Bluetooth implements peer-to-peer networking <GameKit/GameKit.h>

/*
 1. Set up the UI interface
 2. Introduce the framework
 3. Click to select photo
 4. Connect the Bluetooth device
 5. Implement the proxy method of Bluetooth
 6. Send photos
 */

#import "ViewController.h"
#import <GameKit/GameKit.h>

@interface ViewController ()<UINavigationControllerDelegate, UIImagePickerControllerDelegate, GKPeerPickerControllerDelegate>

@property (nonatomic, strong) UIImageView *imgView;
@property (nonatomic, strong) UIButton *selectImgBtn;
@property (nonatomic, strong) UIButton *connectionDeviceBtn;
@property (nonatomic, strong) UIButton *sendImgBtn;
@property (nonatomic, strong) GKSession *seccion;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    _imgView = [[UIImageView alloc] initWithFrame:CGRectMake(10, 20, self.view.bounds.size.width - 20, self.view.bounds.size.width - 20)];
    _imgView.backgroundColor = [UIColor lightGrayColor];
    [self.view addSubview:_imgView];
    
    _selectImgBtn = [UIButton buttonWithType:UIButtonTypeSystem];
    _selectImgBtn.frame = CGRectMake(10, CGRectGetMaxY(_imgView.frame) + 30, 60, 30);
    [_selectImgBtn setTitle: @" Select Photo " forState:UIControlStateNormal];
    [self.view addSubview:_selectImgBtn];
    [_selectImgBtn addTarget:self action:@selector(clickSelectImgBtnAction) forControlEvents:UIControlEventTouchUpInside];
    
    _connectionDeviceBtn = [UIButton buttonWithType:UIButtonTypeSystem];
    _connectionDeviceBtn.frame = CGRectMake(0, 0, 60, 30);
    CGPoint p = CGPointMake(self.view.center.x, _selectImgBtn.center.y);
    _connectionDeviceBtn.center = p;
    [_connectionDeviceBtn setTitle: @" connection device " forState:UIControlStateNormal];
    [self.view addSubview:_connectionDeviceBtn];
    [_connectionDeviceBtn addTarget:self action:@selector(clickConnectionDeviceBtnAction) forControlEvents:UIControlEventTouchUpInside];
    
    _sendImgBtn = [UIButton buttonWithType:UIButtonTypeSystem];
    _sendImgBtn.frame = CGRectMake(self.view.bounds.size.width - 70, CGRectGetMinY(_selectImgBtn.frame), 60, 30);
    [_sendImgBtn setTitle: @" Send photo " forState:UIControlStateNormal];
    [self.view addSubview:_sendImgBtn];
    [_sendImgBtn addTarget:self action:@selector(clickSendImgBtnAction) forControlEvents:UIControlEventTouchUpInside];
}

// Select image 
- ( void )clickSelectImgBtnAction {
    
    // 0. Determine if the photo is available 
    if (! [UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypePhotoLibrary]) {
        
        return;
    }
    // 1. Create controller 
    UIImagePickerController *ipc = [UIImagePickerController new ];
     // 2. Set image source 
    ipc.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
     // 3. Set delegate 
    ipc. delegate = self;
     // 4. Display controller 
    [self presentViewController:ipc animated:YES completion:nil];
    
}

// Connect Device 
- ( void )clickConnectionDeviceBtnAction {
    
    // 1. Create controller 
    GKPeerPickerController *pic = [GKPeerPickerController new ];
     // 2. Connect device to get data 
    pic. delegate = self;
     // 3. Display controller 
    [pic show];
}

// Send image 
- ( void ) clickSendImgBtnAction {
    
    // 0. A data object is needed to convert the image into data data
     // CGFloat compressionQuality precision, compression ratio 
    NSData *data = UIImageJPEGRepresentation(self.imgView.image, 0.2 );
     // 1. Send data through session 
    /*
     datagrams (packets, small chunks)
     GKSendDataReliable, when the network data is sent incorrectly, it can ensure that the messages arrive in the order sent
     GKSendDataUnreliable is only sent once
     */
    [self.seccion sendDataToAllPeers:data withDataMode:GKSendDataReliable error:nil];
}

Proxy for #pragma Albums
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info {
    
    NSLog(@"--info-- = %@", info);
    UIImage *image = info[UIImagePickerControllerOriginalImage];
    _imgView.image = image;
    [picker dismissViewControllerAnimated:YES completion:nil];
}

#pragma mark - GKPeerPickerControllerDelegate
- (void)peerPickerController:(GKPeerPickerController *)picker didConnectPeer:(NSString *)peerID toSession:(GKSession *)session {
    
    self.seccion = session;
     // 1. Set the session session, Handler (handle, similar to proxy) 
    [session setDataReceiveHandler:self withContext:nil];
     // 2. Remove the controller 
    [picker dismiss];
}

// 从setDataReceiveHandler里面找出来
- (void)receiveData:(NSData *)data formPeer:(NSString *)peer inSession:(GKSession *)session context:(void *)context {
    
    UIImage *image = [UIImage imageWithData:data];
    _imgView.image = image;
}