我想知道我的iPhone应用如何将特定的UIView作为UIImage截屏。
我尝试了这段代码，但我得到的只是一个空白图片。
UIGraphicsBeginImageContext(CGSizeMake(320,480));
CGContextRef context = UIGraphicsGetCurrentContext();
[myUIView.layer drawInContext:context];
UIImage *screenShot = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
myUIView的尺寸为320x480，并且它有一些子视图。
正确的做法是什么？
iOS 7推出了一种全新的方法，可以将视图层次结构绘制到当前的图形上下文中。这可以用于快速获取UIImage。
我在UIView上实现了一个分类方法，以获取视图作为UIImage：
- (UIImage *)pb_takeSnapshot {
UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO, [UIScreen mainScreen].scale);
[self drawViewHierarchyInRect:self.bounds afterScreenUpdates:YES];
// old style [self.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
这个方法比现有的renderInContext:方法要快得多。
参考：https://developer.apple.com/library/content/qa/qa1817/_index.html
Swift更新：一个做同样事情的扩展：
extension UIView {
func pb_takeSnapshot() -> UIImage {
UIGraphicsBeginImageContextWithOptions(bounds.size, false, UIScreen.mainScreen().scale)
drawViewHierarchyInRect(self.bounds, afterScreenUpdates: true)
// old style: layer.renderInContext(UIGraphicsGetCurrentContext())
let image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return image
}
}
更新 Swift 3 版本
UIGraphicsBeginImageContextWithOptions(bounds.size, false, UIScreen.main.scale)
drawHierarchy(in: self.bounds, afterScreenUpdates: true)
let image = UIGraphicsGetImageFromCurrentImageContext()!
UIGraphicsEndImageContext()
return image
0代替UIScreen.main.scale。 - Frederik Winkelsdorf我认为你可能需要使用renderInContext而不是drawInContext。 drawInContext更多是你会重写的方法...
请注意，它可能无法在所有视图中工作，特别是大约一年前当我试图在实时相机视图中使用它时，它并未起作用。
为了截取屏幕截图或一个UIView，你需要捕获关键窗口。你可以使用UIGraphicsBeginImageContextWithOptions并将其比例参数设置为0.0f以在Retina分辨率下进行捕获。它总是以本地分辨率（iPhone 4及更高版本的Retina）进行捕获。
这个代码可以进行全屏截图（关键窗口）。
UIWindow *keyWindow = [[UIApplication sharedApplication] keyWindow];
CGRect rect = [keyWindow bounds];
UIGraphicsBeginImageContextWithOptions(rect.size,YES,0.0f);
CGContextRef context = UIGraphicsGetCurrentContext();
[keyWindow.layer renderInContext:context];
UIImage *capturedScreen = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
这段代码可以以本机分辨率捕捉一个 UIView。
CGRect rect = [captureView bounds];
UIGraphicsBeginImageContextWithOptions(rect.size,YES,0.0f);
CGContextRef context = UIGraphicsGetCurrentContext();
[captureView.layer renderInContext:context];
UIImage *capturedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
如果需要，这将以95％的质量将UIImage保存在应用程序的文档文件夹中，格式为jpg。
NSString *imagePath = [NSHomeDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"Documents/capturedImage.jpg"]];
[UIImageJPEGRepresentation(capturedImage, 0.95) writeToFile:imagePath atomically:YES];
iOS7及以上版本，我们有以下默认方法：
- (UIView *)snapshotViewAfterScreenUpdates:(BOOL)afterUpdates
drawViewHierarchyInRect:afterScreenUpdates: 方法。
https://developer.apple.com/library/ios/documentation/uikit/reference/uiview_class/uiview/uiview.htmliOS 10有一个新的API。
extension UIView {
func makeScreenshot() -> UIImage {
let renderer = UIGraphicsImageRenderer(bounds: self.bounds)
return renderer.image { (context) in
self.layer.render(in: context.cgContext)
}
}
}
我已经在Swift中创建了可用的UIView扩展来进行屏幕截图:
extension UIView{
var screenshot: UIImage{
UIGraphicsBeginImageContext(self.bounds.size);
let context = UIGraphicsGetCurrentContext();
self.layer.renderInContext(context)
let screenShot = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return screenShot
}
}
使用它只需键入：
let screenshot = view.screenshot
UIGraphicsBeginImageContextWithOptions(self.bounds.size, false, 0);而不是UIGraphicsBeginImageContext(self.bounds.size);以使用设备的正确比例因子。 - knshndrawViewHierarchyInRect而不是renderInContext则不行。 - Mike Demidov- (void)drawRect:(CGRect)rect {
UIGraphicsBeginImageContext(self.bounds.size);
[self.view.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIImageWriteToSavedPhotosAlbum(viewImage, nil, nil, nil);
}
这种方法可以放在您的控制器类中。
drawRect 不是 UIViewController 的一部分（如果我没记错的话）。它是 UIView 的一部分。我认为如果它在控制器中，它不会被调用。 - jwwimport UIKit
extension CALayer {
func makeSnapshot() -> UIImage? {
let scale = UIScreen.main.scale
UIGraphicsBeginImageContextWithOptions(frame.size, false, scale)
defer { UIGraphicsEndImageContext() }
guard let context = UIGraphicsGetCurrentContext() else { return nil }
render(in: context)
let screenshot = UIGraphicsGetImageFromCurrentImageContext()
return screenshot
}
}
extension UIView {
func makeSnapshot() -> UIImage? {
if #available(iOS 10.0, *) {
let renderer = UIGraphicsImageRenderer(size: frame.size)
return renderer.image { _ in drawHierarchy(in: bounds, afterScreenUpdates: true) }
} else {
return layer.makeSnapshot()
}
}
}
let image = view.makeSnapshot()
不要忘记在这里添加解决方案代码
import UIKit
class ViewController: UIViewController {
@IBOutlet var viewForScreenShot: UIView!
@IBOutlet var screenShotRenderer: UIImageView!
@IBAction func makeViewScreenShotButtonTapped2(_ sender: UIButton) {
screenShotRenderer.image = viewForScreenShot.makeSnapshot()
}
}
Main.storyboard
<?xml version="1.0" encoding="UTF-8"?>
<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="11762" systemVersion="16C67" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" colorMatched="YES" initialViewController="BYZ-38-t0r">
<device id="retina4_7" orientation="portrait">
<adaptation id="fullscreen"/>
</device>
<dependencies>
<deployment identifier="iOS"/>
<plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="11757"/>
<capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
</dependencies>
<scenes>
<!--View Controller-->
<scene sceneID="tne-QT-ifu">
<objects>
<viewController id="BYZ-38-t0r" customClass="ViewController" customModule="stackoverflow_2214957" customModuleProvider="target" sceneMemberID="viewController">
<layoutGuides>
<viewControllerLayoutGuide type="top" id="y3c-jy-aDJ"/>
<viewControllerLayoutGuide type="bottom" id="wfy-db-euE"/>
</layoutGuides>
<view key="view" contentMode="scaleToFill" id="8bC-Xf-vdC">
<rect key="frame" x="0.0" y="0.0" width="375" height="667"/>
<autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
<subviews>
<view contentMode="scaleToFill" translatesAutoresizingMaskIntoConstraints="NO" id="Acg-GO-mMN">
<rect key="frame" x="67" y="28" width="240" height="128"/>
<subviews>
<textField opaque="NO" clipsSubviews="YES" contentMode="scaleToFill" contentHorizontalAlignment="left" contentVerticalAlignment="center" borderStyle="roundedRect" textAlignment="natural" minimumFontSize="17" translatesAutoresizingMaskIntoConstraints="NO" id="4Fr-O3-56t">
<rect key="frame" x="72" y="49" width="96" height="30"/>
<constraints>
<constraint firstAttribute="height" constant="30" id="cLv-es-h7Q"/>
<constraint firstAttribute="width" constant="96" id="ytF-FH-gdm"/>
</constraints>
<nil key="textColor"/>
<fontDescription key="fontDescription" type="system" pointSize="14"/>
<textInputTraits key="textInputTraits"/>
</textField>
</subviews>
<color key="backgroundColor" red="0.0" green="0.47843137250000001" blue="1" alpha="0.49277611300000002" colorSpace="custom" customColorSpace="sRGB"/>
<color key="tintColor" white="0.66666666666666663" alpha="1" colorSpace="calibratedWhite"/>
<constraints>
<constraint firstItem="4Fr-O3-56t" firstAttribute="centerX" secondItem="Acg-GO-mMN" secondAttribute="centerX" id="egj-rT-Gz5"/>
<constraint firstItem="4Fr-O3-56t" firstAttribute="centerY" secondItem="Acg-GO-mMN" secondAttribute="centerY" id="ymi-Ll-WIV"/>
</constraints>
</view>
<button opaque="NO" contentMode="scaleToFill" contentHorizontalAlignment="center" contentVerticalAlignment="center" buttonType="roundedRect" lineBreakMode="middleTruncation" translatesAutoresizingMaskIntoConstraints="NO" id="SQq-IE-pvj">
<rect key="frame" x="109" y="214" width="157" height="30"/>
<state key="normal" title="make view screen shot"/>
<connections>
<action selector="makeViewScreenShotButtonTapped2:" destination="BYZ-38-t0r" eventType="touchUpInside" id="KSY-ec-uvA"/>
</connections>
</button>
<imageView userInteractionEnabled="NO" contentMode="scaleAspectFit" horizontalHuggingPriority="251" verticalHuggingPriority="251" translatesAutoresizingMaskIntoConstraints="NO" id="CEZ-Ju-Tpq">
<rect key="frame" x="67" y="269" width="240" height="128"/>
<constraints>
<constraint firstAttribute="width" constant="240" id="STo-iJ-rM4"/>
<constraint firstAttribute="height" constant="128" id="tfi-zF-zdn"/>
</constraints>
</imageView>
</subviews>
<color key="backgroundColor" red="0.95941069162436543" green="0.95941069162436543" blue="0.95941069162436543" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
<constraints>
<constraint firstItem="CEZ-Ju-Tpq" firstAttribute="top" secondItem="SQq-IE-pvj" secondAttribute="bottom" constant="25" id="6x1-iB-gKF"/>
<constraint firstItem="Acg-GO-mMN" firstAttribute="leading" secondItem="CEZ-Ju-Tpq" secondAttribute="leading" id="LUp-Be-FiC"/>
<constraint firstItem="SQq-IE-pvj" firstAttribute="top" secondItem="Acg-GO-mMN" secondAttribute="bottom" constant="58" id="Qu0-YT-k9O"/>
<constraint firstItem="Acg-GO-mMN" firstAttribute="centerX" secondItem="8bC-Xf-vdC" secondAttribute="centerX" id="Qze-zd-ajY"/>
<constraint firstItem="Acg-GO-mMN" firstAttribute="trailing" secondItem="CEZ-Ju-Tpq" secondAttribute="trailing" id="b1d-sp-GHD"/>
<constraint firstItem="SQq-IE-pvj" firstAttribute="centerX" secondItem="CEZ-Ju-Tpq" secondAttribute="centerX" id="qCL-AF-Cro"/>
<constraint firstItem="Acg-GO-mMN" firstAttribute="top" secondItem="y3c-jy-aDJ" secondAttribute="bottom" constant="8" symbolic="YES" id="u5Y-eh-oSG"/>
<constraint firstItem="CEZ-Ju-Tpq" firstAttribute="centerY" secondItem="8bC-Xf-vdC" secondAttribute="centerY" id="vkx-JQ-pOF"/>
</constraints>
</view>
<connections>
<outlet property="screenShotRenderer" destination="CEZ-Ju-Tpq" id="8QB-OE-ib6"/>
<outlet property="viewForScreenShot" destination="Acg-GO-mMN" id="jgL-yn-8kk"/>
</connections>
</viewController>
<placeholder placeholderIdentifier="IBFirstResponder" id="dkx-z0-nzr" sceneMemberID="firstResponder"/>
</objects>
<point key="canvasLocation" x="32.799999999999997" y="37.331334332833585"/>
</scene>
</scenes>
</document>
CGImageRef UIGetScreenImage();
现在，即使是私有 API，苹果也允许我们在公共应用程序中使用它。
苹果不允许使用以下代码：
CGImageRef UIGetScreenImage();
应用程序应该使用 drawRect 方法按照以下规定进行截屏：
http://developer.apple.com/library/ios/#qa/qa2010/qa1703.html