在NSView的drawRect:方法中，绘制一条线的首选/推荐方法是什么？

Question

在Cocoa的NSView层级中，我找不到任何线条绘制原语。唯一找到的是NSBezierPath。这是首选的方法吗？还是有其他我未发现的方法？

- eonil

Answer 1

NSBezierPath 是你应该使用的类。如果你只想从一个点到另一个点画一条直线，可以使用该类方法:

+strokeLineFromPoint:(NSPoint)point1 toPoint:(NSPoint)point2

- Rob Keniger

Answer 2

Cocoa 使用了一个隐式的绘图堆栈和无效模型。在您的 NSView 中，当状态更改导致视图绘制不同的时候，您需要调用 -[self setNeedsDisplay:] 来告诉绘图系统您需要被重新绘制。在非常近的将来，实际上是当前事件循环的末尾，将会调用您的视图的 drawRect: 方法。这是您绘制任何想要的内容的机会。

有一个隐式的焦点堆栈，这意味着当调用您的视图的 drawRect: 方法时，绘图将集中在并被裁剪到窗口中的视图边界。然后，您可以调用像 [[NSColor redColor] set]; 和 NSRectFill([self bounds]); 这样的函数。

下面是一个示例：

@interface MyView : NSView {
    @private
    NSColor *lineColor; 
    NSInteger clickCount;
}
@end

@implementation MyView
- (void)setLineColor:(NSColor *)color {
    if (color != lineColor) {
        [lineColor release];
        lineColor = [color copy];
        [self setNeedsDisplay:YES]; /// We changed what we'd draw, invalidate our drawing.
    }
}
- (void)mouseDown:(NSEvent *)mouseDown {
    clickCount = (clickCount == 6) ? 0 : (clickCount + 1);
    CGFloat hue = clickCount / 6.0; 
    [self setLineColor:[NSColor colorWithCalibratedHue:hue saturation:1.0 brightness:1.0 alpha:1.0]];
}

- (void)drawRect:(NSRect)dirtyRect {
    NSBezierPath *line = [NSBezierPath bezierPath];
    [line moveToPoint:NSMakePoint(NSMinX([self bounds]), NSMinY([self bounds]))];
    [line lineToPoint:NSMakePoint(NSMaxX([self bounds]), NSMaxY([self bounds]))];
    [line setLineWidth:5.0]; /// Make it easy to see
    [[self lineColor] set]; /// Make future drawing the color of lineColor.
    [line stroke];
}
@end

视图应该绘制一条对角线，每次单击时线条颜色都应更改。

- Jon Hess

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darRect方法中的第二个moveToPoint调用应该是lineToPoint调用。 - Jason Fuerstenberg

Answer 3

我尝试了Jon提供的示例，发现需要对上面的代码示例进行2个小修复。

1. 在init块中插入NSColor的分配器
2. 将第二个moveToPoint更改为lineToPoint

修复后，我发现这段代码非常有用。 注意：您可能还需要dealloc NSColor。

@interface PropertyPropagateView : NSView {
@private
    NSColor *lineColor; 
    NSInteger clickCount;  
}

@end


@implementation PropertyPropagateView

- (id)initWithFrame:(NSRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        lineColor=[NSColor blueColor];
    }

    return self;
}

- (void)dealloc
{
    [super dealloc];
}

- (void)setLineColor:(NSColor *)color {
    if (color != lineColor) {
        [lineColor release];
        lineColor = [color copy];
        [self setNeedsDisplay:YES]; /// We changed what we'd draw, invalidate our drawing.
    }
}
- (void)mouseDown:(NSEvent *)mouseDown {
    clickCount = (clickCount == 6) ? 0 : (clickCount + 1);
    CGFloat hue = clickCount / 6.0; 
    [self setLineColor:[NSColor colorWithCalibratedHue:hue saturation:1.0 brightness:1.0 alpha:1.0]];
}

- (void)drawRect:(NSRect)dirtyRect
{

    NSBezierPath *line = [NSBezierPath bezierPath];
    [line moveToPoint:NSMakePoint(NSMinX([self bounds]), NSMinY([self bounds]))];
    [line lineToPoint:NSMakePoint(NSMaxX([self bounds]), NSMaxY([self bounds]))];
    [line setLineWidth:5.0]; /// Make it easy to see
    [lineColor set]; /// Make future drawing the color of lineColor.

    [line stroke];
}

@end

- Ben

Answer 4

补充一些信息，我习惯在绘制前后保存和恢复图形状态，以保持操作的流畅性。

- (void)drawRect:(NSRect)dirtyRect {

    [[NSGraphicsContext currentContext] saveGraphicsState]

    NSBezierPath *line = [NSBezierPath bezierPath];
    [line moveToPoint:NSMakePoint(NSMinX([self bounds]), NSMinY([self bounds]))];
    [line lineToPoint:NSMakePoint(NSMaxX([self bounds]), NSMaxY([self bounds]))];
    [line setLineWidth:5.0]; /// Make it easy to see
    [[self lineColor] set]; /// Make future drawing the color of lineColor.
    [line stroke];

    [[NSGraphicsContext currentContext] restoreGraphicsState]

}

- Adrian Sluyters

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为什么这会让事情变得更快？ - Lawrence Kesteloot