刚才我在Facebook上看到this announcement关于IOS的螺栓框架。
我可以将其视为主要概念：
Bolts中的第一个组件是“任务”，它使复杂异步代码的组织更易于管理
但我没有得到这个。我对Bolts framework感到困惑。如何使用它（ whether its related to web service or to JSON response parsing ）。
他们提供了带有解析SDK的ParseObject示例，但我不知道它，并且他们没有提供Xcode项目的任何示例。
Facebook就此提供了explanation。但我无法弄清楚如何与我的项目整合。
他们提供的代码非常令人困惑：
[[object saveAsync:obj] continueWithBlock:^id(BFTask *task) {
if (task.isCancelled) {
// the save was cancelled.
} else if (task.error) {
// the save failed.
} else {
// the object was saved successfully.
SaveResult *saveResult = task.result;
}
return nil;
}];
我们可以下载bolt-framework here。任何人都可以解释一下这个吗？
更新： Here我收到了一些关于螺栓新问题的答案。
示例： 假设您要加载AssertLibrary中的所有图像并在加载时将所有图像调整为标准大小，因此如果使用主线程，则会触发。在这个地方，如果你采用异步操作方式，如何使用BFTask呢？另一个例子。有一段时间，你试图用异步操作并行调用10个webservice，你怎么能在BFTask中使用GCD？
答案 0 :(得分：10)
螺栓很棒。同意文档现在有点不重要。不过，这是一个简单的例子：
// the completion source is the *source* of the task...
BFTaskCompletionSource *source = [BFTaskCompletionSource taskCompletionSource];
[self asynchronousMethodWithCompletion:^(id response, NSError *error) {
// your task completed; inform the completion source, which handles
// the *completion* of the task
error ? [source setError:error] : [source setResult:entity];
}];
[source.task continueWithBlock:^id(BFTask *task) {
// this will be executed after the asynchronous task completes...
}];
我发现它对组完成（半伪代码）特别有用：
NSMutableArray *tasks = @[].mutableCopy;
loop {
BFTaskCompletionSource *source = [BFTaskCompletionSource taskCompletionSource];
// ...make a task similar to above...
[tasks addObject:source.task];
}
// now the group completion:
BFTask *groupTask = [BFTask taskForCompletionOfAllTasks:tasks.copy];
[source.task continueWithBlock:^id(BFTask *task) {
// this will be executed after *all* the group tasks have completed
}];
这是一种更简洁的方式，可以执行您可能对调度组执行的操作。不过，在串行和并行等方面对任务进行排序等方面还有很多其他方法。
希望能帮助您入门。
答案 1 :(得分：0)
这是一个应用程序的完整示例，可以支持多个参与者在处理网络请求和用户交互时更改数据。
我为自己设定了一个指导原则，在触及与线程安全相关的任何服务时，使用链接到序列dispatch_queue_t的BFExecutor。
指出其他最佳做法会很有用，谢谢！
#import <Bolts/Bolts.h>
dispatch_queue_t serialQueue;
BFExecutor *serialExecutor;
BFTask *maintask;
int32_t key = 0;
BOOL initialized = FALSE;
@implementation yAppDelegate
- (void)setKey:(int32_t)key_ {
// Don't worry about success, just appending to outstanding tasks
maintask = [maintask continueWithExecutor:serialExecutor withBlock:^id(BFTask *task) {
BFTaskCompletionSource *source = [BFTaskCompletionSource taskCompletionSource];
key = key_;
NSLog(@"set key to %d", key);
[source setResult:nil];
if (initialized) {
[self initialize];
}
return source.task;
}];
}
- (BFTask *)downloadConfig {
BFTaskCompletionSource *source = [BFTaskCompletionSource taskCompletionSource];
dispatch_async(serialQueue, ^{
NSLog(@"working on init config, key = %d...", key);
// Trigger from a different queue
double delayInSeconds = 1.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
[source setResult:nil];
});
});
return source.task;
}
- (BFTask *)initializeService {
BFTaskCompletionSource *source = [BFTaskCompletionSource taskCompletionSource];
dispatch_async(serialQueue, ^{
NSLog(@"working on init service, key = %d...", key);
// Trigger from a different queue
double delayInSeconds = 1.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
[source setResult:nil];
});
// Set final state
initialized = TRUE;
});
return source.task;
}
- (void)initialize {
int32_t oldKey = key;
__block bool reinit = false;
// Start by chaining it to whatever task is in flight without regard to success
// Everything should use the serialQueue or serialExecutor for thread safety
maintask = [[[maintask continueWithExecutor:serialExecutor withBlock:^id(BFTask *task) {
if (oldKey != key) {
NSLog(@"key out of date (%d != %d). reinitializing...", oldKey, key);
reinit = true;
return [BFTask cancelledTask];
}
return [self downloadConfig];
}] continueWithExecutor:serialExecutor withSuccessBlock:^id(BFTask *task) {
if (oldKey != key) {
NSLog(@"key out of date (%d != %d). reinitializing...", oldKey, key);
reinit = true;
return [BFTask cancelledTask];
}
return [self initializeService];
}] continueWithExecutor:serialExecutor withBlock:^id(BFTask *task) {
if (oldKey != key) {
NSLog(@"key out of date (%d != %d). reinitializing...", oldKey, key);
reinit = true;
}
if (task.error || task.exception || task.isCancelled) {
if (reinit) {
[self initialize];
}
return nil;
} else {
NSLog(@"initService completed = %d", key);
return nil;
}
}];
}
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
serialQueue = dispatch_queue_create("serial", NULL);
serialExecutor = [BFExecutor executorWithDispatchQueue:serialQueue];
// Start with an empty task so all tasks can be strung together without need to initialize
maintask = [BFTask taskWithResult:nil];
// Everything related to changing service state should be contained with the serialQueue dispatch queue
[self setKey:1];
[self initialize];
[self setKey:2];
[self setKey:3];
dispatch_async(dispatch_get_main_queue(), ^(void){
[self setKey:4];
});
dispatch_async(serialQueue, ^(void){
[self setKey:5];
});
[self setKey:6];
// Override point for customization after application launch.
return YES;
}
@end
结果如预期。尝试使用key = 1进行初始化，但是在它停止更改之前是不同的。然后使用key = 5在其队列上初始化该服务，然后使用key = 4重新初始化。
<强>结果：
set key to 1
key out of date (0 != 1). reinitializing...
key out of date (0 != 1). reinitializing...
set key to 2
set key to 3
set key to 6
set key to 5
key out of date (1 != 5). reinitializing...
key out of date (1 != 5). reinitializing...
working on init config, key = 5...
working on init service, key = 5...
initService completed = 5
set key to 4
working on init config, key = 4...
working on init service, key = 4...
initService completed = 4
答案 2 :(得分：0)
请参阅测试文件（即TaskTests.m）以获取示例。 Github上的例子特定于Parse。
通常，查看为软件编写的测试就足以学习如何使用代码。