorySize();
int P = event.getPointerCount();
for (int i = 0; i < N; i++) {
for (int j = 0; j < P; j++) {
mCurX = event.getHistoricalX(j, i);
mCurY = event.getHistoricalY(j, i);
drawPoint(mCurX, mCurY,
event.getHistoricalPressure(j, i),
event.getHistoricalTouchMajor(j, i));
}
}
for (int j = 0; j < P; j++) {
mCurX = event.getX(j);
mCurY = event.getY(j);
drawPoint(mCurX, mCurY, event.getPressure(j), event.getTouchMajor(j));
}
}
return true;
}
You can read more and see the file in your SDK at C:\YourInstallDir\android-sdk\samples\android-10\ApiDemos\src\com\example\android\apis\graphics\TouchPaint.java or just search the whole examples files for MotionEvent there's a few more uses in them.

Multiple finger input for android development

After getting the calculator application to work I decided to try to create pong. There is a box in the center and two paddles on both ends. The phone is horizontal. I have the box bouncing off the walls and the paddle moves with me moving my finger down. My problem is i want to make it two player and i want to have multiple finger input for the game. I want one finger to move paddle 1 and the other to move paddle 2. So far this is my input code
#Override
public boolean onTouchEvent(MotionEvent ev) {
final int action = ev.getAction();
switch (action) {
case MotionEvent.ACTION_MOVE: {
// Find the index of the active pointer and fetch its position
float p1y = ev.getY();
if(ev.getX()<300)
{
player1y = p1y;
}
if(ev.getX()>300)
{
player2y = p1y;
}
//player1y = p1y;
invalidate();
break;
}
}
return true;
}
it resides in my surfaceview class. How can i modify the input method or completely get rid of it and change it to accomplish my goal? Also sorry about my variables. Eclipse crashes a lot on me and my laptops touch panel tends to move my cursor so shorter variables seemed viable. p1y is the y of the touch. and player1y and player2y is the y positions of the player1 and player2 paddle.
A MotionEvent can hold multiple pointers. Use getPointerCount() to see how many pointers are touching the screen in the current event. There are alternate versions of getX and getY that take an index from 0-getPointerCount() - 1.
In a more complex app you would want to track fingers by pointer ID, but for something this simple where you are using a cutoff point on the screen you could do something like this in your ACTION_MOVE case:
int pointerCount = ev.getPointerCount();
for (int i = 0; i < pointerCount; i++) {
float x = ev.getX(i);
float y = ev.getY(i);
if (x < 300) {
player1y = y;
} else if (x > 300) {
player2y = y;
}
}
This post from the Android Developers Blog might help if you'd like more information: http://android-developers.blogspot.com/2010/06/making-sense-of-multitouch.html

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