CGContextRef不绘图

Question

我正在为我的Mac应用程序画一个圆圈。“守则”是：

- (void)mouseMoved:(NSEvent*)theEvent {
    NSPoint thePoint = [[self.window contentView] convertPoint:[theEvent locationInWindow] fromView:nil];
    NSLog(@"mouse moved: %f % %f",thePoint.x, thePoint.y);

    CGRect circleRect = CGRectMake(thePoint.x, thePoint.y, 20, 20);
    CGContextRef context = [[NSGraphicsContext currentContext] graphicsPort];
    CGContextSetRGBFillColor(context, 0, 0, 255, 1.0);
    CGContextSetRGBStrokeColor(context, 0, 0, 255, 0.5);
    CGContextFillEllipseInRect(context, CGRectMake(circleRect.origin.x, circleRect.origin.y, 25, 25));
    CGContextStrokeEllipseInRect(context, circleRect);
    [self needsDisplay];
}

- (void)mouseMoved:被完全调用，我可以在NSLog中看到正确的x和y坐标。但我没有任何圆..。令人惊讶的是:如果我是，最小化我的应用程序，重新打开它，(所以它“更新”NSView) ，那么这个圆圈就完美地绘制了！

Answer 1

mouseMoved是不适合绘制任何东西的地方，除非您是在屏幕外的缓冲区上绘图。如果要在屏幕上绘图，请保存thePoint和任何其他必要的数据，调用[self setNeedsDisplay:YES]并在drawRect:(NSRect)rect方法中绘制。

而且，我看不出有什么理由使用CGContextRef，而更多的是“友好”的NSGraphicsContext。不过，这是味道的问题。

绘图代码的一个示例：

- (void)mouseMoved:(NSEvent*)theEvent {
    // thePoint must be declared as the class member
    thePoint = [[self.window contentView] convertPoint:[theEvent locationInWindow] fromView:nil];
    [self setNeedsDisplay:YES];
}

- (void)drawRect:(NSRect)rect
{
    NSRect ovalRect = NSMakeRect(thePoint.x - 100, thePoint.y - 100, 200, 200);
    NSBezierPath* oval = [NSBezierPath bezierPathWithOvalInRect:ovalRect];
    [[NSColor blueColor] set];
    [oval fill];
    [[NSColor redColor] set];
    [oval stroke];
}