开关盒内部有条件断开

Question

我想知道是否有可能在C#中的switch语句中有条件地突破一个案例.以下面的例子为例.

MediaStream photoMediaStream = null;
switch (photoSize)
{
    case PhotoSize.Normal:
        if (imageWidth >= NormalWidth && imageWidth % NormalWidth == 0)
        {
            photoMediaStream = photoMedia.GetStream(new MediaOptions {Width = NormalWidth});
            break;
        }
    case PhotoSize.Small:
        if (imageWidth >= SmallWidth && imageWidth % SmallWidth == 0)
        {
            photoMediaStream = photoMedia.GetStream(new MediaOptions {Width = SmallWidth});
            break;
        }
    case PhotoSize.Thumb:
        if (imageWidth >= ThumbWidth && imageWidth % ThumbWidth == 0)
        {
            photoMediaStream = photoMedia.GetStream(new MediaOptions {Width = ThumbWidth});
            break;
        }
}

基本上,如果条件为真,我想做一些事情,然后突破switch语句,但如果不是,我只想进入下一个案例.

Answer 1

由于您无法隐式进入下一个案例,因此必须使用该goto语句显式执行此操作.这是可以接受使用此声明的罕见情况之一......

MediaStream photoMediaStream = null;
switch (photoSize)
{
    case PhotoSize.Normal:
        if (imageWidth >= NormalWidth && imageWidth % NormalWidth == 0)
        {
            photoMediaStream = photoMedia.GetStream(new MediaOptions {Width = NormalWidth});
            break;
        }
        goto case PhotoSize.Small;
    case PhotoSize.Small:
        if (imageWidth >= SmallWidth && imageWidth % SmallWidth == 0)
        {
            photoMediaStream = photoMedia.GetStream(new MediaOptions {Width = SmallWidth});
            break;
        }
        goto case PhotoSize.Thumb;
    case PhotoSize.Thumb:
        if (imageWidth >= ThumbWidth && imageWidth % ThumbWidth == 0)
        {
            photoMediaStream = photoMedia.GetStream(new MediaOptions {Width = ThumbWidth});
            break;
        }
}

无论如何,使用if语句重构它可能会更好:

MediaStream GetPhotoMediaStream(PhotoSize photoSize, /* whatever parameters you need... */)
{
    if (photoSize == PhotoSize.Normal)
    {
        if (imageWidth >= NormalWidth && imageWidth % NormalWidth == 0)
        {
            return photoMedia.GetStream(new MediaOptions {Width = NormalWidth});
        }
        photoSize = PhotoSize.Small;
    }
    if (photoSize == PhotoSize.Small)
    {
        if (imageWidth >= SmallWidth && imageWidth % SmallWidth == 0)
        {
            return photoMedia.GetStream(new MediaOptions {Width = SmallWidth});
        }
        photoSize = PhotoSize.Thumb;
    }
    if (photoSize == PhotoSize.Thumb)
    {
        if (imageWidth >= ThumbWidth && imageWidth % ThumbWidth == 0)
        {
            return photoMedia.GetStream(new MediaOptions {Width = ThumbWidth});
        }
    }
    return null;
}