在 Cocoa，Objective C 中绘制选择框（橡皮筋，行军蚂蚁）

Question

我目前使用鼠标事件实现了一个简单的选择框，并在鼠标拖动时重绘了一个矩形。这是我的代码：

-(void)drawRect:(NSRect)dirtyRect
{
if (!NSEqualRects(self.draggingBox, NSZeroRect))
{
    [[NSColor grayColor] setStroke];
    [[NSBezierPath bezierPathWithRect:self.draggingBox] stroke];
}
}

#pragma mark Mouse Events

- (void)mouseDown:(NSEvent *)theEvent
{
    NSPoint pointInView = [self convertPoint:[theEvent locationInWindow] fromView:nil];
    self.draggingBox = NSMakeRect(pointInView.x, pointInView.y, 0, 0);
    [self setNeedsDisplay:YES];
}

- (void)mouseDragged:(NSEvent *)theEvent
{
    NSPoint pointInView = [self convertPoint:[theEvent locationInWindow] fromView:nil];
    _draggingBox.size.width = pointInView.x - (self.draggingBox.origin.x);
    _draggingBox.size.height = pointInView.y - (self.draggingBox.origin.y);
    [self setNeedsDisplay:YES];
}

- (void)mouseUp:(NSEvent *)theEvent
{
    self.draggingBox = NSZeroRect;
    [self setNeedsDisplay:YES];
}

参考：http://cocoadev.com/HowToCreateWalkingAnts

问题：

这是最有效的方法吗？如果视图很复杂，在主视图上绘制透明视图而不是在鼠标拖动期间不断重绘视图会更有效吗（http://www.cocoabuilder.com/archive/cocoa/99877-drawing-selection-rectangle.html）？这是怎么做到的？我似乎找不到任何例子。

Answer 1

如果您愿意，您可以使用 QuartzCore 为您制作“行军蚂蚁”的动画。这也使您完全摆脱了手动绘制橡皮筋选择框的世界。您只需定义定义该框的路径，并让 Core Animation 负责绘制该框并为其设置动画。

在 XIB 的“View Effects”Inspector 中，打开“Core Animation”，然后你可以这样做：

#import <QuartzCore/QuartzCore.h>
#import "CustomView.h"

@interface CustomView ()

@property (nonatomic) NSPoint startPoint;
@property (nonatomic, strong) CAShapeLayer *shapeLayer;

@end

@implementation CustomView

#pragma mark Mouse Events

- (void)mouseDown:(NSEvent *)theEvent
{
    self.startPoint = [self convertPoint:[theEvent locationInWindow] fromView:nil];

    // create and configure shape layer

    self.shapeLayer = [CAShapeLayer layer];
    self.shapeLayer.lineWidth = 1.0;
    self.shapeLayer.strokeColor = [[NSColor blackColor] CGColor];
    self.shapeLayer.fillColor = [[NSColor clearColor] CGColor];
    self.shapeLayer.lineDashPattern = @[@10, @5];
    [self.layer addSublayer:self.shapeLayer];

    // create animation for the layer

    CABasicAnimation *dashAnimation;
    dashAnimation = [CABasicAnimation animationWithKeyPath:@"lineDashPhase"];
    [dashAnimation setFromValue:@0.0f];
    [dashAnimation setToValue:@15.0f];
    [dashAnimation setDuration:0.75f];
    [dashAnimation setRepeatCount:HUGE_VALF];
    [self.shapeLayer addAnimation:dashAnimation forKey:@"linePhase"];
}

- (void)mouseDragged:(NSEvent *)theEvent
{
    NSPoint point = [self convertPoint:[theEvent locationInWindow] fromView:nil];

    // create path for the shape layer

    CGMutablePathRef path = CGPathCreateMutable();
    CGPathMoveToPoint(path, NULL, self.startPoint.x, self.startPoint.y);
    CGPathAddLineToPoint(path, NULL, self.startPoint.x, point.y);
    CGPathAddLineToPoint(path, NULL, point.x, point.y);
    CGPathAddLineToPoint(path, NULL, point.x, self.startPoint.y);
    CGPathCloseSubpath(path);

    // set the shape layer's path

    self.shapeLayer.path = path;

    CGPathRelease(path);
}

- (void)mouseUp:(NSEvent *)theEvent
{
    [self.shapeLayer removeFromSuperlayer];
    self.shapeLayer = nil;
}

@end

这样，Core Animation 会为你照顾行军的蚂蚁。

Answer 2

swift 3 版本：

import Cocoa
import QuartzCore

class myView: NSView {

    //MARK:Properties
    var startPoint : NSPoint!
    var shapeLayer : CAShapeLayer!

    override func draw(_ dirtyRect: NSRect) {
        super.draw(dirtyRect)

        // Drawing code here.
    }


    override func mouseDown(with event: NSEvent) {

        self.startPoint = self.convert(event.locationInWindow, from: nil)

        shapeLayer = CAShapeLayer()
        shapeLayer.lineWidth = 1.0
        shapeLayer.fillColor = NSColor.clear.cgColor
        shapeLayer.strokeColor = NSColor.black.cgColor
        shapeLayer.lineDashPattern = [10,5]
        self.layer?.addSublayer(shapeLayer)

        var dashAnimation = CABasicAnimation()
        dashAnimation = CABasicAnimation(keyPath: "lineDashPhase")
        dashAnimation.duration = 0.75
        dashAnimation.fromValue = 0.0
        dashAnimation.toValue = 15.0
        dashAnimation.repeatCount = .infinity
        shapeLayer.add(dashAnimation, forKey: "linePhase")




    }

    override func mouseDragged(with event: NSEvent) {

        let point : NSPoint = self.convert(event.locationInWindow, from: nil)
        let path = CGMutablePath()
        path.move(to: self.startPoint)
        path.addLine(to: NSPoint(x: self.startPoint.x, y: point.y))
        path.addLine(to: point)
        path.addLine(to: NSPoint(x:point.x,y:self.startPoint.y))
        path.closeSubpath()
        self.shapeLayer.path = path
    }

    override func mouseUp(with event: NSEvent) {
        self.shapeLayer.removeFromSuperlayer()
        self.shapeLayer = nil
    }


}

Answer 3

这篇文章有点老了，但我在网上仍然没有找到好的解决方案（框架）。但我想这是每个人总有一天都必须掌握的任务（内容选择），而且苹果没有为此提供 API。不过我自己做了框架，放到 Github 上：https://github.com/ckteebe/MultiSelectionSuiteFramework.

Answer 4

如果有人需要 Swift 2.0 版本，这里是：

import Cocoa
import QuartzCore


class myView: NSView {

var startPoint : NSPoint!
var shapeLayer : CAShapeLayer!



override func drawRect(dirtyRect: NSRect) {
    super.drawRect(dirtyRect)

    // Drawing code here.
}


override func mouseDown(theEvent: NSEvent) {

    self.startPoint = self.convertPoint(theEvent.locationInWindow, fromView: nil)

    shapeLayer = CAShapeLayer()
    shapeLayer.lineWidth = 1.0
    shapeLayer.fillColor = NSColor.clearColor().CGColor
    shapeLayer.strokeColor = NSColor.blackColor().CGColor
    shapeLayer.lineDashPattern = [10,5]
    self.layer?.addSublayer(shapeLayer)

    var dashAnimation = CABasicAnimation()
    dashAnimation = CABasicAnimation(keyPath: "lineDashPhase")
    dashAnimation.duration = 0.75
    dashAnimation.fromValue = 0.0
    dashAnimation.toValue = 15.0
    dashAnimation.repeatCount = .infinity
    shapeLayer.addAnimation(dashAnimation, forKey: "linePhase")




}

override func mouseDragged(theEvent: NSEvent) {

    let point : NSPoint = self.convertPoint(theEvent.locationInWindow, fromView: nil)
    let path = CGPathCreateMutable()
    CGPathMoveToPoint(path, nil, self.startPoint.x, self.startPoint.y)
    CGPathAddLineToPoint(path, nil, self.startPoint.x, point.y)
    CGPathAddLineToPoint(path, nil, point.x, point.y)
    CGPathAddLineToPoint(path, nil, point.x, self.startPoint.y)
    CGPathCloseSubpath(path)
    self.shapeLayer.path = path
}

override func mouseUp(theEvent: NSEvent) {
    self.shapeLayer.removeFromSuperlayer()
    self.shapeLayer = nil
}



}