连接两个数组会导致null

Question

我试图将两个目录列表连接成一个数组，我得到目录数组以分别显示每个文件的列表（NSLog），但是通过addObjectsFromArray将它们连接在一起，结果为（null）：

NSString *path1 = [NSHomeDirectory() stringByAppendingPathComponent:@"Desktop/Dir1/"];
NSString *path2 = [NSHomeDirectory() stringByAppendingPathComponent:@"Desktop/Dir2/"];

NSArray *directoryList1 = [[[NSFileManager defaultManager] contentsOfDirectoryAtPath:path1 error:nil]
                                  pathsMatchingExtensions:[NSArray arrayWithObjects:@"log", nil]];

NSArray *directoryList2 = [[[NSFileManager defaultManager] contentsOfDirectoryAtPath:path2 error:nil]
                                  pathsMatchingExtensions:[NSArray arrayWithObjects:@"log", nil]];

NSLog(@"directoryList1 contains: %@", directoryList1);
NSLog(@"directoryList2 contains: %@", directoryList2);

NSMutableArray *directoryList;
[directoryList addObjectsFromArray:directoryList1];
[directoryList addObjectsFromArray:directoryList2];

NSLog(@"directoryList contains: %@", directoryList);

Answer 1

此：

NSMutableArray *directoryList;

定义指向数组的指针，但不创建实例。你应该：

NSMutableArray *directoryList = [NSMutableArray array];

所以你有东西可以添加内容。