[libdispatch-dev] Some questions about source handling

fykcee1 at gmail.com fykcee1 at gmail.com
Fri Dec 10 00:46:03 PST 2010

2010/9/12 Dave Zarzycki <zarzycki at 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);


- cee1
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