在启动UIImagePickerController之前显示UIAlertView

Question

我的应用程序通过UIActionSheet向用户询问他们想要从（Photo Library或Camera）导入图像，然后启动相应的UIImagePickerController。

如果用户选择相机，我想首先显示带有与应用相关的相机说明图像的UIAlertView。这样可行，但是当警报仍在屏幕上并显示在屏幕后面时，UIImagePickerController会启动。如果用户取消UIAlert，我该如何启动相机？

-(void) actionSheet:(UIActionSheet *)actionSheet didDismissWithButtonIndex:(NSInteger)buttonIndex {
if (buttonIndex != [actionSheet cancelButtonIndex]) {
    // User hasn't canceled, launch chosen photo source
    NSString *selectedButtonTitle = [actionSheet buttonTitleAtIndex:buttonIndex];
    if ([selectedButtonTitle isEqualToString:@"Camera"]) {

        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@"\n\n\n\n\n\n\n\n\n\n" delegate:self cancelButtonTitle:@"Done" otherButtonTitles:nil];
        UIImageView *cameraHelpView = [[UIImageView alloc] initWithFrame:CGRectMake(82, 46, 120, 160)];
        UIImage *cameraTutorial = [UIImage imageNamed:@"cameraTutorial.png"];
        cameraHelpView.image = cameraTutorial;
        [alert addSubview:cameraHelpView];
        [alert show];
        [alert release];

        UIImagePickerController *picker = [[UIImagePickerController alloc] init];
        picker.delegate = self;
        picker.sourceType = UIImagePickerControllerSourceTypeCamera;    
        [self presentModalViewController: picker animated: YES];
        [picker release];
    }

Answer 1

为UIAlertView实现委托并实现alertView：didDismissWithButtonIndex：以启动UIImagePickerController。