Xcode NSURLConnection NSMutableData appdendData有時只能起作用

Question

我有一個奇怪的問題，從api讀取響應。在connectionDidFinishLoading中，將響應記錄爲字符串[NSString stringWithUTF8String:[self.response bytes]]時，該字符串有時會被正確記錄，有時爲空，而其他時間是在末尾附加隨機字符的正確響應。

在didReceiveData中，響應很好，但是在使用appendData之後發生問題。在didReceiveData我可以說明這樣的問題：

// This is always 0 
NSLog(@"data length is %i", [data length]); 
// This is always the correct response string sent from the api 
NSLog(@"data string is %@", [NSString stringWithUTF8String:[data bytes]]); 

NSMutableData *foo = [[NSMutableData alloc] init]; 
[foo appendData:data]; 

// This is always 8 
NSLog(@"foo length is %i", [foo length]); 
// This is only sometimes the correct response string! 
NSLog(@"foo string is %@", [NSString stringWithUTF8String:[foo bytes]]); 

[foo release]; 
foo = nil; 

我已經看到了SO約類似瘋狂的問題appendData一對夫婦的其他問題，但他們似乎已經因爲變量被追加到幾乎等於零。這表明我已經清楚地聲明瞭我的NSMutableData foo，但它仍然沒有正確設置。

Answer 1

請發佈整個代碼，而不僅僅是這個簡短的摘錄。

我假設你正在重新分配一個新的NSMutableData實例每次-connection:didReceiveData:被調用。您需要使用屬性或iVar，以便在調用-connection:didReceiveData:後續時間時將數據附加到已存在的數據。

- (void)startConnection 
{ 
    self.receivedData = [[NSMutableData alloc] init]; 
    // Start connection... 
} 

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data 
{ 
    [self.receivedData appendData:data]; 
} 

- (void)connectionDidFinishLoading:(NSURLConnection *) 
{ 
    NSString *receivedString = [[NSString alloc] initWithData:self.receivedData encoding:NSUTF8StringEncoding]; 
    self.receivedData = nil; 

    NSLog(@"Response: %@", receivedString); 
}