StackOverflow2013

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copied!<p>To prevent touches from that layout you have several options:</p> <p>1) set OnTouchListener, which would always return true.</p> <p>2) override dispatchTouchEvent(MotionEvent event) to always return true</p> <p><strong>UPD:</strong> Okey, normally you would have to set OnTouchListener, which would always return true, as I said previously to prevent other views from being called <code>onTouch</code>, but with ScrollView it's completely another story.</p> <p>First of all I will tell how <code>dispatchTouchEvent</code> works. It starts dispatching event from the root view to it's child views, so that means that <code>dispatchTouchEvent</code> of parent is called <em>BEFORE</em> <code>dispatchTouchEvent</code> of it's children. </p> <p>Then in <code>ViewGroup.dispatchTouchEvent()</code> there is a piece of code </p> <pre><code>final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if (!disallowIntercept) { intercepted = onInterceptTouchEvent(ev); ev.setAction(action); // restore action in case it was changed } else { intercepted = false; } </code></pre> <p>which decides if this touch event should be intercepted, which means if <code>intercepted</code> flag is true, then this view would intercept all successive event. And in <code>ScrollView</code> <code>onInterceptTouchEvent</code> implemented to intercept actions if they are perfroming vertical scrolling.</p> <p>So my first idea was to set <code>FLAG_DISALLOW_INTERCEPT</code> to the parent of your custom view to disallow this opportunity of intercepting events, but this idea fails because of the next lines of code in <code>ViewGroup</code>:</p> <pre><code>if (actionMasked == MotionEvent.ACTION_DOWN) { // Throw away all previous state when starting a new touch gesture. // The framework may have dropped the up or cancel event for the previous gesture // due to an app switch, ANR, or some other state change. cancelAndClearTouchTargets(ev); resetTouchState(); } </code></pre> <p>So that means that after the <code>MotionEvent.ACTION_DOWN</code> all states are cleared (and so do <code>FLAG_DISALLOW_INTERCEPT</code> is also cleared).</p> <p>So the final solution is pretty simple</p> <pre><code>public class PreventingTouchEventView extends View { public PreventingTouchEventView(Context context, AttributeSet attrs) { super(context, attrs); } @Override protected void onDraw(Canvas canvas) { canvas.drawColor(Color.RED); } @Override public boolean dispatchTouchEvent(MotionEvent event) { if (getParent() != null && event.getAction() == MotionEvent.ACTION_DOWN) { getParent().requestDisallowInterceptTouchEvent(true); } return super.dispatchTouchEvent(event); } } </code></pre> <p>this would raise <code>FLAG_DISALLOW_INTERCEPT</code> right after first <code>MotionEvent.ACTION_DOWN</code>, which would dissallow further interception of future actions by parent. </p> <p>But note, that if your parent view doing some crazy stuff on <code>MotionEvent.ACTION_DOWN</code> and intercepting this event then you just can't do anything about it, because your parent's <code>dispatchTouchEvent</code> are called before your <code>dispatchTouchEvent</code>.</p>

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