NSImageView的图片正确的满屏放大缩小而没有黑边

NSImageView的时候,如果图片比View的边框小,图片会被放大以适应边框的大小。但是如果图片宽高比和View的宽高比不一致时,图片是不会填满整个View的,这个时候就会有黑边出现(不一定是黑色,根据View的背景色而定)。在iOS里可以选择UIViewContentModeScaleAspectFill来填满整个View,但是在Cocoa中是没有这个选项的。

所以我们应该调整图像大小以适应新大小，保持纵横比不变。如果图像小于新尺寸，则按比例放大并填充新帧。如果图像大于新尺寸，则缩小尺寸，并填充新框架。

- (NSImage*) resizeImage:(NSImage*)sourceImage size:(NSSize)size{

NSRect targetFrame = NSMakeRect(0, 0, size.width, size.height);
NSImage*  targetImage = [[NSImage alloc] initWithSize:size];

NSSize sourceSize = [sourceImage size];

float ratioH = size.height/ sourceSize.height;
float ratioW = size.width / sourceSize.width;

NSRect cropRect = NSZeroRect;
if (ratioH >= ratioW) {
    cropRect.size.width = floor (size.width / ratioH);
    cropRect.size.height = sourceSize.height;
} else {
    cropRect.size.width = sourceSize.width;
    cropRect.size.height = floor(size.height / ratioW);
}

cropRect.origin.x = floor( (sourceSize.width - cropRect.size.width)/2 );
cropRect.origin.y = floor( (sourceSize.height - cropRect.size.height)/2 );



[targetImage lockFocus];

[sourceImage drawInRect:targetFrame
               fromRect:cropRect       //portion of source image to draw
              operation:NSCompositeCopy  //compositing operation
               fraction:1.0              //alpha (transparency) value
         respectFlipped:YES              //coordinate system
                  hints:@{NSImageHintInterpolation:
 [NSNumber numberWithInt:NSImageInterpolationLow]}];

[targetImage unlockFocus];
return targetImage;
}



NSImage *newImg = [self resizeImage:@"原图" size:@"想要的大小"];

[aNSImageView setImage:newImg];