確定UIScrollview中縮放和平移圖像的中心

Question

我正在為iPhone開發一個照片應用程序，該應用程序允許用戶使用相機拍攝照片或從“相機膠卷”中抓取一張照片，然后根據需要在UIScrollView中平移和縮放該圖像。 然后，用戶點擊按鈕以保存圖像。 我在使用key方法時遇到麻煩，該方法返回嵌入在scrollview中的imageview的可見區域的確切中心。 我需要這種方法來允許設備屏幕尺寸的變化（例如，iPhone 4 vs 5），以及源圖像的大小，縱橫比和縮放比例的變化。

舉例來說，我需要使它適用於以下情況：

• iPhone 5屏幕尺寸為320 X 568
• Scrollview框架尺寸為320 X 568
• 寬度為380，高​​度為284的圖像
• 縮放比例為3.0

另外，我也需要它來工作：

• 屏幕尺寸為320 X 480的iPhone 4
• Scrollview框架尺寸為320 X 480
• 尺寸為640寬度和1048高度的圖像
• 縮放比例為1.3

以下是我當前的代碼，該代碼試圖考慮屏幕尺寸和圖像尺寸的變化，但不適用於iPhone 4和5以及所有類型的圖像，例如縱向或橫向格式。 有沒有更簡單的方法來獲取滾動視圖的可見部分的中心點？ 我需要對如何解釋和操作視圖的屬性（例如bounds.origin和bounds.size）以及如何在滾動視圖中使用內容大小和縮放比例有更清楚的了解。

我看過各種相似的問題，但似乎沒有一個問題足以說明設備或圖像縱橫比或大小的所有變化。 任何幫助將不勝感激！

類似問題

如何確定滾動視圖中當前可見的區域並確定中心？

在UIScrollView內獲取UIImage可見部分的正確坐標

- (CGPoint)centerOfVisibleFrame:(UIImage *)image inScrollView:(UIScrollView *)scrollView
{
    CGPoint frameCenter;

    CGFloat zoomScale = scrollView.zoomScale;

    // First determine the dimensions of the device
    CGSize deviceFrameSize = [UIScreen mainScreen].bounds.size;

    // Need to determine the scale factor for adjusting the image to full width/full height
    CGFloat imageDeviceAspectFitScale;

    // Compare the aspect ratio (height / width) of the device to the aspect ratio of the image
    CGFloat deviceAspectRatio = deviceFrameSize.height / deviceFrameSize.width;
    CGFloat imageAspectRatio = image.size.height / image.size.width;

    // If the device's aspect ratio is greater than the image aspect ratio
    if (deviceAspectRatio > imageAspectRatio)
    {
        // Set the imageDeviceAspectFitScale for full width
        imageDeviceAspectFitScale = image.size.width / deviceFrameSize.width;
    }
    // Otherwise the image's aspect ratio is greater than the device aspect ratio
    else
    {
        // Set the imageDeviceAspectFitScale for full height
        imageDeviceAspectFitScale = image.size.height / deviceFrameSize.height;
    }

    // Create the frame for the image at full width or full height
    CGSize imageAspectFitSize;
    imageAspectFitSize.width = image.size.width / imageDeviceAspectFitScale;
    imageAspectFitSize.height = image.size.height / imageDeviceAspectFitScale;

    // Calculate the vertical and horizontal offset to adjust the coordinates of the
    // image center to account for greater device height or device width
    CGFloat verticalOffset = deviceFrameSize.height - imageAspectFitSize.height;
    CGFloat horizontalOffset = deviceFrameSize.width - imageAspectFitSize.width;

    if (self.debug) NSLog(@"verticalOffset = %f horizontalOffset = %f", verticalOffset, horizontalOffset);

    if (self.debug) NSLog(@"image.size.width: %f image.size.height: %f", image.size.width, image.size.height);

    if (self.debug) NSLog(@"scrollView.frame.size w: %f h: %f", scrollView.frame.size.width, scrollView.frame.size.height);

    if (self.debug) NSLog(@"scrollView.bounds.size.width: %f scrollView.bounds.size.height: %f",
                          scrollView.bounds.size.width, scrollView.bounds.size.height);

    if (self.debug) NSLog(@"scrollView.contentSize w=%f h=%f", scrollView.contentSize.width, scrollView.contentSize.height);

    // imageRect represents the coordinate space for the image, adjusted for zoom scale
    CGRect imageRect;

    // First use the visible frame's origin to determine the top left corner of the visible rectangle
    imageRect.origin.x = scrollView.contentOffset.x;
    imageRect.origin.y = scrollView.contentOffset.y;

    if (self.debug) NSLog(@"imageRect.origin x = %f y = %f", imageRect.origin.x, imageRect.origin.y);

    // Adjust the image rect for zoom - Multiply by zoom scale
    imageRect.size.width = image.size.width * zoomScale;
    imageRect.size.height = image.size.height * zoomScale;

    if (self.debug) NSLog(@"Zoomed imageRect.size width = %f height = %f", imageRect.size.width, imageRect.size.height);

    // Then scale the image down to fit into the device frame
    // Divide by the image device aspect fit scale
    imageRect.size.width = imageRect.size.width / imageDeviceAspectFitScale;
    imageRect.size.height = imageRect.size.height / imageDeviceAspectFitScale;

    if (self.debug) NSLog(@"CVF Aspect fit imageRect.size width = %f height = %f", imageRect.size.width, imageRect.size.height);

    // Then calculate the frame center by using the x and y dimensions of the DEVICE frame
    frameCenter.x = imageRect.origin.x + (deviceFrameSize.width / 2);
    frameCenter.y = imageRect.origin.y + (deviceFrameSize.height / 2);

    // Scale back to original image dimensions from zoom
    frameCenter.x = frameCenter.x / zoomScale;
    frameCenter.y = frameCenter.y / zoomScale;

    if (self.debug) NSLog(@"frameCenter.x = %f frameCenter.y = %f", frameCenter.x, frameCenter.y);

    // Scale back up for the aspect fit scale
    frameCenter.x = frameCenter.x * imageDeviceAspectFitScale;
    frameCenter.y = frameCenter.y * imageDeviceAspectFitScale;

    // Correct the coordinates for horizontal and vertical offset
    frameCenter.x = frameCenter.x - (horizontalOffset);
    frameCenter.y = frameCenter.y - (verticalOffset);

    if (self.debug) NSLog(@"CVF frameCenter.x = %f frameCenter.y = %f", frameCenter.x, frameCenter.y);

    return frameCenter;


}

Answer 1

基本上，這使您可以看到滾動視圖的矩形。

CGRect visibleRect = [yourScrollView convertRect:yourScrollView.bounds toView:yourImageview];

要么

CGRect visibleRect;
visibleRect.origin = scrollView.contentOffset;
visibleRect.size = scrollView.frame.size;

請查看此問題和答案以獲取更多詳細信息。 獲取UIScrollView的content的可見區域 。

只要您知道矩形，就可以輕松計算出中心點。