ios - Shouldn't KVO work syncronously? -

ios - Shouldn't KVO work syncronously? -

there must not getting kvo, trying scroll uitableview scrolling uiscrollview, offset translations right uitableview scrolling occurs after uiscrollview has finished scrolling.

here observing code:

- (void)observevalueforkeypath:(nsstring *)keypath ofobject:(id)object change:(nsdictionary *)change context:(void *)context { ailog(@"observevalueforkeypath:%@ ofobject:%@", keypath, nsstringfromclass([object class])); static bool isobservingcontentoffsetchange = no; if ([keypath isequaltostring:@"contentoffset"]) { if ([object isequal:self.scrollview]) { if (isobservingcontentoffsetchange) { return; } isobservingcontentoffsetchange = yes; cgpoint offset = [[change valueforkey:nskeyvaluechangenewkey] cgpointvalue]; nsdate *offsetday = [self dayforscrollviewoffset:offset]; if (offsetday) { ailog(@"offset (%.2f, %.2f)", offset.x, offset.y); ailog(@"offsetday %@", [df stringfromdate:offsetday]); nsindexpath *offsetindexpath = [self indexpathforday:offsetday]; ailog(@"offsetindexpath (%d, %d)", (int)offsetindexpath.section, (int)offsetindexpath.row); if (offsetindexpath) { cgrect rect = [self.tableview rectforsection:offsetindexpath.section]; [self.tableview setcontentoffset:cgpointmake(0, rect.origin.y) animated:yes]; ailog(@"----------------------------------------------"); } } else { ailog(@"nil offset day"); } } isobservingcontentoffsetchange = no; return; } [super observevalueforkeypath:keypath ofobject:object change:change context:context]; }

and here console log show working expected:

014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1526.50, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday sunday, 19/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (2, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1520.00, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday sunday, 19/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (2, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1514.00, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday sunday, 19/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (2, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1508.50, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday sunday, 19/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (2, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1503.50, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday sunday, 19/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (2, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1498.00, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday sunday, 19/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (2, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1493.00, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday sunday, 19/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (2, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1488.00, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday sunday, 19/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (2, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1483.50, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday saturday, 18/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (3, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1479.00, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday saturday, 18/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (3, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1474.50, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday saturday, 18/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (3, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1470.00, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday saturday, 18/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (3, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1466.00, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday saturday, 18/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (3, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1462.00, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday saturday, 18/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (3, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1458.50, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday saturday, 18/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (3, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1454.50, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday saturday, 18/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (3, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1450.50, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday saturday, 18/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (3, 0) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> ---------------------------------------------- 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> observevalueforkeypath:contentoffset ofobject:uiscrollview 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offset (1447.00, 0.00) 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetday saturday, 18/10/2014 2014-10-21 17:44:53 +0000 : bptimeviewcontroller --> offsetindexpath (3, 0)

but uitableview starts scrolling after content offsets calculation, when uiscrollview has finished decelerating (and there nil in uiscrollview delegate methods). know why so?

uitableview subclass of uiscrollview. when animate scrolling of uiscrollview, not utilize caanimation animate change, unlike other view animations. instead, uses timer.

i able reproduce problem , investigate. believe problem timer scheduled run in run loop's default mode (kcfrunloopdefaultmode), when user dragging scroll view (and when scroll view decelerating after drag), run loop in uitrackingrunloopmode. table view's scroll timer doesn't begin firing until deceleration ends.

there no documented (or otherwise obvious) way table view's timer run in other run loop modes, seems work:

[uiview animatewithduration:0.2 animations:^{ self.tableview.contentoffset = cgpointmake(0, rect.origin.y); }];

this worked me in simulator iphone 5 (7.0.3) , iphone 6 (8.0).

ios objective-c uitableview uiscrollview key-value-observing