Question

我是Objective-C编码的新手，请耐心问我这是否是一个简单的问题

我的页眉文件：

#import <Cocoa/Cocoa.h>

@interface AppDelegate : NSObject <NSApplicationDelegate>
@property (assign) IBOutlet NSWindow *window;

@end

我的实施档案：

#import "AppDelegate.h"

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{    
    // Insert code here to initialize your application

    // Listing 2-1  Creating a connection using NSURLConnection

    // Create the request.
    NSURLRequest *theRequest=[NSURLRequest requestWithURL:[NSURL    
                           URLWithString:@"http://www.apple.com/"]
                   cachePolicy:NSURLRequestUseProtocolCachePolicy
                                      timeoutInterval:60.0];

    // Create the NSMutableData to hold the received data.
    // receivedData is an instance variable declared elsewhere.
    receivedData = [NSMutableData dataWithCapacity: 0];

    // create the connection with the request
    // and start loading the data
    NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest              
           delegate:self];

    if (!theConnection) {
        // Release the receivedData object.
        receivedData = nil;

        // Inform the user that the connection failed.
    }
}

@end

在实施文件中的receivedData处显示未声明的标识符。如果在.h文件中声明该变量，则说明cannot declare variable inside @interface and protocol

Answer 1

正如您在评论中看到的那样：

// receivedData is an instance variable declared elsewhere.
receivedData = [NSMutableData dataWithCapacity: 0];

应该在某处声明receivedData。试试这个：

NSMutableData *receivedData = [NSMutableData dataWithCapacity: 0];

Answer 2

您必须在引用变量之前声明变量： NSMutableData* receivedData = [NSMutableData dataWithCapacity: 0];

使用未声明的标识符Objective-C代码

2 个答案: