ObjectC 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];

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;
}

 6，NSString 合并

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