Question

Just a quick question to confirm the documentation:

The getY(int) function from MotionEvent in the Android confuses me with its documentation:

Returns the Y coordinate of this event for the given pointer index (use getPointerId(int) to find the pointer identifier for this index). Whole numbers are pixels; the value may have a fraction for input devices that are sub-pixel precise.

With that I thought that the code should be written like this:

for(int i = 0; i < event.getPointerCount(); ++i) {
    // Some code...
    int currentPointer = event.getPointerId(i);
    float currentY = event.getY(currentPointer);
    Log.i("test", "Pointer " + currentPointer + " has Y-coord of " + currentY);
    // Some more code ...
}

However, in testing on my Samsung Galaxy Tab it appears that I should not pass currentPointer into getY but rather just the ‘i’ like so:

for(int i = 0; i < event.getPointerCount(); ++i) {
    // Some code...
    int currentPointer = event.getPointerId(i);
    float currentY = event.getY(i);
    Log.i("test", "Pointer " + currentPointer + " has Y-coord of " + currentY);
    // Some more code ...
}

Is that the correct way of using the getPointerId and getY functions? You give them the both the same ‘i’ variable and never their actual pointer id’s?

I am asking because I want to make sure that this is not different on just my device and this is indeed the way that it is intended to work. Thanks.

Answer 1

Yes, it’s correct, you should specify only “i”.

All the getPointer*(int) methods take the same index as parameter.