iOS網路編程-ASIHTTPRequest非同步請求

我們運行程式，如果網速很慢，查詢的時候會一直黑屏，直到請求結束畫面才出現，這樣使用者體驗很不好。因此同步請求一般只是在某個子線 程中使用，而不在主線程中使用。非同步請求的使用者體驗要比同步請求好，因此一般情況下非同步請求用的很多。等待過程中在狀態列上會出現網路等待指標的經典旋 轉小表徵圖，而使用ASIHTTPRequest非同步請求就實現這些效果，不用自己額外編寫代碼。

 
 

ASIHTTPRequest和ASIFormDataRequest兩個請求類都可以發送非同步請求，ASIFormDataRequest繼承了 ASIHTTPRequest非同步要求方法，所以我們重點介紹ASIHTTPRequest的非同步請求。非同步請求後通過回調委派物件的方 法：requestFinished:和requestFailed:實現。修改主視圖控制器MasterViewController.m的 startRequest方法如下：

[cpp]
-(void)startRequest 
 
{ 
 
NSString *strURL = [[NSString alloc] 
 
initWithFormat: 
 
@”http://iosbook3/mynotes/webservice.php?email=%@&type=%@&action=%@”,  
 
@”<你的iosbook1.com使用者郵箱>”,@”JSON”,@”query”]; 
 
NSURL *url = [NSURL URLWithString:[strURL URLEncodedString]]; 
 
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url]; 
 
[request setDelegate:self];                                              ① 
 
[request startAsynchronous];                                              ② 
 
} 
 
- (void)requestFinished:(ASIHTTPRequest *)request                                ③ 
 
{ 
 
NSData *data  = [request responseData]; 
 
NSDictionary *resDict = [NSJSONSerialization 
 
JSONObjectWithData:data options:NSJSONReadingAllowFragments error:nil]; 
 
[self reloadView:resDict]; 
 
} 
 
- (void)requestFailed:(ASIHTTPRequest *)request                              ④ 
 
{ 
 
NSError *error = [request error]; 
 
NSLog(@”%@”, [error localizedDescription]); 
 
} 

-(void)startRequest

{

NSString *strURL = [[NSString alloc]

initWithFormat:

@”http://iosbook3/mynotes/webservice.php?email=%@&type=%@&action=%@”,

@”<你的iosbook1.com使用者郵箱>”,@”JSON”,@”query”];

NSURL *url = [NSURL URLWithString:[strURL URLEncodedString]];

ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];

[request setDelegate:self];                                              ①

[request startAsynchronous];                                              ②

}

- (void)requestFinished:(ASIHTTPRequest *)request                                ③

{

NSData *data  = [request responseData];

NSDictionary *resDict = [NSJSONSerialization

JSONObjectWithData:data options:NSJSONReadingAllowFragments error:nil];

[self reloadView:resDict];

}

- (void)requestFailed:(ASIHTTPRequest *)request                              ④

{

NSError *error = [request error];

NSLog(@”%@”, [error localizedDescription]);

}

第①行代碼[request setDelegate:self]設定委派物件為self，然後在第②行[request startAsynchronous]發起非同步請求，伺服器端返回成功則回調第③行的requestFinished:方法，失敗則回調第④行的 requestFailed:方法，它們的參數都是ASIHTTPRequest類型。這兩個方法是預設的回調方法，我們也可以自訂回調方法。因此上面 的代碼也可以改為如下形式：

[cpp]
-(void)startRequest 
 
{ 
 
… … 
 
    [request setDidFinishSelector:@selector(requestSuccess:)]; 
 
    [request setDidFailSelector:@selector(requestError:)]; 
 
[request startAsynchronous]; 
 
} 
 
- (void)requestSuccess:(ASIHTTPRequest *)request 
 
{ 
 
NSData *data  = [request responseData]; 
 
NSDictionary *resDict = [NSJSONSerialization JSONObjectWithData:data 
 
options:NSJSONReadingAllowFragments error:nil]; 
 
[self reloadView:resDict]; 
 
} 
 
- (void)requestError:(ASIHTTPRequest *)request 
 
{ 
 
NSError *error = [request error]; 
 
NSLog(@”%@”, [error localizedDescription]); 
 
} 

-(void)startRequest

{

… …

    [request setDidFinishSelector:@selector(requestSuccess:)];

    [request setDidFailSelector:@selector(requestError:)];

[request startAsynchronous];

}

- (void)requestSuccess:(ASIHTTPRequest *)request

{

NSData *data  = [request responseData];

NSDictionary *resDict = [NSJSONSerialization JSONObjectWithData:data

options:NSJSONReadingAllowFragments error:nil];

[self reloadView:resDict];

}

- (void)requestError:(ASIHTTPRequest *)request

{

NSError *error = [request error];

NSLog(@”%@”, [error localizedDescription]);

}

通過請求對象的setDidFinishSelector:方法指定要回調成功方法，setDidFailSelector:方法指定要回調的失敗方法。

在非同步請求中往往為了使代碼更加整潔可以使用代碼塊（Block），在代碼塊中指定回調方法。使用了代碼的主視圖控制器MasterViewController.m的startRequest方法如下：

[cpp]
-(void)startRequest 
 
{ 
 
NSString *strURL = [[NSString alloc] initWithFormat: 
 
@”http://iosbook3/mynotes/webservice.php?email=%@&type=%@&action=%@”,@”<你的iosbook1.com使用者郵箱>”,@”JSON”,@”query”];  
 
NSURL *url = [NSURL URLWithString:[strURL URLEncodedString]]; 
 
__weak ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];        ① 
 
[request setCompletionBlock:^{                                           ② 
 
NSData *data  = [request responseData];                               ③ 
 
NSDictionary *resDict = [NSJSONSerialization JSONObjectWithData:data 
 
options:NSJSONReadingAllowFragments error:nil]; 
 
[self reloadView:resDict]; 
 
}]; 
 
  
 
[request setFailedBlock:^{                                               ④ 
 
NSError *error = [request error]; 
 
NSLog(@”%@”, [error localizedDescription]); 
 
}]; 
 
[request startAsynchronous]; 
 
} 

-(void)startRequest

{

NSString *strURL = [[NSString alloc] initWithFormat:

@”http://iosbook3/mynotes/webservice.php?email=%@&type=%@&action=%@”,@”<你的iosbook1.com使用者郵箱>”,@”JSON”,@”query”];

NSURL *url = [NSURL URLWithString:[strURL URLEncodedString]];

__weak ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];        ①

[request setCompletionBlock:^{                                           ②

NSData *data  = [request responseData];                               ③

NSDictionary *resDict = [NSJSONSerialization JSONObjectWithData:data

options:NSJSONReadingAllowFragments error:nil];

[self reloadView:resDict];

}];

 

[request setFailedBlock:^{                                               ④

NSError *error = [request error];

NSLog(@”%@”, [error localizedDescription]);

}];

[request startAsynchronous];

}