NSString *urlStr = [NSString stringWithFormat:@"http://localhost/login.php?username=張三&password=1234"];
// 如果URL中包含中文字串或者特殊字元(例如空格)，需要給URL新增百分號轉義
urlStr = [urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

NSURL *url = [NSURL URLWithString:urlStr];

NSLog(@"urlStr:%@", urlStr);
// 列印結果：urlStr:http://localhost/login.php?username=%E5%BC%A0%E4%B8%89&password=1234

// 把經過百分號轉義的URL還原
urlStr = [@"http://localhost/login.php?username=%E5%BC%A0%E4%B8%89&password=1234" stringByRemovingPercentEncoding];

NSLog(@"urlStr:%@", urlStr);
// 列印結果：urlStr:http://localhost/login.php?username=張三&password=1234