調試主線程iPhone上的UI更新，活動指示器不旋轉

Question

所以我知道你應該在主線程上做你的更新。我使用蘋果的代碼寫我們的數據庫做文件目錄：

// Creates a writable copy of the bundled default database in the application Documents directory. 
- (void)createEditableCopyOfDatabaseIfNeeded { 
    // First, test for existence. 
    BOOL success; 
    NSFileManager *fileManager = [NSFileManager defaultManager]; 
    NSError *error; 
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
    NSString *documentsDirectory = [paths objectAtIndex:0]; 
    NSString *writableDBPath = [documentsDirectory stringByAppendingPathComponent:@"bookdb.sql"]; 
    success = [fileManager fileExistsAtPath:writableDBPath]; 
    if (success) 
     return; 
    // The writable database does not exist, so copy the default to the appropriate location. 
    NSString *defaultDBPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"bookdb.sql"]; 
    success = [fileManager copyItemAtPath:defaultDBPath toPath:writableDBPath error:&error]; 
    if (!success) { 
     NSAssert1(0, @"Failed to create writable database file with message '%@'.", [error localizedDescription]); 
    } 
} 

我做

[activityIndicator startAnimating]; 
[self createEditableCopyOfDatabaseIfNeeded]; 

我沒有看到我的活動指示燈。如果我註釋掉[self createEditableCopyOfDatabaseIfNeeded];，我確實看到了我的活動指標。有沒有一種方法來調試，看看發生了什麼，爲什麼我沒有看到我的旋轉指標？謝謝。

Answer 1

從上下文來看，很難說，但我假設您希望活動指示符代表createEditableCopyOfDatabaseIfNeeded正在進行的操作。假設你的主線程調用了[self createEditableCopyOfDatabaseIfNeeded]，你可以這樣做：

[activityIndicator startAnimating]; 
dispatch_async(dispatch_get_global_queue(0, 0), ^{ 
    [self createEditableCopyOfDatabaseIfNeeded]; 
    dispatch_async(dispatch_get_main_queue(), ^{ 
     [activityIndicator stopAnimating]; 
    }); 
});