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ezra heywood
ezra heywood

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Posted on    April-25-2015 8:18 AM

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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.



Mayank Tripathi
Mayank Tripathi

Total Post:397

Points:3117
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Posted on    April-25-2015 8:31 AM

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.

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);

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