swift - 如何在运行时修改view.alphaValue并生效

Question

我在运行时修改了 alphaValue 但没有任何效果，请问是什么问题。如何在运行时修改 alphaValue ？

我想在运行时调整 View 的alphaValue

Xcode 10.2.1 Swift 4.2

//
//  ViewController.swift
//  macosappalphaValuetest
//
//  Created by miller on 2019/7/25.
//  Copyright © 2019 miller. All rights reserved.
//

import Cocoa

class ViewController: NSViewController {

    @IBAction func btnclick1(_ sender: Any) {
       self.view.alphaValue = 0.8

    }


    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

    override var representedObject: Any? {
        didSet {
        // Update the view, if already loaded.
        }
    }

    override func viewWillAppear() {
        super.viewWillAppear()
        view.window?.isOpaque = false
        view.window?.backgroundColor = NSColor(red: 0.5, green: 0.5, blue: 0.5, alpha: 0.5)
        self.view.alphaValue = 0.4
        }

    }

Answer 1

在NSViewController的viewWillAppear方法中，你的 View 窗口可能是nil。您可以通过打印print(view.window)来检查它。因此，您需要获取窗口的正确实例。参见下面的方法:

func validWindow() -> NSWindow? {
    var window = NSApplication.shared.mainWindow
    if (window == nil) {
        window = NSApplication.shared.windows.first
    }
    return window
}

只需编写以下代码即可使窗口透明:

guard let window = self.validWindow() else { return }
window.alphaValue = 0.5

这对我来说效果很好。

输出:

递归地增加和减少 alpha 值:

func decreaseAlpha(_ window: NSWindow) {
    let alpha = window.alphaValue - 0.1
    if alpha < 0.0 {
        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.1) {
            self.increaseAlpha(window)
        }
        return
    }

    window.alphaValue = alpha
    DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.1) {
        self.decreaseAlpha(window)
    }
}

func increaseAlpha(_ window: NSWindow) {
    let alpha = window.alphaValue + 0.1
    if alpha > 1.0 {
        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.1) {
            self.decreaseAlpha(window)
        }
        return
    }

    window.alphaValue = alpha
    DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.1) {
        self.increaseAlpha(window)
    }
}

并在viewDidLoad:方法中写入:

guard let window = self.validWindow() else { return }
decreaseAlpha(window)

输出: