问题
I'm currently fiddling around with Android programming, but I have a small problem detecting different touch events, namely a normal touch press (press on the screen and release right away), a long press (touch the screen and hold the finger on it) and movement (dragging on the screen).
What I wanted to do is have an image (of a circle) on my screen which I can drag around. Then when I press it once (short/normal press) a Toast comes up with some basic information about it. When I long press it, an AlertDialog with a list comes up to select a different image (circle, rectangle or triangle).
I made a custom View with my own OnTouchListener to detect the events and draw the image in onDraw. The OnTouchListener.onTouch goes something like this:
// has a touch press started?
private boolean touchStarted = false;
// co-ordinates of image
private int x, y;
public boolean onTouch(View v, MotionEvent event) {
int action = event.getAction();
if (action == MotionEvent.ACTION_DOWN) {
touchStarted = true;
}
else if (action == MotionEvent.ACTION_MOVE) {
// movement: cancel the touch press
touchStarted = false;
x = event.getX();
y = event.getY();
invalidate(); // request draw
}
else if (action == MotionEvent.ACTION_UP) {
if (touchStarted) {
// touch press complete, show toast
Toast.makeText(v.getContext(), "Coords: " + x + ", " + y, 1000).show();
}
}
return true;
}
The problem is that the press doesn't quite work as expected, because when I casually touch the screen it also detects a tiny bit of movement and cancels the touch press and moves around the image instead.
I "hacked" around this a bit my introducing a new variable "mTouchDelay" which I set to 0 on ACTION_DOWN, increase in MOVE and if it's >= 3 in MOVE I execute my "move" code. But I have a feeling this isn't really the way to go.
I also haven't found out how to detect a long press. The culprit really is the MOVE which seems to always trigger.
For an example of what I roughly want, see the Android application "DailyStrip": it shows an image of a comic strip. You can drag it if it's too large for the screen. You can tap it once for some controls to pop-up and long press it for an options menu.
PS. I'm trying to get it to work on Android 1.5, since my phone only runs on 1.5.
回答1:
This code can distinguish between click and movement (drag, scroll). In onTouchEvent set a flag isOnClick, and initial X, Y coordinates on ACTION_DOWN. Clear the flag on ACTION_MOVE (minding that unintentional movement is often detected which can be solved with a THRESHOLD const).
private float mDownX;
private float mDownY;
private final float SCROLL_THRESHOLD = 10;
private boolean isOnClick;
@Override
public boolean onTouchEvent(MotionEvent ev) {
switch (ev.getAction() & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN:
mDownX = ev.getX();
mDownY = ev.getY();
isOnClick = true;
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
if (isOnClick) {
Log.i(LOG_TAG, "onClick ");
//TODO onClick code
}
break;
case MotionEvent.ACTION_MOVE:
if (isOnClick && (Math.abs(mDownX - ev.getX()) > SCROLL_THRESHOLD || Math.abs(mDownY - ev.getY()) > SCROLL_THRESHOLD)) {
Log.i(LOG_TAG, "movement detected");
isOnClick = false;
}
break;
default:
break;
}
return true;
}
For LongPress as suggested above, GestureDetector is the way to go. Check this Q&A:
Detecting a long press with Android
回答2:
From the Android Docs -
onLongClick()
From View.OnLongClickListener. This is called when the user either touches and holds the item (when in touch mode), or focuses upon the item with the navigation-keys or trackball and presses and holds the suitable "enter" key or presses and holds down on the trackball (for one second).
onTouch()
From View.OnTouchListener. This is called when the user performs an action qualified as a touch event, including a press, a release, or any movement gesture on the screen (within the bounds of the item).
As for the "moving happens even when I touch" I would set a delta and make sure the View has been moved by at least the delta before kicking in the movement code. If it hasn't been, kick off the touch code.
回答3:
I discovered this after a lot of experimentation.
In the initialisation of your activity:
setOnLongClickListener(new View.OnLongClickListener() {
public boolean onLongClick(View view) {
activity.openContextMenu(view);
return true; // avoid extra click events
}
});
setOnTouch(new View.OnTouchListener(){
public boolean onTouch(View v, MotionEvent e){
switch(e.getAction & MotionEvent.ACTION_MASK){
// do drag/gesture processing.
}
// you MUST return false for ACTION_DOWN and ACTION_UP, for long click to work
// you can return true for ACTION_MOVEs that you consume.
// DOWN/UP are needed by the long click timer.
// if you want, you can consume the UP if you have made a drag - so that after
// a long drag, no long-click is generated.
return false;
}
});
setLongClickable(true);
回答4:
I was looking for a similar solution and this is what I would suggest. In the OnTouch method, record the time for MotionEvent.ACTION_DOWN event and then for MotionEvent.ACTION_UP, record the time again. This way you can set your own threshold also. After experimenting few times you will know the max time in millis it would need to record a simple touch and you can use this in move or other method as you like.
Hope this helped. Please comment if you used a different method and solved your problem.
回答5:
If you need to distniguish between a click, longpress and a scroll use GestureDetector
Activity implements GestureDetector.OnGestureListener
then create detector in onCreate for example
mDetector = new GestureDetectorCompat(getActivity().getApplicationContext(),this);
then optionally setOnTouchListener on your View (for example webview) where
onTouch(View v, MotionEvent event) {
return mDetector.onTouchEvent(event);
}
and now you can use Override onScroll, onFling, showPress( detect long press) or onSingleTapUp (detect a click)
回答6:
I think you should implement GestureDetector.OnGestureListener as described in Using GestureDetector to detect Long Touch, Double Tap, Scroll or other touch events in Android and androidsnippets and then implement tap logic in onSingleTapUp and move logic in onScroll events
回答7:
I was just dealing with this mess after wanting longclick to not end with a click event.
Here's what I did.
public boolean onLongClick(View arg0) {
Toast.makeText(getContext(), "long click", Toast.LENGTH_SHORT).show();
longClicked = true;
return false;
}
public void onClick(View arg0) {
if(!longClicked){
Toast.makeText(getContext(), "click", Toast.LENGTH_SHORT).show();
}
longClick = false; // sets the clickability enabled
}
boolean longClicked = false;
It's a bit of a hack but it works.
回答8:
it just needed a ontouch event in the overlay class. check this, it helped me
http://mirnauman.wordpress.com/2012/04/16/android-google-maps-tutorial-part-6-getting-the-location-that-is-touched/
回答9:
GestureDetector.SimpleOnGestureListener has methods to help in these 3 cases;
GestureDetector gestureDetector = new GestureDetector(context, new GestureDetector.SimpleOnGestureListener() {
//for single click event.
@Override
public boolean onSingleTapUp(MotionEvent motionEvent) {
return true;
}
//for detecting a press event. Code for drag can be added here.
@Override
public void onShowPress(MotionEvent e) {
View child = recyclerView.findChildViewUnder(e.getX(), e.getY());
ClipboardManager clipboardManager = (ClipboardManager) context.getSystemService(Context.CLIPBOARD_SERVICE);
ClipData clipData = ClipData.newPlainText("..", "...");
clipboardManager.setPrimaryClip(clipData);
ConceptDragShadowBuilder dragShadowBuilder = new CustomDragShadowBuilder(child);
// drag child view.
child.startDrag(clipData, dragShadowBuilder, child, 0);
}
//for detecting longpress event
@Override
public void onLongPress(MotionEvent e) {
super.onLongPress(e);
}
});
来源：https://stackoverflow.com/questions/4324362/detect-touch-press-vs-long-press-vs-movement