ios中各数据类型转换 NSData转NSString，Byte，UIImage

1，NSData 与 NSString

　　NSData --> NSString

　　NSString *aString = [[NSString alloc] initWithData:adata encoding:NSUTF8StringEncoding];

　　NSString --> NSData

　　NSString *aString = @"1234";

　　NSData *aData = [aString dataUsingEncoding: NSUTF8StringEncoding];

       特例：
               1、当我们使用消息推送时，通过AppDelegate的系统方法didRegisterForRemoteNotificationsWithDeviceToken获得的deviceToken为NSData类型的数据，但
                    是此处的NSData格式的数据是不能通过上面的方法转换的，我们可以通过这行代码实现转换：NSString
*pushToken = [[[[deviceToken description]
                                stringByReplacingOccurrencesOfString:@"<"withString:@""] stringByReplacingOccurrencesOfString:@">"
                                                                                 
                    withString:@""] stringByReplacingOccurrencesOfString:@"
"withString:@""] ;
                2、编码为GB2312的NSData转换为NSString:
                     NSStringEncoding encoding = CFStringConvertEncodingToNSStringEncoding(kCFStringEncodingGB_18030_2000);

                     NSString *text = [[NSString alloc] initWithData:data encoding:encoding];  

                    
                     [ _responseText appendString:text];

2，NSData 与 Byte

　　NSData --> Byte

　　NSString *testString = @"1234567890";

　　NSData *testData = [testString dataUsingEncoding: NSUTF8StringEncoding];

　　Byte *testByte = (Byte *)[testData bytes];

　　Byte --> NSData

　　Byte byte[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23};
　　NSData *adata = [[NSData alloc] initWithBytes:byte length:24];

3，NSData 与 UIImage

　　NSData --> UIImage
　　UIImage *aimage = [UIImage imageWithData: imageData];

　　//例：从本地文件沙盒中取图片并转换为NSData

　　NSString *path = [[NSBundle mainBundle] bundlePath];

　　NSString *name = [NSString stringWithFormat:@"ceshi.png"];

　　NSString *finalPath = [path stringByAppendingPathComponent:name];

　　NSData *imageData = [NSData dataWithContentsOfFile: finalPath];

　　UIImage *aimage = [UIImage imageWithData: imageData];

　　UIImage－> NSData

　　NSData *imageData = UIImagePNGRepresentation(aimae);

4，NSData 与 NSMutableData

　　NSData --> MSMutableData

　　NSData *data=[[NSData alloc]init];

　　NSMutableData *mdata=[[NSMutableData alloc]init];   

　　mdata=[NSData dataWithData:data];

5，NSData合并为一个NSMutableData

1 - (NSString *)filePathWithName:(NSString *)filename
2 {
3         NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
4         NSString *documentsDirectory = [paths objectAtIndex:0];
5         return [documentsDirectory stringByAppendingPathComponent:filename];
6 }
7
8 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
9     //音频文件路径
10         NSString *mp3Path1 = [[NSBundle mainBundle] pathForResource:@"1" ofType:@"mp3"];
11         NSString *mp3Path2 = [[NSBundle mainBundle] pathForResource:@"2" ofType:@"mp3"];
12         //音频数据
13         NSData *sound1Data = [[NSData alloc] initWithContentsOfFile: mp3Path1];
14         NSData *sound2Data = [[NSData alloc] initWithContentsOfFile: mp3Path2];
15         //合并音频
16         NSMutableData *sounds = [NSMutableData alloc];
17         [sounds appendData:sound1Data];
18         [sounds appendData:sound2Data];
19         //保存音频
20
21         NSLog(@"data length:%d", [sounds length]);
22
23         [sounds writeToFile:[self filePathWithName:@"tmp.mp3"] atomically:YES];
24
25         [window makeKeyAndVisible];
26
27     return YES;
28 }

 6，NSString 合并

1 NSString* string; // 结果字符串
2 NSString* string1, string2; //已存在的字符串，需要将string1和string2连接起来
3 //方法1.
4 string = [NSString initWithFormat:@"%@,%@", string1, string2 ];
5 //方法2.
6 string = [string1 stringByAppendingString:string2];
7 //方法3 .
8 string = [string stringByAppendingFormat:@"%@,%@",string1, string2];