Getting a screenshot of a UIScrollView, including

问题:

I have a UIScrollView decendent that implements a takeScreenshot method that looks like this:

-(void)takeScreenshot {  
  CGRect contextRect  = CGRectMake(0, 0, 768, 1004);
  UIGraphicsBeginImageContext(contextRect.size);    
  [self.layer renderInContext:UIGraphicsGetCurrentContext()];
  UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();

  // do something with the viewImage here.
}

This basically moves to the top of the scroll view, and takes a screenshot of the visible area. It works fine when the iPad is oriented portrait, but when it\'s in landscape the bottom of the image is cut off (as the height of the visible area is only 748, not 1004).

Is it possible to get a snapshot of the UIScrollView, including areas not on screen? Or do I need to scroll the view down, take a second photo and stitch them together?

回答1:

Here is code that works ...

- (IBAction) renderScrollViewToImage
{
    UIImage* image = nil;

    UIGraphicsBeginImageContext(_scrollView.contentSize);
    {
        CGPoint savedContentOffset = _scrollView.contentOffset;
        CGRect savedFrame = _scrollView.frame;

        _scrollView.contentOffset = CGPointZero;
        _scrollView.frame = CGRectMake(0, 0, _scrollView.contentSize.width, _scrollView.contentSize.height);

        [_scrollView.layer renderInContext: UIGraphicsGetCurrentContext()];     
        image = UIGraphicsGetImageFromCurrentImageContext();

        _scrollView.contentOffset = savedContentOffset;
        _scrollView.frame = savedFrame;
    }
    UIGraphicsEndImageContext();

    if (image != nil) {
        [UIImagePNGRepresentation(image) writeToFile: @\"/tmp/test.png\" atomically: YES];
        system(\"open /tmp/test.png\");
    }
}

The last few lines simply write the image to /tmp/test.png and then opens it in Preview.app. This obviously only works on in the Simulator :-)

Complete project in the ScrollViewScreenShot Github Repository

回答2:

for me answer https://stackoverflow.com/a/3539944/4164443 didn\'t work. I had a task of implementing this on iOS 8.

Actually this method works for iPhone, but iPad (both simu and real device) is another case. It just renders visible part and the rest of image is just blank.

I tried with drawViewHierarchyInRect - no luck. Depending on afterScreenUpdates being true or false I got stretched part of image or again only part of image.

So the only way I found to achieve correct screenshoting is to add scrollview to another temp view and render it.

Sample code is below (scrollview is outlet in my VC)

func getImageOfScrollView()->UIImage{
    var image = UIImage();

    UIGraphicsBeginImageContextWithOptions(self.scrollView.contentSize, false, UIScreen.mainScreen().scale)

    // save initial values
    let savedContentOffset = self.scrollView.contentOffset;
    let savedFrame = self.scrollView.frame;
    let savedBackgroundColor = self.scrollView.backgroundColor

    // reset offset to top left point
    self.scrollView.contentOffset = CGPointZero;
    // set frame to content size
    self.scrollView.frame = CGRectMake(0, 0, self.scrollView.contentSize.width, self.scrollView.contentSize.height);
    // remove background
    self.scrollView.backgroundColor = UIColor.clearColor()

    // make temp view with scroll view content size
    // a workaround for issue when image on ipad was drawn incorrectly
    let tempView = UIView(frame: CGRectMake(0, 0, self.scrollView.contentSize.width, self.scrollView.contentSize.height))

    // save superview
    let tempSuperView = self.scrollView.superview
    // remove scrollView from old superview
    self.scrollView.removeFromSuperview()
    // and add to tempView
    tempView.addSubview(self.scrollView)

    // render view
    // drawViewHierarchyInRect not working correctly
    tempView.layer.renderInContext(UIGraphicsGetCurrentContext())
    // and get image
    image = UIGraphicsGetImageFromCurrentImageContext();

    // and return everything back
    tempView.subviews[0].removeFromSuperview()
    tempSuperView?.addSubview(self.scrollView)

    // restore saved settings
    self.scrollView.contentOffset = savedContentOffset;
    self.scrollView.frame = savedFrame;
    self.scrollView.backgroundColor = savedBackgroundColor

    UIGraphicsEndImageContext();

    return image
}

回答3:

Working Example of UIView Extension with handling for UIScrollView:

extension UIView {
    func screenshot() -> UIImage {

            if(self is UIScrollView) {
                let scrollView = self as! UIScrollView

                let savedContentOffset = scrollView.contentOffset
                let savedFrame = scrollView.frame

                UIGraphicsBeginImageContext(scrollView.contentSize)
                scrollView.contentOffset = .zero
                self.frame = CGRect(x: 0, y: 0, width: scrollView.contentSize.width, height: scrollView.contentSize.height)
                self.layer.render(in: UIGraphicsGetCurrentContext()!)
                let image = UIGraphicsGetImageFromCurrentImageContext()
                UIGraphicsEndImageContext();

                scrollView.contentOffset = savedContentOffset
                scrollView.frame = savedFrame

                return image!
            }

            UIGraphicsBeginImageContext(self.bounds.size)
            self.layer.render(in: UIGraphicsGetCurrentContext()!)
            let image = UIGraphicsGetImageFromCurrentImageContext()
            UIGraphicsEndImageContext()
            return image!

        }
}

回答4:

I took the solution above from @Roopesh Mittal and made it safer/cleaner.

Swift 4 compatible

fileprivate extension UIScrollView {
    func screenshot() -> UIImage? {
        let savedContentOffset = contentOffset
        let savedFrame = frame

        UIGraphicsBeginImageContext(contentSize)
        contentOffset = .zero
        frame = CGRect(x: 0, y: 0, width: contentSize.width, height: contentSize.height)

        guard let context = UIGraphicsGetCurrentContext() else { return nil }

        layer.render(in: context)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext();

        contentOffset = savedContentOffset
        frame = savedFrame

        return image
    }
}

回答5:

If you don\'t want to expand your scroll view beyond the entire screen (and it won\'t work with autolayout anyway) there\'s a better way.

You can use core graphics transforms in conjunction with the contentOffset of the scroll view to accomplish the same thing.

//
//  ScrollViewSnapshotter.swift
//  ScrollViewSnapshotter
//
//  Created by Moshe Berman on 4/10/16.
//  Copyright © 2016 Moshe Berman. All rights reserved.
//

import UIKit

class ScrollViewSnapshotter: NSObject {


func PDFWithScrollView(scrollview: UIScrollView) -> NSData {

    /**
     *  Step 1: The first thing we need is the default origin and size of our pages.
     *          Since bounds always start at (0, 0) and the scroll view\'s bounds give us
     *          the correct size for the visible area, we can just use that.
     *
     *          In the United States, a standard printed page is 8.5 inches by 11 inches,
     *          but when generating a PDF it\'s simpler to keep the page size matching the
     *          visible area of the scroll view. We can let our printer software (such
     *          as the Preview app on OS X or the Printer app on iOS) do the scaling.
     *
     *          If we wanted to scale ourselves, we could multiply each of those
     *          numbers by 72, to get the number of points for each dimension.
     *          We would have to change how we generated the the pages below, so
     *          for simplicity, we\'re going to stick to one page per screenful of content.
     */

    let pageDimensions = scrollview.bounds

    /**
     *  Step 2: Now we need to know how many pages we will need to fit our content.
     *          To get this, we divide our scroll views dimensions by the size
     *          of each page, in either direction.
     *          We also need to round up, so that the pages don\'t get clipped.
     */

    let pageSize = pageDimensions.size
    let totalSize = scrollview.contentSize

    let numberOfPagesThatFitHorizontally = Int(ceil(totalSize.width / pageSize.width))
    let numberOfPagesThatFitVertically = Int(ceil(totalSize.height / pageSize.height))

    /**
     *  Step 3: Set up a Core Graphics PDF context.
     *
     *          First we create a backing store for the PDF data, then
     *          pass it and the page dimensions to Core Graphics.
     *
     *          We could pass in some document information here, which mostly cover PDF metadata,
     *          including author name, creator name (our software) and a password to
     *          require when viewing the PDF file.
     *
     *          Also note that we can use UIGraphicsBeginPDFContextToFile() instead,
     *          which writes the PDF to a specified path. I haven\'t played with it, so
     *          I don\'t know if the data is written all at once, or as each page is closed.
     */

    let outputData = NSMutableData()

    UIGraphicsBeginPDFContextToData(outputData, pageDimensions, nil)

    /**
     *  Step 4: Remember some state for later.
     *          Then we need to clear the content insets, so that our
     *          core graphics layer and our content offset match up.
     *          We don\'t need to reset the content offset, because that
     *          happens implicitly, in the loop below.
     */

    let savedContentOffset = scrollview.contentOffset
    let savedContentInset = scrollview.contentInset

    scrollview.contentInset = UIEdgeInsetsZero

    /**
     *  Step 6: Now we loop through the pages and generate the data for each page.
     */

    if let context = UIGraphicsGetCurrentContext()
    {
        for indexHorizontal in 0 ..< numberOfPagesThatFitHorizontally
        {
            for indexVertical in 0 ..< numberOfPagesThatFitVertically
            {

                /**
                 *  Step 6a: Start a new page.
                 *
                 *          This automatically closes the previous page.
                 *          There\'s a similar method UIGraphicsBeginPDFPageWithInfo,
                 *          which allows you to configure the rectangle of the page and
                 *          other metadata.
                 */

                UIGraphicsBeginPDFPage()

                /**
                 *  Step 6b:The trick here is to move the visible portion of the
                 *          scroll view *and* adjust the core graphics context
                 *          appropriately.
                 *
                 *          Consider that the viewport of the core graphics context
                 *          is attached to the top of the scroll view\'s content view
                 *          and we need to push it in the opposite direction as we scroll.
                 *          Further, anything not inside of the visible area of the scroll
                 *          view is clipped, so scrolling will move the core graphics viewport
                 *          out of the rendered area, producing empty pages.
                 *
                 *          To counter this, we scroll the next screenful into view, and adjust
                 *          the core graphics context. Note that core graphics uses a coordinate
                 *          system which has the y coordinate decreasing as we go from top to bottom.
                 *          This is the opposite of UIKit (although it matches AppKit on OS X.)
                 */

                let offsetHorizontal = CGFloat(indexHorizontal) * pageSize.width
                let offsetVertical = CGFloat(indexVertical) * pageSize.height

                scrollview.contentOffset = CGPointMake(offsetHorizontal, offsetVertical)
                CGContextTranslateCTM(context, -offsetHorizontal, -offsetVertical) // NOTE: Negative offsets

                /**
                 *  Step 6c: Now we are ready to render the page.
                 *
                 *  There are faster ways to snapshot a view, but this
                 *  is the most straightforward way to render a layer
                 *  into a context.
                 */

                scrollview.layer.renderInContext(context)
            }
        }
    }

    /**
     *  Step 7: End the document context.
     */

    UIGraphicsEndPDFContext()

    /**
     *  Step 8: Restore the scroll view.
     */

    scrollview.contentInset = savedContentInset
    scrollview.contentOffset = savedContentOffset

    /**
     *  Step 9: Return the data.
     *          You can write it to a file, or display it the user,
     *          or even pass it to iOS for sharing.
     */

    return outputData
}
}

Here\'s a blog post I wrote explaining the process.

The process for generating a PDF is very similar to snapshotting an image, except instead of pages, you\'d need to make one large canvas that matches the size of the scroll view and then grab the contents in chunks.

回答6:

SWIFT 3 version:

func snapshot() -> UIImage?
{      
    UIGraphicsBeginImageContext(scrollView.contentSize)

    let savedContentOffset = scrollView.contentOffset
    let savedFrame = scrollView.frame

    scrollView.contentOffset = CGPoint.zero
    scrollView.frame = CGRect(x: 0, y: 0, width: scrollView.contentSize.width, height: scrollView.contentSize.height)

    scrollView.layer.render(in: UIGraphicsGetCurrentContext()!)
    let image = UIGraphicsGetImageFromCurrentImageContext()

    scrollView.contentOffset = savedContentOffset
    scrollView.frame = savedFrame

    UIGraphicsEndImageContext()

    return image
}

This worked for me

回答7:

A refined Swift 4.1 version, based on @RyanG \'s answer:

fileprivate extension UIScrollView {
    func screenshot() -> UIImage? {
        // begin image context
        UIGraphicsBeginImageContextWithOptions(contentSize, false, 0.0)
        // save the orginal offset & frame 
        let savedContentOffset = contentOffset
        let savedFrame = frame
        // end ctx, restore offset & frame before returning
        defer {
            UIGraphicsEndImageContext()
            contentOffset = savedContentOffset
            frame = savedFrame
        }
        // change the offset & frame so as to include all content
        contentOffset = .zero
        frame = CGRect(x: 0, y: 0, width: contentSize.width, height: contentSize.height)
        guard let ctx = UIGraphicsGetCurrentContext() else {
            return nil
        }
        layer.render(in: ctx)
        let image = UIGraphicsGetImageFromCurrentImageContext()

        return image
    }
}

回答8:

Here\'s another way of doing it, which takes the zoom level into account. I have a scrollview with 4 different UIImageView layers in it, and I want to take a screenshot of their current state:

float theScale = 1.0f / theScrollView.zoomScale;
// The viewing rectangle in absolute coordinates
CGRect visibleArea = CGRectMake((int)(theScrollView.contentOffset.x * theScale), (int)(theScrollView.contentOffset.y * theScale),
                                (int)(theScrollView.bounds.size.width * theScale), (int)(theScrollView.bounds.size.height * theScale));

NSArray *layers = [NSArray arrayWithObjects:imageLayer1, imageLayer2, imageLayer3, imageLayer4, nil];
UIGraphicsBeginImageContext(visibleArea.size);
for (UIImageView *layer in layers) {
    CALayer *coreLayer = layer.layer;
    coreLayer.bounds = CGRectMake(layer.frame.origin.x - visibleArea.origin.x, layer.frame.origin.y - visibleArea.origin.y, layer.frame.size.width, layer.frame.size.height);
    [coreLayer renderInContext:UIGraphicsGetCurrentContext()];
}
UIImage *screenshot = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

This takes the screenshot in absolute coordinates. That is, if you have a 2048*2048 image in the scrollview and you can see about a quarter of it, then regardless of the resolution of your screen it would take a screenshot of 512*512. If you want to take a screenshot at your screen resolution (say, 320*480) then you have to adjust the image as follows, directly after the above code:

UIGraphicsBeginImageContext(theScrollView.frame.size);
[screenshot drawInRect:CGRectMake(0, 0, theScrollView.frame.size.width, theScrollView.frame.size.height)];
UIImage *smallScreenshot = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

回答9:

SWIFT 3 version thanks to @gleb vodovozov:

func getImageOfScrollView()->UIImage{
    var image = UIImage();

    UIGraphicsBeginImageContextWithOptions(self.scrollView.contentSize, false, UIScreen.main.scale)

    // save initial values
    let savedContentOffset = self.scrollView.contentOffset;
    let savedFrame = self.scrollView.frame;
    let savedBackgroundColor = self.scrollView.backgroundColor

    // reset offset to top left point
    self.scrollView.contentOffset = CGPoint.zero;
    // set frame to content size
    self.scrollView.frame = CGRect(x: 0, y: 0, width: self.scrollView.contentSize.width, height: self.scrollView.contentSize.height)
    // remove background
    self.scrollView.backgroundColor = UIColor.clear

    // make temp view with scroll view content size
    // a workaround for issue when image on ipad was drawn incorrectly
    let tempView = UIView(frame: CGRect(x: 0, y: 0, width: self.scrollView.contentSize.width, height: self.scrollView.contentSize.height))

    // save superview
    let tempSuperView = self.scrollView.superview
    // remove scrollView from old superview
    self.scrollView.removeFromSuperview()
    // and add to tempView
    tempView.addSubview(self.scrollView)

    // render view
    // drawViewHierarchyInRect not working correctly
    tempView.layer.render(in: UIGraphicsGetCurrentContext()!)
    // and get image
    image = UIGraphicsGetImageFromCurrentImageContext()!;

    // and return everything back
    tempView.subviews[0].removeFromSuperview()
    tempSuperView?.addSubview(self.scrollView)

    // restore saved settings
    self.scrollView.contentOffset = savedContentOffset;
    self.scrollView.frame = savedFrame;
    self.scrollView.backgroundColor = savedBackgroundColor

    UIGraphicsEndImageContext();

    return image
}

回答10:

I don\'t know much but I can guess that if we set the size of the contextRect like this for landscape, it may work well:

  CGRect contextRect  = CGRectMake(0, 0, 1004, 768*2);

Because this contextRect will determine the size of the UIGraphicsBeginImageContext so I hope that double the height can solve your problem