关于NSOperation的使用之一

//  QTileDownloadOperation.h
#import <Foundation/Foundation.h>

@interface QTileDownloadOperation : NSOperation

@property(nonatomic, retain)NSString* name;

- (void)clear;

@end

//  QTileDownloadOperation.m
#import "QTileDownloadOperation.h"

@implementation QTileDownloadOperation
@synthesize name;

- (void)dealloc {
    [name release];

    //......
    [super dealloc];
}


- (void)main
{
    if ([self isCancelled] || [self isFinished]) {
        return;
    }

    NSLog(@"%@start!",name);
    NSString* urlString = [@"你得URL" stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

    NSURL* url = [NSURL URLWithString:urlString];
    NSMutableURLRequest* requestWithAgent = [NSMutableURLRequest requestWithURL:url];

    [requestWithAgent setValue:@"mapapi" forHTTPHeaderField:@"User-Agent"];
    [requestWithAgent setTimeoutInterval:120];

    NSError* error = nil;

    NSData *data = [NSURLConnection sendSynchronousRequest:requestWithAgent returningResponse:nil error:&error];

    if (error == nil) {

        if (![self isCancelled])
        {
            [self didFinishWithData:data];
        }
    }
    else
    {
       //error handle
       //对外通知，注意线程同步
    }
}

- (void)didFinishWithData:(NSData*)data
{
    NSLog(@"%@complete!",name);
    //数据处理.........................
    //对外通知，注意线程同步
}

- (void)clear
{
    //可以进行取消网络，delegate置为nil,清理其他资源等。主要是防止线程对象释放时Crash
}

@end

NSOperationQueue* q = [[NSOperationQueue alloc] init];
self.myQueue = q;
//设置允许最大并发数
[myQueue setMaxConcurrentOperationCount:2];
[q release];

for (int i = 0; i < 8; ++i) {

    QTileDownloadOperation* op = [[QTileDownloadOperation alloc] init];
    NSString* name = [NSString stringWithFormat:@"op%d",i];
    op.name = name;
    [myQueue addOperation:op];
    [op release];
}

NSArray *allOperations = [myQueue operations];

for (QTileDownloadOperation* op in allOperations) {

    if(![op isCancelled])
    {
        [op clear];
        [op cancel];
    }
}

[myQueue release];
myQueue = nil;

NSArray *allOperations = [myQueue operations];
for (int i = [myQueue maxConcurrentOperationCount];  i < [allOperations count]; ++i) {
    QTileDownloadOperation* op = [allOperations objectAtIndex:i];

    if (!op.isCancelled) {

        [op clear];
        [op cancel];
    }
}