objective-c - NSImageView 绘制不正确

Question

我创建了一个 NSView 的自定义子类来控制 2 个 NSImageView。创建图像的代码如下:

- (id)initWithFrame:(NSRect)frameRect AndMap:(NSImage *)map AndPlayer:(NSImage *)guyImage
{
    self = [super initWithFrame:frameRect];
    if (self)
    {
        NSRect newRect = NSMakeRect(0.0, 0.0, 64.0, 64.0);

        NSImageView *theMap = [[NSImageView alloc] initWithFrame:NSMakeRect(0.0, 0.0, frameRect.size.width, frameRect.size.height)];
        [theMap setImage:map];

        NSImageView *theGuy = [[NSImageView alloc] initWithFrame:newRect];
        [theGuy setImage:guyImage];

        [self setMapImage:theMap];
        [self setPlayerView:theGuy];
        [self addSubview:[self mapImage]];
        [self addSubview:[self playerView]];

但是，当我告诉 View 在原点为 (128,0) 的矩形中绘制时，它会以奇怪的偏移量绘制 theMap ，因此 theGuy 的原点位于 128,0，但theMap 的原点类似于 (128,20)。我找不到发生这种情况的任何原因。

Answer 1

我的猜测是您有重叠的同级 View :

• theMap 具有框架 {{0.0, 0.0}, {frameRect.size.width, frameRect.size.height}}
• theGuy 具有框架 {{0.0, 0.0}, {64.0, 64.0}}
• theMap 和 theGuy 都(或似乎)添加到同一个 super View ，即 self 中，并且具有相同的起源。

Cocoa 不保证重叠同级 View 的正确行为，即两个 View 具有相同的直接父 View 并且其相应的帧重叠。来自 View Programming Guide :

Note: For performance reasons, Cocoa does not enforce clipping among sibling views or guarantee correct invalidation and drawing behavior when sibling views overlap. If you want a view to be drawn in front of another view, you should make the front view a subview (or descendant) of the rear view.

根据this answer to another question on Stack Overflow ，一种替代解决方案是打开 View 的图层。