objective-c - 移动 NSView 直到它碰到边界

Question

在基于 Cocoa 的应用程序中，我有一个用于绘图的 Canvas ，它继承自 NSView，还有一个矩形，也继承自 NSView。在 Canvas 内部拖动矩形是没有问题的:

-(void)mouseDragged:(NSEvent *)theEvent {
  NSPoint myOrigin = self.frame.origin;

  [self setFrameOrigin:NSMakePoint(myOrigin.x + [theEvent deltaX], 
                                   myOrigin.y - [theEvent deltaY])];
}

像魅力一样工作。我现在遇到的问题:如何防止矩形移出 Canvas ？

所以，首先我想只为左边框修复这个问题，然后调整其他边缘。我的第一个想法是:“检查矩形的 x 原点是否为负数”。但是:一旦它为负，矩形就不能再四处移动(自然地)。我通过将矩形移动到 else 分支中的零 x 偏移来解决这个问题。这行得通，但是……很丑。

所以我对这个有点困惑，有什么提示吗？解决方案绝对是近在咫尺且简单易行。太简单了，我想不出来(一如既往的简单解决方案；)。

问候

苹果电脑

Answer 1

我建议不要使用 deltaX 和 deltaY；尝试在 superview 中使用事件的位置。您将需要对 subview 的引用。

// In the superview
- (void)mouseDragged:(NSEvent *)event {
    NSPoint mousePoint = [self convertPoint:[event locationInWindow] 
                             fromView:nil];

    // Could also add the width of the moving rectangle to this check 
    // to keep any part of it from going outside the superview
    mousePoint.x = MAX(0, MIN(mousePoint.x, self.bounds.size.width));
    mousePoint.y = MAX(0, MIN(mousePoint.y, self.bounds.size.height));

    // position is a custom ivar that indicates the center of the object;
    // you could also use frame.origin, but it looks nicer if objects are 
    // dragged from their centers
    myMovingRectangle.position = mousePoint;
    [self setNeedsDisplay:YES];
}

您将在 mouseUp: 中执行基本相同的边界检查。

更新:您还应该查看 View 编程指南，它会引导您创建可拖动 View :Creating a Custom View .

---

应该有用的示例代码，但与您的原始问题并不严格相关:

在 DotView.m 中:

- (void)drawRect:(NSRect)dirtyRect {
    // Ignoring dirtyRect for simplicity
    [[NSColor colorWithDeviceRed:0.85 green:0.8 blue:0.8 alpha:1] set];
    NSRectFill([self bounds]);
    // Dot is the custom shape class that can draw itself; see below
    // dots is an NSMutableArray containing the shapes
    for (Dot *dot in dots) {
        [dot draw];
    }
}

- (void)mouseDown:(NSEvent *)event {
    NSPoint mousePoint = [self convertPoint:[event locationInWindow] 
                             fromView:nil];

    currMovingDot = [self clickedDotForPoint:mousePoint];
    // Move the dot to the point to indicate that the user has
    // successfully "grabbed" it    
    if( currMovingDot ) currMovingDot.position = mousePoint;
    [self setNeedsDisplay:YES];
}

// -mouseDragged: already defined earlier in post

- (void)mouseUp:(NSEvent *)event {
    if( !currMovingDot ) return;

    NSPoint mousePoint = [self convertPoint:[event locationInWindow] 
                             fromView:nil];
    spot.x = MAX(0, MIN(mousePoint.x, self.bounds.size.width));
    spot.y = MAX(0, MIN(mousePoint.y, self.bounds.size.height));

    currMovingDot.position = mousePoint;
    currMovingDot = nil;
    [self setNeedsDisplay:YES];
}

- (Dot *)clickedDotForPoint:(NSPoint)point {
    // DOT_NUCLEUS_RADIUS is the size of the 
    // dot's internal "handle"
    for( Dot *dot in dots ){
        if( (abs(dot.position.x - point.x) <= DOT_NUCLEUS_RADIUS) &&
            (abs(dot.position.y - point.y) <= DOT_NUCLEUS_RADIUS)) {
            return dot;
        }
    }
    return nil;
}

点.h

#define DOT_NUCLEUS_RADIUS (5)

@interface Dot : NSObject {
    NSPoint position;
}

@property (assign) NSPoint position;

- (void)draw;

@end

点.m

#import "Dot.h"

@implementation Dot

@synthesize position;

- (void)draw {
    //!!!: Demo only: assume that focus is locked on a view.
    NSColor *clr = [NSColor colorWithDeviceRed:0.3 
                                         green:0.2 
                                          blue:0.8 
                                         alpha:1];
    // Draw a nice border
    NSBezierPath *outerCirc;
    outerCirc = [NSBezierPath bezierPathWithOvalInRect:
                         NSMakeRect(position.x - 23, position.y - 23, 46, 46)];
    [clr set];
    [outerCirc stroke];
    [[clr colorWithAlphaComponent:0.7] set];
    [outerCirc fill];
    [clr set];
    // Draw the "handle"
    NSRect nucleusRect = NSMakeRect(position.x - DOT_NUCLEUS_RADIUS,
                                    position.y - DOT_NUCLEUS_RADIUS,
                                    DOT_NUCLEUS_RADIUS * 2,
                                    DOT_NUCLEUS_RADIUS * 2);
    [[NSBezierPath bezierPathWithOvalInRect:nucleusRect] fill];
}

@end

如您所见，Dot 类非常轻量级，并使用贝塞尔曲线路径进行绘制。 super View 可以处理用户交互。