如何获取手机系统相册中的图片

• 单张

1> UIImagePickerController
 2> AssetsLibrary框架
 3> Photos框架

• 多张

 1> AssetsLibrary框架
 2> Photos框架

• 示例代码

#import "ViewController.h"
#import <Photos/Photos.h>
#import <CTAssetsPickerController/CTAssetsPickerController.h>
@interface ViewController ()<CTAssetsPickerControllerDelegate >

@end

@implementation ViewController



-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    [PHPhotoLibrary requestAuthorization:^(PHAuthorizationStatus status) {
        
        //如果用户不允许访问相册,就直接返回
        if (status != PHAuthorizationStatusAuthorized) return;
        
        dispatch_async(dispatch_get_main_queue(), ^{
        
            //创建第三方框架提供的控制器
            CTAssetsPickerController *picker = [[CTAssetsPickerController alloc] init];
            
            //设置代理
            picker.delegate = self;
            
            //设置相册的类型 : 相机胶卷 + 自定义相册
            picker.assetCollectionSubtypes = @[
                                               @(PHAssetCollectionSubtypeSmartAlbumUserLibrary),
                                           @(PHAssetCollectionSubtypeAlbumRegular)
                                               
                                               ];
            //并且不要显示空的相册
            picker.showsEmptyAlbums = NO;
            
            //设置所选照片的索引
            picker.showsSelectionIndex = YES;
            
            [self presentViewController:picker animated:YES completion:nil];
        });
        
    }];
}

#pragma mark - CTAssetsPickerControllerDelegate

//当用户选择照片完成后调用(将图片显示在控制器的View上面)
-(void)assetsPickerController:(CTAssetsPickerController *)picker didFinishPickingAssets:(NSArray *)assets
{
    //关闭图片选择界面
    [picker dismissViewControllerAnimated:YES completion:nil];
    
    //可以获取所有选中的图片
//    NSLog(@"%@",assets);
    
    //获取屏幕像素与点坐标的比值
    CGFloat scale = [UIScreen mainScreen].scale;
    
    PHImageRequestOptions *options = [[PHImageRequestOptions alloc] init];
    options.resizeMode = PHImageRequestOptionsResizeModeExact;
    options.deliveryMode = PHImageRequestOptionsDeliveryModeHighQualityFormat;
    
    //遍历选择的所有图片
    for (NSInteger i = 0; i < assets.count; i++) {
       
        PHAsset *asset = assets[i];
        
        //计算图片的尺寸
        CGSize size = CGSizeMake(asset.pixelWidth / scale, asset.pixelHeight / scale);
        
        //获取图片
        [[PHImageManager defaultManager] requestImageForAsset:asset targetSize:size contentMode:PHImageContentModeDefault options:options resultHandler:^(UIImage * _Nullable result, NSDictionary * _Nullable info) {
            
            //获取图片成功就会来到这个block中
            UIImageView *imageView = [[UIImageView alloc] init];
            imageView.image = result;
            imageView.frame = CGRectMake((i % 3)*92.5, (i / 3)*92.5, 92.5, 92.5);
            [self.view addSubview:imageView];
        }];
    }
   
}

//控制器是否允许用户去选择照片
-(BOOL)assetsPickerController:(CTAssetsPickerController *)picker shouldSelectAsset:(PHAsset *)asset
{
    NSInteger max = 2;
    
    if (picker.selectedAssets.count >= max) {
        
        //提示用户最多只能选择的张数
        NSString *massage = [NSString stringWithFormat:@"最多只能选%zd张",max];
        
        UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"提示" message:massage preferredStyle:UIAlertControllerStyleAlert];
        
        UIAlertAction *action1 = [UIAlertAction actionWithTitle:@"好的" style:UIAlertActionStyleDefault handler:nil];
        
        [alert addAction:action1];
        
        //这里不能使用self来modal别的控制器,因为此时self.view不在window上,如果A想modal出B,那么A必须要在窗口上
        //用self会报警告
        /*
         Warning: Attempt to present <UIAlertController: 0x7fb8f1f3bab0> on <ViewController: 0x7fb8f1c207a0> whose view is not in the window hierarchy!

         */
        [picker presentViewController:alert animated:YES completion:nil];
        
        return NO;
    }
    return YES;
}

@end