On Dec 10, 2010, at 12:46 AM, fykcee1@gmail.com wrote:
2010/9/12 Dave Zarzycki <zarzycki@apple.com> On Sep 8, 2010, at 8:42 PM, cee1 wrote:
2. We have custom source of type DISPATCH_SOURCE_TYPE_DATA_ADD and DISPATCH_SOURCE_TYPE_DATA_OR, and can use dispatch_source_merge_data to fire custom sources. Why we don't have an 'is_level' source?
An "is_level" source may not make much sense, but can be attached with cancel handler, this may be useful in some cases.
If you can think of a practical use for that, then let us know.
I find a case, it's about adding T9 physical keyboard support on Android. We found some input methods already support T9 virtual keyboard but not physical one. So we handle onKeyDown event, translating a physical key press to a touch event on the virtual keyboard, e.g: key '2' -> touchEvent (10, 20) -- (10, 20) is (x,y) in screen coordinates.
Unfortunately synthesizing and sending a touch event will spend some time, causing android prompts not responsible of this program. So synthesizing and sending a touch event should be delayed to another thread. This time, 'is_level' custom source will be useful:
ds = dispatch_source_create(DISPATCH_SOURCE_TYPE_DATA_LEVEL, ...); dispatch_source_set_event_handler_f(ds, synthesize_and_send_touch_event);
onKeyDown() { dispatch_source_merge_data(ds, KEY_2); }
You would not want to implement a stream of keyboard events with an "is level" dispatch source. This is because users expect that keyboard events are not lossy, and a dispatch "is level" source would only tell your code what the last key press was, not the list of key presses that haven't been handled yet. A dispatch queue would be appropriate in this scenario. davez