iOS平台Eyedropper工具：能否单独调用UIColorPickerViewController取色器？

首先明确：iOS系统没有提供直接单独调用UIColorPickerViewController内置取色器（Eyedropper）的API，必须通过完整的UIColorPickerViewController模态弹窗来触发这个工具，这是系统层面的功能限制。

给你几个适合新手的可行方案：

方案1：简化系统ColorPicker的展示 #

虽然不能单独调用取色器，但可以调整UIColorPickerViewController的展示样式，让它更聚焦于取色功能：

• 缩小弹窗尺寸，减少无关区域的干扰
• 关闭透明度调节等不需要的功能

示例代码：

import UIKit

class ViewController: UIViewController, UIColorPickerViewControllerDelegate {
    @IBAction func openEyedropperButtonTapped(_ sender: UIButton) {
        let colorPicker = UIColorPickerViewController()
        colorPicker.delegate = self
        // 设置默认选中颜色
        colorPicker.selectedColor = .systemOrange
        // 关闭透明度调节
        colorPicker.supportsAlpha = false
        // 缩小弹窗尺寸
        colorPicker.preferredContentSize = CGSize(width: 320, height: 450)
        
        present(colorPicker, animated: true)
    }
    
    // 获取选中的颜色
    func colorPickerViewControllerDidSelectColor(_ viewController: UIColorPickerViewController) {
        let pickedColor = viewController.selectedColor
        // 这里处理选中的颜色，比如更新按钮背景色
        if let button = viewController.presentingViewController?.view.viewWithTag(100) as? UIButton {
            button.backgroundColor = pickedColor
        }
        dismiss(animated: true)
    }
}

用户打开弹窗后，只需要点击顶部的取色器图标即可使用取色功能，对新手来说成本较低。

方案2：自行实现简易取色器 #

如果希望完全跳过系统ColorPicker，可以用屏幕截图+点击取色的方式实现一个基础取色器，适合App内的取色场景：

示例代码：

import UIKit

extension ViewController {
    @IBAction func showCustomEyedropper(_ sender: UIButton) {
        guard let window = view.window else { return }
        
        // 生成当前界面的截图
        let renderer = UIGraphicsImageRenderer(bounds: window.bounds)
        let screenshot = renderer.image { context in
            window.drawHierarchy(in: window.bounds, afterScreenUpdates: true)
        }
        
        // 创建全屏半透明视图展示截图
        let eyedropperOverlay = UIImageView(image: screenshot)
        eyedropperOverlay.frame = window.bounds
        eyedropperOverlay.backgroundColor = UIColor.black.withAlphaComponent(0.2)
        eyedropperOverlay.isUserInteractionEnabled = true
        
        // 添加点击手势识别器
        let tapGesture = UITapGestureRecognizer(target: self, action: #selector(handleEyedropperTap(_:)))
        eyedropperOverlay.addGestureRecognizer(tapGesture)
        
        window.addSubview(eyedropperOverlay)
    }
    
    @objc private func handleEyedropperTap(_ gesture: UITapGestureRecognizer) {
        guard let overlay = gesture.view as? UIImageView, let image = overlay.image else {
            overlay.removeFromSuperview()
            return
        }
        
        let tapPoint = gesture.location(in: overlay)
        let scale = image.scale
        let pixelPosition = CGPoint(x: tapPoint.x * scale, y: tapPoint.y * scale)
        
        // 提取点击位置的颜色
        guard let cgImage = image.cgImage else {
            overlay.removeFromSuperview()
            return
        }
        
        let width = cgImage.width
        let bytesPerRow = 4 * width
        let pixelBuffer = UnsafeMutablePointer<UInt8>.allocate(capacity: bytesPerRow * cgImage.height)
        
        let colorSpace = CGColorSpaceCreateDeviceRGB()
        let context = CGContext(data: pixelBuffer,
                                width: width,
                                height: cgImage.height,
                                bitsPerComponent: 8,
                                bytesPerRow: bytesPerRow,
                                space: colorSpace,
                                bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)
        
        context?.draw(cgImage, in: CGRect(x: 0, y: 0, width: width, height: cgImage.height))
        
        let pixelIndex = Int((pixelPosition.y * CGFloat(width)) + pixelPosition.x) * 4
        let red = CGFloat(pixelBuffer[pixelIndex]) / 255.0
        let green = CGFloat(pixelBuffer[pixelIndex + 1]) / 255.0
        let blue = CGFloat(pixelBuffer[pixelIndex + 2]) / 255.0
        let alpha = CGFloat(pixelBuffer[pixelIndex + 3]) / 255.0
        
        let pickedColor = UIColor(red: red, green: green, blue: blue, alpha: alpha)
        
        // 处理取到的颜色，比如更新按钮样式
        if let button = view.viewWithTag(200) as? UIButton {
            button.backgroundColor = pickedColor
        }
        
        // 清理资源
        overlay.removeFromSuperview()
        pixelBuffer.deallocate()
    }
}

这个方案的优势是完全自定义，不需要依赖系统弹窗；缺点是只能取当前App界面内的颜色，无法跨App取色（跨App取色需要特殊权限，新手暂时不用考虑）。

补充说明 #

如果你的需求是跨App取色，那只能依赖系统的UIColorPickerViewController，因为第三方App无法直接获取其他App的界面内容，这是iOS的隐私安全限制。

内容的提问来源于stack exchange，提问作者CodeyTown