ios - NSMakeRange导致应用程序锁定；表现慢

Question

我有一个困境，我认为到目前为止我能解决的很好。但是，当我使用UITableView测试它时，会收到各种警告，例如:

[__NSCFString substringWithRange:]: Range {2147483647, 2147483701} out of bounds; string length 56. This will become an exception for apps linked after 10.9. Warning shown once per app execution.

在下面发布方法之前，我将描述我要做的事情。基本上，当用户上传个人资料照片时，我在其用户名之后但在文件扩展名(.png)之前设置了唯一的子字符串，例如:JohnDoe的用户名拍摄了新的个人资料照片，我将文件名设置为:

NSString *file = [NSString stringWithFormat:@"JohnDoe%@.png",[[NSProcessInfo processInfo] globallyUniqueString]];

我这样做是为了让应用程序可以稍后查看是否需要下载用户 friend 的新个人资料图片，这是基于查看此完整的NSString是否保存在本地磁盘上，如果我找不到它保存在本地磁盘上，我只需从网络。问题很可能来自UITableView连续调用该方法。

另外，这需要在客户端完成，因此请不要讨论与后端相关的解决方案。

这是我想出的用于获取用户个人资料图像文件名的实际唯一NSString的方法。我的这种方法在- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath方法中调用

- (NSString *)actualPhotoPath:(NSDictionary *)input
{
    // This code needs work, ridiculous bottle neck!
    NSRange r1 = [[input objectForKey:@"pic"] rangeOfString:[input objectForKey:@"username"]];
    NSRange r2 = [[input objectForKey:@"pic"] rangeOfString:@".png"];
    NSRange rSub = NSMakeRange(r1.location + r1.length, r2.location - r1.location - r1.length);
    // Hangs up on the below line of code eventually
    NSString *sub = [[input objectForKey:@"pic"] substringWithRange:rSub];
    NSString *actual = [NSString stringWithFormat:@"%@%@.png",[input objectForKey:@"username"],sub];
    NSLog(@"%@",actual);
    return actual;
}

感谢您提供的任何帮助!谢谢

Answer 1

您应该检查if(r1.location != NSNotFound)和if(r2.location != NSNotFound)214748364710 == 0x7FFFFFFF16等于231-1，它是32位系统上的最高NSInteger值，也称为NSIntegerMax。
看看docs:

enum {
   NSNotFound = NSIntegerMax
};

- (NSString *)actualPhotoPath:(NSDictionary *)input
{
    NSRange r1 = [[input objectForKey:@"pic"] rangeOfString:[input objectForKey:@"username"]];
    NSRange r2 = [[input objectForKey:@"pic"] rangeOfString:@".png"];

    if(r1.location != NSNotFound && r2.location != NSNotFound){
        NSRange rSub = NSMakeRange(r1.location + r1.length, r2.location - r1.location - r1.length);
    
        NSString *sub = [[input objectForKey:@"pic"] substringWithRange:rSub];
        NSString *actual = [NSString stringWithFormat:@"%@%@.png",[input objectForKey:@"username"],sub];
        NSLog(@"%@",actual);
        return actual;
    }

    // if the code reaches this block, one of the ranges didn't work.
    // do what ever must be done in that case here
    return nil;
}

实际上，您首先应该创建r1，如果location!= NSFound，则应该使用r2的位置来确保在其后找到字符串png。

- (NSString *)actualPhotoPath:(NSDictionary *)input
{
    NSRange r1 = [[input objectForKey:@"pic"] rangeOfString:[input objectForKey:@"username"]];
    if (r1.location != NSNotFound ) {
        NSRange r2 = [[[input objectForKey:@"pic"] substringFromIndex:r1.location] rangeOfString:@".png"];
        
        if(r2.location != NSNotFound){
            NSRange rSub = NSMakeRange(r1.location + r1.length, r2.location - r1.location - r1.length);
            
            NSString *sub = [[input objectForKey:@"pic"] substringWithRange:rSub];
            NSString *actual = [NSString stringWithFormat:@"%@%@.png",[input objectForKey:@"username"],sub];
            NSLog(@"%@",actual);
            return actual;
        }
    }
    return nil;
}

或者，您可以使用NSRegularExpressions或NSScanner。