Question

我正在尝试在UIActionSheet中单击按钮后显示UIImagePickerController。代码很简单。但是，[[UIImagePickerController alloc] init]的呼叫在完成之前会挂起几秒。我没有在模拟器中看到这种行为，但我在iPod和iPhone上看到它。

以下是UIActionSheetDelegate方法。添加了日志消息以显示执行时间。

- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {
    NSLog(@"Action sheet clicked button at index %d", buttonIndex);
    switch (buttonIndex) {
        case kSelectFromCameraButtonIndex:
            [self showImagePickerWithCamera];
            break;
        case kSelectFromPhotoLibraryButtonIndex:
            [self showImagePickerWithPhotoLibrary];
            break;
    }
}

- (void)actionSheet:(UIActionSheet *)actionSheet willDismissWithButtonIndex:(NSInteger)buttonIndex {
    NSLog(@"Action sheet will dismiss with button index %d", buttonIndex);
}

- (void)actionSheet:(UIActionSheet *)actionSheet didDismissWithButtonIndex:(NSInteger)buttonIndex {
    NSLog(@"Action sheet did dismiss with button index %d", buttonIndex);
}

这是实际创建UIImagePickerController的代码：

- (void)showImagePickerWithPhotoLibrary {
    NSLog(@"Showing image picker with photo library");
    if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypePhotoLibrary]) {

        NSLog(@"Creating picker");
        UIImagePickerController *picker = [[UIImagePickerController alloc] init];

        NSLog(@"Setting picker settings");
        picker.delegate = self;
        picker.allowsEditing = YES;
        picker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;

        NSLog(@"Presenting picker as modal view controller");
        [self presentModalViewController:picker animated:YES];

        NSLog(@"Releasing picker");
        [picker release];
    }
}

没有什么花哨的事情发生。但是，如果查看控制台输出，您会注意到创建UIImagePickerController的行需要 7秒才能完成。

2010-09-21 15:23:26.107 Oh Snap[1264:307] Action sheet clicked button at index 1
2010-09-21 15:23:26.113 Oh Snap[1264:307] Showing image picker with photo library
2010-09-21 15:23:26.120 Oh Snap[1264:307] Creating picker
2010-09-21 15:23:33.111 Oh Snap[1264:307] Setting picker settings
2010-09-21 15:23:33.123 Oh Snap[1264:307] Presenting picker as modal view controller
2010-09-21 15:23:33.136 Oh Snap[1264:307] Using two-stage rotation animation. To use the smoother single-stage animation, this application must remove two-stage method implementations.
2010-09-21 15:23:33.144 Oh Snap[1264:307] Using two-stage rotation animation is not supported when rotating more than one view controller or view controllers not the window delegate
2010-09-21 15:23:33.289 Oh Snap[1264:307] Releasing picker
2010-09-21 15:23:33.299 Oh Snap[1264:307] Action sheet will dismiss with button index 1
2010-09-21 15:23:33.916 Oh Snap[1264:307] Action sheet did dismiss with button index 1

任何人都知道造成这种情况的原因是什么？

Answer 1

我在我的应用程序中注意到UIImagePickerController需要很长时间才能创建。解决方法是在需要之前实例化它，即使在单独的线程上，然后在需要时再显示它。我假设但不能确定这是苹果公司如何让它快速合理起来的。

Answer 2

请注意，这种延迟似乎只发生在iPhone 4上：在同一代的iPod Touch上，它几乎没有问题。

我使用NSOperation在后台实例化图像选择器实例。 show / hide spinner方法在图像视图中添加/删除UIActivityIndicatorView我正在显示相机图片。

  NSOperationQueue *operations = ...

  ...

  [self showSpinner];

  [operations addOperation: 
    [NSBlockOperation blockOperationWithBlock: 
     ^{
        UIImagePickerController *cameraUI = [UIImagePickerController new];

        cameraUI.sourceType = UIImagePickerControllerSourceTypeCamera;
        cameraUI.allowsEditing = NO;
        cameraUI.delegate = self;

        [self performSelectorOnMainThread: @selector (showImagePicker:) 
                               withObject: cameraUI waitUntilDone: YES];
     }]];

  ...


 - (void) showImagePicker: (UIImagePickerController *) picker
 {
   [self hideSpinner];
   [self presentModalViewController: picker animated: YES];
 }

UIImagePickerController创建挂起几秒钟

2 个答案: