操纵Cell和Control

本文包含用于处理Cell和Control的其他技巧和示例。

设置Cell或Control的大小

要将Cell（以及任何封闭的只有一个Cell的Control）的大小设置为符合人机界面准则的最佳大小，请执行以下操作：

  1. 如果Cell包含文本，请将文本的字体设置为与以下三种标准大小之一一致：regular，small和mini。为此，请使用NSFont类方法systemFontSizeForControlSize:。该方法的参数是NSControl类声明的NSControlSize常量。
  1. float fontSize = [NSFont systemFontSizeForControlSize:NSMiniControlSize];
  2. NSCell *theCell = [theControl cell];
  3. NSFont *theFont = [NSFont fontWithName:[[theCell font] fontName] size:fontSize];
  4. [theCell setFont:theFont];
  1. 使用相同的常数将Control大小设置为与字体大小相同的大小。使用NSControl的setControlSize:方法。
  1. [theCell setControlSize:NSMiniControlSize];
  1. 最后，将sizeToFit发送到Control以修剪额外的宽度。
  1. [theControl sizeToFit];

在Cell边界内绘制聚焦环

The NSSetFocusRingStyle sets the style that a focus ring will be drawn in the next time you fill a bezier path. It takes a constant of type of NSFocusRingPlacement to tell the Application Kit to draw the focus ring over an image, under text, or (when neither text or image is a consideration) around a shape. You can use this function with a constant of NSFocusRingOnly to draw a focus ring just inside a cell’s bounds.

Listing 1 shows how you draw such a focus ring. It requires you to override the NSCell drawWithFrame:inView:. In this method, if the cell is supposed to draw evidence of first-responder status, set the rectangle for the focus ring, call NSSetFocusRingStyle with an argument of NSFocusRingOnly, and then create and fill a bezier path defining that rectangle. Filling in this case simply draws the ring.

Note: This technique requires you to subclass a cell class. See “Subclassing NSCell” for information.

Listing 1 Drawing a focus ring just inside a cell’s bounds

  1. - (void)drawWithFrame:(NSRect)cellFrame inView:(NSView *)controlView {
  2.     // other stuff might happen here
  3.     if ([self showsFirstResponder]) {
  4.          // showsFirstResponder is set for us by the NSControl that is drawing  us.
  5.         NSRect focusRingFrame = cellFrame;
  6.         focusRingFrame.size.height -= 2.0;
  7.         [NSGraphicsContext saveGraphicsState];
  8.         NSSetFocusRingStyle(NSFocusRingOnly);
  9.         [[NSBezierPath bezierPathWithRect: NSInsetRect(focusRingFrame,4,4)] fill];
  10.         [NSGraphicsContext restoreGraphicsState];
  11.     }
  12.      // other stuff might happen here
  13. }

在Cell内放置图像

如果Cell显示的是图像而不是文本（或除文本之外也显示图像），则可以通过覆盖imageRectForBounds:方法来影响图像在Cell中的放置，该方法由NSCell和NSMenuItemCell类都声明。此方法返回绘制Cell图像的矩形，通常是一个稍微偏离Cell边界的矩形。例2给出了一个示例。

注意： 此技术要求你将Cell类子类化。有关信息，请参见“对NSCell进行子类化”。

例2 将图像居中放置在Cell中

  1. - (NSRect) imageRectForBounds:(NSRect)theBounds {
  2.     NSRect r = theBounds;
  3.     // get size. If no image, result of method returning NSSize is undefined so assume NSZeroSize
  4.     NSSize imageSize = [self image] != nil ? [[self image] size] : NSZeroSize;
  5.     r.origin.x = floor((r.size.width/2)  - (imageSize.width/2)  + 0.5);
  6.     r.origin.y = floor((r.size.height/2) - (imageSize.height/2) + 0.5);
  7.     r.size     = imageSize;
  8.     return r;
  9. }

在此示例中，Cell将图像居中。请注意，它会将返回值四舍五入到最接近的像素，以避免使用部分像素偏移可能导致的绘图模糊。该代码还将返回的矩形的size字段设置为图像的大小，以便在矩形中正确绘制（假设NSImage对象使用drawInRect:fromRect:operation:fraction:进行绘制，而不使用compositeToPoint:operation:）。