Question

我正在做一些关于写入和加载文件的练习。

我创建了NSString，然后将其写入文件，然后再次加载NSString。简单。

如何使用NSMutableArray NSStrings或更好NSMutableArray我自己的班级来完成此操作？

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[])
{

    @autoreleasepool {

        // insert code here...

        //write a NSString to a file
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];
        NSString *filePath = [documentsDirectory stringByAppendingPathComponent:@"file.txt"];

        NSString *str = @"hello world";
        NSArray *myarray = [[NSArray alloc]initWithObjects:@"ola",@"alo",@"hello",@"hola", nil];

        [str writeToFile:filePath atomically:TRUE encoding:NSUTF8StringEncoding error:NULL];

        //load NSString from a file
        NSArray *paths2 = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory2 = [paths2 objectAtIndex:0];
        NSString *filePath2 = [documentsDirectory2 stringByAppendingPathComponent:@"file.txt"];
        NSString *str2 = [NSString stringWithContentsOfFile:filePath2 encoding:NSUTF8StringEncoding error:NULL];

        NSLog(@"str2: %@",str2);

    }
    return 0;
}

印刷：str2：你好世界

Answer 1

如果您想将数组编写为plist，可以

// save it

NSArray *myarray = @[@"ola",@"alo",@"hello",@"hola"];
BOOL success = [myarray writeToFile:path atomically:YES];
NSAssert(success, @"writeToFile failed");

// load it

NSArray *array2 = [NSArray arrayWithContentsOfFile:path];
NSAssert(array2, @"arrayWithContentsOfFile failed");

有关详细信息，请参阅属性列表编程指南中的Using Objective-C Methods to Read and Write Property-List Data。

但是，如果你想保留对象的可变性/不变性（即精确的对象类型），并且打开保存更多对象类型的可能性，你可能想要使用存档而不是一个plist：

NSMutableString *str = [NSMutableString stringWithString:@"hello world"];
NSMutableArray *myarray = [[NSMutableArray alloc] initWithObjects:str, @"alo", @"hello", @"hola", nil];

//save it

BOOL success = [NSKeyedArchiver archiveRootObject:myarray toFile:path];
NSAssert(success, @"archiveRootObject failed");

//load NSString from a file

NSMutableArray *array2 = [NSKeyedUnarchiver unarchiveObjectWithFile:path];
NSAssert(array2, @"unarchiveObjectWithFile failed");

虽然我用数组说明了这个技术，但它适用于任何符合NSCoding的对象（包括许多基本的Cocoa类，如字符串，数组，字典，NSNumber等）。。如果您想让自己的班级与NSKeyedArchiver一起使用，那么您也必须使它们符合NSCoding。有关详细信息，请参阅Archives and Serializations Programming Guide。

Answer 2

This document at Apple walks you through the process.

将NSMutableArray写入文件并加载回来

2 个答案: