执行许多阻止主线程的UIKit操作

Question

when the app is launched, I'm programmatically creating many complex UIViews with transparent background colour, each being a 'screen' in the app (has to be this way since there's animated background underneath). This causes the app to stay on the static launch image for quite long (about 4 seconds).

I would like to create all the UIViews while an animation is shown. I can't create UIViews on background thread. How can I accomplish this?

Attempt 1:

-(void)viewDidLoad {

    [super viewDidLoad];


    dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        UIView *baseView = [[UIView alloc] initWithFrame:CGRectMake(20, 20, 200, 100)];
        [baseView setBackgroundColor:[UIColor blueColor]];

        UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(10, 10, 180, 80)];
        [button setBackgroundColor:[UIColor redColor]];
        [button setTitle:@"button" forState:UIControlStateNormal]; //doesn't work
        [baseView addSubview:button];

        dispatch_async( dispatch_get_main_queue(), ^{ //Finished

            [self.view addSubview:baseView];
        });

    });
}

The button is added, but the title is never set. It appears after tapped.

Answer 1

UIViews are not thread safe in normal usage, and all interaction should occur on the main thread. That said, you should be able to, on some background thread (dispatch queue), create the view, modify its parameters, set complex background colors, etc - as long as the view is not connected to anything (and thus receiving events from iOS). Once the view is completely setup and wired, then dispatch a block with it to the main queue and only then add it as a subview to some other view.

What I would do is dispatch all this work to the normal priority queue after having set up my initial video clip. When all the views have been posted back to the main queue (and thus this work is complete), you can stop the video and start interacting with the user.

Answer 2

Thanks for help. Here's the final solution that I tested and works perfectly.

I created a task manager class, FCTaskManager:

//Header File

typedef void (^TaskBlock)(void);
typedef void (^TaskCompletedBlock)(void);

@interface FCTaskManager : NSObject

-(void)performUITask:(TaskBlock)taskBlock completionBlock:(TaskCompletedBlock)taskCompletedBlock;
-(void)performBackgroundTask:(TaskBlock)taskBlock completionBlock:(TaskCompletedBlock)taskCompletedBlock;

@end



//Implementation

#import "FCTaskManager.h"

@implementation FCTaskManager

-(void)performUITask:(TaskBlock)taskBlock completionBlock:(TaskCompletedBlock)taskCompletedBlock {

    dispatch_async( dispatch_get_main_queue(), ^{

        @autoreleasepool {

            taskBlock();

            dispatch_async( dispatch_get_main_queue(), ^{

                taskCompletedBlock();
            });
        }
    });
}

-(void)performBackgroundTask:(TaskBlock)taskBlock completionBlock:(TaskCompletedBlock)taskCompletedBlock {

    dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        @autoreleasepool {

            taskBlock();

            dispatch_async( dispatch_get_main_queue(), ^{

                taskCompletedBlock();
            });
        }
    });
}

@end

Then I can use the task manager like so:

-(void)viewDidLoad {

    [super viewDidLoad];

    //Create taskManager
    taskManager = [[FCTaskManager alloc] init];

    //Create UIViews, etc WITHOUT blocking main queue
    [taskManager performUITask:^{

        button = [[UIButton alloc] initWithFrame:CGRectMake(30, 30, 300, 300)];
        [button setBackgroundColor:[UIColor redColor]];
        [button setTitle:@"Working" forState:UIControlStateNormal];
        [button addTarget:self action:@selector(buttonAction) forControlEvents:UIControlEventTouchUpInside];

    } completionBlock:^{

        NSLog(@"CREATED BUTTON");

        [self.view addSubview:button];
    }];
}