通过鼠标事件绘制到 NSView

Question

我是编程、objective-c（和 stackoverflow）的新手。我正在学习并非常缓慢地前进；）但后来我遇到了一个问题，谷歌无法解决。我有一个窗口和一个 NSview，然后添加了一个鼠标事件，应该将坐标绘制到我的视图中，但它没有。有趣的是：它是在鼠标移到我的应用程序窗口的窗口按钮上时绘制的...

- (void)drawRect:(NSRect)dirtyRect {
   NSPoint imagePos = NSMakePoint(0, 0);
   NSImage *aImage = [NSImage imageNamed:@"mw_bg01.png"];
   [aImage dissolveToPoint:imagePos fraction:1.0];
}
- (void)mouseDown:(NSEvent*)theEvent;{
   mouseLoc = [NSEvent mouseLocation];
   mousePosX = mouseLoc.x;mousePosY = mouseLoc.y;
   NSString* mouseString = [NSString stringWithFormat:@"%d", mousePosX];
   NSPoint textPoint = NSMakePoint(5, 5);
   NSMutableDictionary *textAttrib = [[NSMutableDictionary alloc] init];
   [textAttrib setObject:[NSFont fontWithName:@"Helvetica Light" size:10]
               forKey:NSFontAttributeName];
   [textAttrib setObject:[NSColor grayColor] forKey:NSForegroundColorAttributeName];
   [mouseString drawAtPoint:textPoint withAttributes:textAttrib];
}

我不知道该怎么做，有什么建议吗？谢谢！

Answer 1

您不应该在-mouseDown: 方法中进行绘图。相反，您必须在-drawRect:（或从-drawRect: 调用的方法）中完成所有绘图。试试这样的：

@interface MyView ()
    @property NSPoint lastMousePoint;
@end

@implementation MyView

- (void)drawLastMousePoint
{
    NSString *mouseString = NSStringFromPoint(self.lastMousePoint);
    NSPoint textPoint = NSMakePoint(5, 5);
    NSMutableDictionary *textAttrib = [[NSMutableDictionary alloc] init];
    [textAttrib setObject:[NSFont fontWithName:@"Helvetica Light" size:10]
                forKey:NSFontAttributeName];
    [textAttrib setObject:[NSColor grayColor] forKey:NSForegroundColorAttributeName];
    [mouseString drawAtPoint:textPoint withAttributes:textAttrib];
}

- (void)drawRect:(NSRect)dirtyRect 
{
    NSPoint imagePos = NSMakePoint(0, 0);
    NSImage *aImage = [NSImage imageNamed:@"mw_bg01.png"];
    [aImage dissolveToPoint:imagePos fraction:1.0];

    [self drawLastMousePoint];
}

- (void)mouseDown:(NSEvent*)theEvent;
{
    self.lastMousePoint = [theEvent locationInWindow];
    [self setNeedsDisplay:YES];
}

@end

当您收到鼠标按下事件时，您只需存储鼠标按下的位置。绘图是在 -drawLastMousePoint 中完成的，您可以在 -drawRect: 方法中调用它。由于您知道在任何时候单击鼠标都需要重绘，因此您调用-setNeedsDisplay: 通知视图它需要重绘。请注意，重绘不会立即发生，而是会在下一次通过运行循环时发生。换句话说，您是在说“嘿，发生了一些变化，我需要重新绘制视图的内容。请尽快再次致电-drawRect:！”

另一个注意事项：+[NSEvent mouseLocation] 真正设计用于获取当前鼠标位置在事件流之外。通常，在-mouseDown: 方法中，您在作为参数传递给该方法的NSEvent 上调用-locationInWindow。如果需要转换为本地/视图坐标，请致电[self convertPoint:[theEvent locationInWindow] fromView:nil];。