IOS之UI异步刷新

NSOperationQueue     *operationQueue; // for rendering pages on second thread

[operationQueue waitUntilAllOperationsAreFinished];

一句很简单的代码，可以实现UI的异步操作，知道操作完成，才进行进一步刷新。

NSOperationQueue是一个Operation执行队列，你可以将任何你想要执行的Operation添加到Operation Queue中，以在队列中执行。同时Operation和Operation Queue提供了很多可配置选项。Operation Queue的实现中，创建了一个或多个可管理的线程，为队列中的Operation提供可高度自定的执行环境。

DemoCode如下：

// Don't change font feature settings until all secondary thread operations are done

[operationQueue waitUntilAllOperationsAreFinished];

// Set up our font feature bitfield for given optionName

ASDFeaturesBits optionBitSelected = 0;

if (([optionName rangeOfString:ASD_SMALL_CAPITALS]).length > 0 ) {

optionBitSelected = ASDFeaturesSmallCaps;

}

else if (([optionName rangeOfString:ASD_RARE_LIGATURES]).length > 0 ) {

optionBitSelected = ASDFeaturesLigatures;

}

else if (([optionName rangeOfString:ASD_PROP_NUMBERS]).length > 0 ) {

optionBitSelected = ASDFeaturesPropNumbers;

}

else if (([optionName rangeOfString:ASD_STYLISTIC_VARS]).length > 0 ) {

optionBitSelected = ASDFeaturesStylisticVariants;

}

if (optionBitSelected && ((optionBitSelected & ASDFeaturesFeatureMask) != 0)) {

// Font features are most of the time exclusive so for simplicity we allow one feature at a time

viewOptions &= ~ASDFeaturesFeatureMask;

viewOptions |= optionBitSelected;

}

else {

// Passing @"" as the option is used to turn off all options

if ([optionName length] == 0) {

viewOptions = 0;

} else {

viewOptions ^= optionBitSelected;

}

}

if (pageViews[currCoreTextView].selectedFrame == NSUIntegerMax) {

// No selected frame, apply font features to all doc text

NSRange range = NSMakeRange(0, [document.attributedString length]);

[document setFontFeatures:(viewOptions & CoreTextViewOptionsFeatureMask) range:range];

[self relayoutDocFromPage:pageDisplayed];

}

else {

// Apply font features to selected frame

// (note that this only applies for "text" type frames)

CoreTextViewPageInfo* page = [pagesInfo objectForKey:[NSNumber numberWithInt:pageDisplayed]];

CoreTextViewFrameInfo* frame = [page.framesToDraw objectAtIndex:pageViews[currCoreTextView].selectedFrame];

if (frame.frameType == ASDFrameTypeTextFlow) {

[document setFontFeatures:(viewOptions & CoreTextViewOptionsFeatureMask) range:frame.stringRange];

[self relayoutDocFromPage:pageDisplayed];

}

else if (frame.frameType == ASDFrameTypeText) {

ApplyFontFeaturesToString(frame.value, frame.stringRange, (viewOptions & CoreTextViewOptionsFeatureMask));

[frame refreshTextFrame];

[self refreshPage];

}

}