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76 lines
3.1 KiB
76 lines
3.1 KiB
//
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// Placeholder.swift
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// Kingfisher
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//
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// Created by Tieme van Veen on 28/08/2017.
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//
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// Copyright (c) 2019 Wei Wang <onevcat@gmail.com>
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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// THE SOFTWARE.
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#if os(macOS)
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import AppKit
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#else
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import UIKit
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#endif
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/// Represents a placeholder type which could be set while loading as well as
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/// loading finished without getting an image.
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public protocol Placeholder {
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/// How the placeholder should be added to a given image view.
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func add(to imageView: ImageView)
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/// How the placeholder should be removed from a given image view.
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func remove(from imageView: ImageView)
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}
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/// Default implementation of an image placeholder. The image will be set or
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/// reset directly for `image` property of the image view.
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extension Image: Placeholder {
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/// How the placeholder should be added to a given image view.
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public func add(to imageView: ImageView) { imageView.image = self }
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/// How the placeholder should be removed from a given image view.
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public func remove(from imageView: ImageView) { imageView.image = nil }
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}
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/// Default implementation of an arbitrary view as placeholder. The view will be
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/// added as a subview when adding and be removed from its super view when removing.
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///
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/// To use your customize View type as placeholder, simply let it conforming to
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/// `Placeholder` by `extension MyView: Placeholder {}`.
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extension Placeholder where Self: View {
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/// How the placeholder should be added to a given image view.
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public func add(to imageView: ImageView) {
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imageView.addSubview(self)
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translatesAutoresizingMaskIntoConstraints = false
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centerXAnchor.constraint(equalTo: imageView.centerXAnchor).isActive = true
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centerYAnchor.constraint(equalTo: imageView.centerYAnchor).isActive = true
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heightAnchor.constraint(equalTo: imageView.heightAnchor).isActive = true
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widthAnchor.constraint(equalTo: imageView.widthAnchor).isActive = true
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}
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/// How the placeholder should be removed from a given image view.
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public func remove(from imageView: ImageView) {
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removeFromSuperview()
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}
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}
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