Question

我正在使用返回大量数据的NsUrlConnection调用Web服务。这是多次调用didReceiveData方法，当我打印出来时，NSLog显示数据是正确的。

我遇到的问题现在与将didReceiveData方法中返回的NSData存储到NSMutableData ivar以供以后使用有关。

我在http://cagt.bu.edu/w/images/8/8b/URL_Connection_example.txt找到了一个使用它的示例，并进行了一些修改，我已经得到以下内容：

·H

@property (nonatomic,assign) NSMutableData *receivedData;

的.m

@synthesize receivedData;


-(Boolean) getCategories {

MCUtility * util = [MCUtility alloc];
NSString * strUrl = [NSString stringWithFormat:@"%@", [util getCategoryUrl]];
NSLog(@"%@", [NSString stringWithFormat:@"%@", strUrl]);

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:strUrl]];

[request setHTTPMethod:@"POST"];
[request setValue:@"application/x-www-form-urlencoded; charset=utf-8" forHTTPHeaderField:@"Content-Type"];

connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
if (connection == nil) {
    return FALSE;
} else {    
   self.receivedData = [NSMutableData data];
    [receivedData setLength:0]; //<<OK call
}

return TRUE;

}

#pragma NSURLCONNECTION

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
// This method is called when the server has determined that it
// has enough information to create the NSURLResponse object.

// It can be called multiple times, for example in the case of a
// redirect, so each time we reset the data.

// receivedData is an instance variable declared elsewhere.
if (receivedData != nil)
    [receivedData setLength:0]; //<< thread EXC_BAD_ACCESS (code 2, address....)
}


- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
NSLog(@"Data Received");
NSLog(@"%@", [NSString stringWithFormat:@"%@", [NSString stringWithUTF8String:[data bytes]]]);
[receivedData appendData:data];  //<< (2) thread EXC_BAD_ACCESS (code 2, address....)

在设置方法getCategories中，我使用

创建初始NSMutableData变量

self.receivedData = [NSMutableData data];

（（1）在此之后我添加了对[receivedData setLength：0]的测试调用;这实际上并不是代码的一部分，但在这里工作正常。）

对Web服务的调用很好，所以我开始在didReceiveData中接收数据。

在方法didReceiveResponse中，该示例声明了对[receivedData setLength：0]的调用;是必须的。此时我现在得到了一个

thread EXC_BAD_ACCESS (code 2, address....)

..我没有＆＃39;在我之前创建iVar对象之后就像我在（1）

中所说的那样得到这个错误

在方法didReceiveData中，当我尝试在（2）处将数据分配给NSMutableData时，我也收到此错误。

因此，作为一个客观的新手，我认为这与我用来存储数据的iVar有关。是否有任何简单明显的错过？

Answer 1

receivedData正在发布。

[NSMutableData data]返回一个自动释放的变量。您需要保留它或更改属性定义以保留它。

@property (nonatomic,retain) NSMutableData *receivedData;应该有用。

如果使用ARC，请将该属性设为

@property (nonatomic,strong) NSMutableData *receivedData;

NSURLCONNECTION didReceiveData：将NSDATA存储在NSMutableData错误中

1 个答案: