基于网络的客户端开发技巧——第七篇后台上传

这里说的后台上传当然不是真的后台上传，只是在开启程序的情况下不影响操作的上传。

基本的思想就是开启一个线程，不断的处理上传操作。这里用队列比较方便一些。
主要做以下几步：

第一步：实现一个自定义类，继承NSObject
@interface MinroadOperation : NSObject {
NSOperationQueue *operationQueue;
}
- (void)addOperation:(NSDictionary *)_dic;
- (void)reStartOperation:(NSDictionary *)_dic;
@property (retain,nonatomic) NSOperationQueue *operationQueue;
@end

@implementation MinroadOperation
@synthesize operationQueue;
- (id)init
{
self = [super init];
if (self) {
self.operationQueue = [[NSOperationQueue alloc] init];
[self.operationQueue setMaxConcurrentOperationCount:2];//设置同时进行的线程数量，建议为2。
}
return self;
}

- (void)addOperation:(NSDictionary *)_dic
{
//保存上传列表到nsuserdefaults
NSUserDefaults *userDefault = [NSUserDefaults standardUserDefaults];
if ([userDefault valueForKey:@"upload"] == nil) {
NSMutableDictionary *dic = [NSMutableDictionary dictionaryWithObjectsAndKeys:[NSMutableArray arrayWithObject:_dic],@"upload",nil];
[userDefault registerDefaults:dic];
[userDefault synchronize];
}
else {
NSArray *array = [userDefault valueForKey:@"upload"];
NSMutableArray *arr = [[NSMutableArray alloc] initWithArray:array];
[arr addObject:_dic];
[userDefault setObject:arr forKey:@"upload"];
[arr release];
[userDefault synchronize];
}

//添加到队列
NSInvocationOperation* theOp = [[NSInvocationOperation alloc] initWithTarget:self
selector:@selector(myTaskMethod:) object:_dic];

[self.operationQueue addOperation:theOp];
[theOp release];

//更新UI
}

- (void)reStartOperation:(NSDictionary *)_dic
{
//从userdefaults读取数据，并添加到队列
NSUserDefaults *userDefault = [NSUserDefaults standardUserDefaults];
NSArray *array = [userDefault valueForKey:@"upload"];
NSMutableArray *arr = [[NSMutableArray alloc] initWithArray:array];
int i = (int)[arr indexOfObject:_dic];
if (i == NSNotFound) {
return;
}
NSMutableDictionary *dic = [NSMutableDictionary dictionaryWithDictionary:[arr objectAtIndex:i]];
[dic setValue:[NSNumber numberWithInt:0] forKey:@"state"];//0 等待上传 1 上传中 2 失败
[arr replaceObjectAtIndex:i withObject:dic];
[userDefault setValue:arr forKey:@"upload"];
[userDefault synchronize];

NSInvocationOperation* theOp = [[NSInvocationOperation alloc] initWithTarget:self
selector:@selector(myTaskMethod:) object:dic];

[self.operationQueue addOperation:theOp];
[theOp release];

//更新UI
}

- (void)myTaskMethod:(id)_obj
{
//实现上传方法
//成功调用
[self performSelectorOnMainThread:@selector(taskMethodDidFinish:) withObject:nil waitUntilDone:YES];
//失败调用
[self performSelectorOnMainThread:@selector(taskMethodDidFailed:) withObject:nil waitUntilDone:YES];
}

- (void)taskMethodDidFailed:(id)_obj
{
//失败的任务更改状态之后保存
NSDictionary *tdic = [_obj retain];

NSMutableDictionary *dic = [NSMutableDictionary dictionaryWithDictionary:tdic];
[dic setValue:[NSNumber numberWithInt:1] forKey:@"state"];

NSUserDefaults *userDefault = [NSUserDefaults standardUserDefaults];
NSArray *array = [userDefault valueForKey:@"upload"];
NSMutableArray *arr = [[NSMutableArray alloc] initWithArray:array];
int _index = (int)[arr indexOfObject:dic];
if (_index != NSNotFound) {
NSMutableDictionary *tmp = [NSMutableDictionary dictionaryWithDictionary:[arr objectAtIndex:_index]];
[tmp setValue:[NSNumber numberWithInt:2] forKey:@"state"];//0 等待上传 1 上传中 2 失败
[arr replaceObjectAtIndex:_index withObject:tmp];
}
[userDefault setObject:arr forKey:@"upload"];
[arr release];
[userDefault synchronize];

//更新UI
}

- (void)taskMethodDidFinish:(id)_obj
{
//成功的任务从userdefaults中删除
NSDictionary *tdic = [_obj retain];

NSMutableDictionary *dic = [NSMutableDictionary dictionaryWithDictionary:tdic];
[dic setValue:[NSNumber numberWithInt:1] forKey:@"state"];

NSUserDefaults *userDefault = [NSUserDefaults standardUserDefaults];
NSArray *array = [userDefault valueForKey:@"upload"];
NSMutableArray *arr = [[NSMutableArray alloc] initWithArray:array];
int _index = (int)[arr indexOfObject:dic];
if (_index != NSNotFound) {
[arr removeObjectAtIndex:_index];
}
[userDefault setObject:arr forKey:@"upload"];
[arr release];
[userDefault synchronize];

//更新UI
}

- (void)dealloc
{
[operationQueue release];
[super dealloc];
}
@end

第二步：在appdelegate中初始化一个MinroadOperation对象，添加的时候用addOperation(),重新开始的时候用reStartOperation()。

第三步：在程序重新开启的时候启动队列。同时有一点不确认，就是从后台返回貌似队列会继续进行，也就是说进入后台的时候队列处在等待状态。

需要注意的几点：
1. NSInvocationOperation的cancel方法只是设置一个标识，在进入队列的时候判断是否为true,从而判断是否进行。如果想取消NSInvocationOperation，可以尝试继承它。

2.避免无限重试。