Today Extensionの高さの最大値の計算式

以下の式で計算できる。

iPhone:

float maxHeight = [[ UIScreen mainScreen ] bounds ].size.height - 126;

iPad:

float maxHeight = [[ UIScreen mainScreen ] bounds ].size.height - 171;

参考：

ios8 - Maximum height of iOS 8 Today Extension? - Stack Overflow