iphone，如果我可以'在線程函數中填充，我該如何退出？

Question

我已將我的數據庫填充代碼添加到線程方法。但是，有時候他們可能沒有任何數據要顯示在圖表中。我不想運行查詢兩次，以前一次檢查是否有任何數據，並且我不想在線程函數之前預先填充圖形點。

我已經在下面標記了我的填充代碼。

我認爲我唯一的選擇是退出線程功能，但我有點擔心，我想正確地做到這一點，我需要做什麼？

#import "GraphController.h" 

@implementation GraphPoint 

- (id) initWithID:(int)pkv value:(NSNumber*)number{ 
    if(self = [super init]){ 
     pk = pkv; 
     value = [number retain]; 
    } 
    return self; 

} 

- (NSNumber*) yValue{ 
    return value; 
} 
- (NSString*) xLabel{ 
    return [NSString stringWithFormat:@"%d",pk]; 
} 
- (NSString*) yLabel{ 
    return [NSString stringWithFormat:@"%d",[value intValue]]; 
} 


@end 

@implementation GraphController 


- (void)viewDidLoad{ 
    [super viewDidLoad]; 

    graph.title.text = @"Graph View"; 

    [graph setPointDistance:15]; 

    indicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray]; 
    CGRect r = indicator.frame; 
    r.origin = self.view.bounds.origin; 
    r.origin.x = self.view.bounds.size.width/2 - r.size.width/2; 
    r.origin.y = self.view.bounds.size.height/2 - r.size.height/2; 
    indicator.frame = r; 
    [self.view addSubview:indicator]; 
    [indicator startAnimating]; 

    data = [[NSMutableArray alloc] init]; 

    [NSThread detachNewThreadSelector:@selector(thread) toTarget:self withObject:nil]; 

} 

- (void) thread{ 
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; 

//HERE 
    srand([[NSDate date] timeIntervalSince1970]); 

    for(int i=0;i<100;i++){ 
     int no = rand() % 100 + i; 
     GraphPoint *gp = [[GraphPoint alloc] initWithID:i value:[NSNumber numberWithFloat:no]]; 
     [data addObject:gp]; 
     [gp release]; 
    } 

    [self performSelectorOnMainThread:@selector(threadComplete) withObject:nil waitUntilDone:NO]; 

    [pool drain]; 
} 
- (void) threadComplete{ 
    [indicator stopAnimating]; 

    [self.graph setGraphWithDataPoints:data]; 
    self.graph.goalValue = [NSNumber numberWithFloat:30.0]; 
    self.graph.goalShown = YES; 
    [self.graph scrollToPoint:80 animated:YES]; 
    [self.graph showIndicatorForPoint:75]; 
} 

- (void)didReceiveMemoryWarning { 
    // Releases the view if it doesn't have a superview. 
    [super didReceiveMemoryWarning]; 

    // Release any cached data, images, etc that aren't in use. 
} 
- (void)viewDidUnload { 
    // Release any retained subviews of the main view. 
    // e.g. self.myOutlet = nil; 
} 
- (void)dealloc { 
    [data release]; 
    [indicator release]; 
    [super dealloc]; 
} 


@end 

我使用Tapku圖http://duivesteyn.net/2010/03/07/iphone-sdk-implementing-the-tapku-graph-in-your-application/?utm_source=twitterfeed&utm_medium=twitter

Answer 1

要關閉線程，從線程方法只是return。但是請不要忘記打電話給[pool release];（請在方法結束時使用它，而不要使用[pool drain];;在沒有GC的iOS上，它們是相同的，但如果Apple有一天決定添加GC支持，則它們是不同的）。

所以它是這樣的：

if (wantToCloseThread) { 
    // Release everything we've allocated. 
    [pool release]; 
    // Also, if you alloc'ed something that is not autoreleased 
    // you should release it here. 
    return; 
} 

另一種方法是使用goto（是的，它的這種用途是OK）：

- (void) thread { 

    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; 

    ... 

    if (something) 
     goto out; 

    ... 

    if (somethingElse) 
     goto out; 

    ... 

out: 
    // Cleanup. 
    [pool release]; 
    // Also, if you alloc'ed something that is not autoreleased 
    // you should release it here. 
} 

這樣，你必須編寫清理只有一次，goto確保每次你想離開線程時，完成清理工作。