iOS练习-使用Camera来获取图片

Time: 23 March 2015
Categories:
iOS 30
Tags:
Objective-c 30

利用Camera或者直接访问相册来获取图片是很方便的，iOS提供了UIImagePickerController类来管理用户和Camera或图片库的交互。接下来就通过一个简单的demo来体验这个类的使用方法。

###准备工作

创建一个单页app，加入一个UIImageView，两个button，并合理的排版。两个button的title分别为：takePhoto和selectPhoto。选中UIImageView，在右侧面板中取消AutoLayout，因为我们想保持现有的布局。将刚加入的三个UI控件和ViewController建立连接。

@interface APPViewController : UIViewController
@property (strong, nonatomic) IBOutlet UIImageView *imageView;
- (IBAction)takePhoto:  (UIButton *)sender;
- (IBAction)selectPhoto:(UIButton *)sender;
@end

###调整ViewController

要实现和camera或图片库的交互，我们要通过delegate来实现，所以我们要遵循UIImagePickerControllerDelegate协议，另外我们使用模态形式展示camera或图片库，故我们还需要遵循UINavigationControllerDelegate协议。所以头文件的部分内容如下：

@interface APPViewController : UIViewController <UIImagePickerControllerDelegate, UINavigationControllerDelegate>

为了实现拍照功能，我们要创建一个UIImagePickerController,并将它委托给AppViewController处理。可以通过指定image picker的sourceType属性来决定图片来源。当image picker创建后，我们可以通过它的presentViewController来展示它。

- (IBAction)takePhoto:(UIButton *)sender {
    UIImagePickerController *picker = [[UIImagePickerController alloc] init];
    picker.delegate = self;
    picker.allowsEditing = YES;
    picker.sourceType = UIImagePickerControllerSourceTypeCamera;
    [self presentViewController:picker animated:YES completion:NULL];
}
//from photo library
- (IBAction)selectPhoto:(UIButton *)sender {
    UIImagePickerController *picker = [[UIImagePickerController alloc] init];
    picker.delegate = self;
    picker.allowsEditing = YES;
    picker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
    [self presentViewController:picker animated:YES completion:NULL];
}

###实现图片捕获的委托

当用户拍照或者进行图片调整后，会触发didFinishPickingMediaWithInfo ，第一个参数是方法的调用者（picker），当我们有多个imagePicker时特别有用。第二个参数包含了图片的相关信息。

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
    UIImage *chosenImage = info[UIImagePickerControllerEditedImage];
    self.imageView.image = chosenImage;
    [picker dismissViewControllerAnimated:YES completion:NULL];
}

当用户取消拍照时会触发imagePickerControllerDidCancel ，我们也要来实现这个方法：

- (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker {
    [picker dismissViewControllerAnimated:YES completion:NULL];
}

准备工作都差不多好了，现在，当我们buildAndRun的时候，发现报错了。这是因为模拟器中没有Camera，所以会报错。所以，我们将一个错误处理信息来保证体验的完整性。

if (![UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {
        UIAlertView *myAlertView = [[UIAlertView alloc] initWithTitle:@"Error" message:@"Device has no camera" delegate:nil  cancelButtonTitle:@"OK" otherButtonTitles: nil];
        [myAlertView show];
}