1.首先推出选择拍照还是相册的alert，代码如下：
UIAlertController *alert = [UIAlertController alertControllerWithTitle:nil message:nil preferredStyle: UIAlertControllerStyleActionSheet];
UIAlertAction *photo = [UIAlertAction actionWithTitle:@"拍照" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
[self readImageFromCamera];
}];
UIAlertAction *albulm = [UIAlertAction actionWithTitle:@"相册" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
[self readImageFromAlbum];
}];
UIAlertAction *cancel = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {
[self dismissViewControllerAnimated:YES completion:nil];
}];
[alert addAction:photo];
[alert addAction:albulm];
[alert addAction:cancel];
[self presentViewController:alert animated:YES completion:nil];
2.创建UIImagePickerController,设置imagepicker的sourcetype为camera还是library,设置代理，设置imagepicker的alllowsediting为yes；
3.在imagepicker的代理方法(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary*)info中，取出想要的照片，为info[UIImagePickerControllerEditedImage];info的key海域IImagePickerControllerOriginalImage；
4.对图片进行相应size的压缩
image = [self scaleImage:image toSize:CGSizeMake(750, 750)];
- (UIImage *)scaleImage:(UIImage *)image toSize:(CGSize)size {
if (image.size.width > size.width) {
UIGraphicsBeginImageContext(size);
[image drawInRect:CGRectMake(0, 0, size.width, size.height)];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
} else {
return image;
}
}
