iOS数据类型转换 NSData转NSString,Byte,UIImage

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1,NSData 与 NSString
  NSData --> NSString
  NSString *aString = [[NSString alloc] initWithData:adata encoding:NSUTF8StringEncoding];
  NSString --> NSData
  NSString *aString = @"1234";
  NSData *aData = [aString dataUsingEncoding: NSUTF8StringEncoding];
   iOS NSString 和NSData 转换
   NSString 转换成NSData 对象 
   NSData* xmlData = [@"testdata" dataUsingEncoding:NSUTF8StringEncoding]; 
   NSData 转换成NSString对象 
   NSData * data; 
   NSString *result = [[NSString alloc] initWithData:data  encoding:NSUTF8StringEncoding];
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
- (NSString *)filePathWithName:(NSString *)filename
 {
         NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
         NSString *documentsDirectory = [paths objectAtIndex:0];
         return [documentsDirectory stringByAppendingPathComponent:filename];
 }
 
 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    
     //音频文件路径
         NSString *mp3Path1 = [[NSBundle mainBundle] pathForResource:@"1" ofType:@"mp3"];
         NSString *mp3Path2 = [[NSBundle mainBundle] pathForResource:@"2" ofType:@"mp3"];
         //音频数据
         NSData *sound1Data = [[NSData alloc] initWithContentsOfFile: mp3Path1];
         NSData *sound2Data = [[NSData alloc] initWithContentsOfFile: mp3Path2];
         //合并音频
         NSMutableData *sounds = [NSMutableData alloc];
         [sounds appendData:sound1Data];
         [sounds appendData:sound2Data];
         //保存音频
 
         NSLog(@"data length:%d", [sounds length]);
 
         [sounds writeToFile:[self filePathWithName:@"tmp.mp3"] atomically:YES];
         
         [window makeKeyAndVisible];
     
     return YES;
 }