\(\triangle ABC\)中,角\(A\),\(B\),\(C\)的对边分别为\(a\),\(b\),\(c\),已知\( \dfrac { \sqrt {3}\sin C}{\cos B}= \dfrac {c}{b}\).
\((\)Ⅰ\()\)求角\(B\)的大小;
\((\)Ⅱ\()\)点\(D\)为边\(AB\)上的一点,记\(∠BDC=θ\),若\( \dfrac {π}{2} < θ < π\),\(CD=2\),\(AD= \sqrt {5}\),\(a= \dfrac {8 \sqrt {5}}{5}\),求\(\sin θ\)与\(b\)的值.