1.獲取到對應的文件夾

+ (NSString *)getLogFilePath{
    NSString *documentsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    //log.txt文件
    documentsDir = [documentsDir stringByAppendingPathComponent:@"log.txt"];
    return documentsDir;
}

2.判斷對應文件是否存在，不存在則創(chuàng)建

    NSString *documentsDir = [self getLogFilePath];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    BOOL isExit = [fileManager fileExistsAtPath:documentsDir];
    //文件夾是否存在
    if (!isExit) {
        NSLog(@"log文件不存在");
        [fileManager createFileAtPath:documentsDir contents:nil attributes:nil];
    }

3.先讀取文件中數(shù)據(jù)，然后將全部數(shù)據(jù)寫入文件中

//先讀取文件中內(nèi)容
    NSError *error;
    NSString *content =[NSString stringWithContentsOfFile:documentsDir encoding:NSUTF8StringEncoding error:&error];
    if (!error) {
       NSLog(@"文件讀取成功: %@",content);
    }else{
       NSLog(@"%@",error.localizedDescription);
    }
    if (content.length == 0 || [content isKindOfClass:[NSNull class]] || content == nil) {
        NSLog(@"文件中無數(shù)據(jù)");
    }else{
        info = [NSString stringWithFormat:@"%@\n%@",content,info];
    }
    BOOL res = [info writeToFile:documentsDir atomically:YES encoding:NSUTF8StringEncoding error:nil];
    if (res) {
        NSLog(@"INFO寫入成功");
    }else {
        NSLog(@"INFO寫入失敗");
    }