WPF - 调整儿童填充父母的大小

In WPF, I simply want to have a 'container' which has 3 textblocks. I would like these 3 textblocks to be sized so they each take up 1/3 of the parent's width. I noticed that the stackpanel sizes the last child automatically, but is there a way to size each child automatically?In WPF, I simply want to have a 'container' whi