  Measurements of the top--antitop quark pair production charge asymmetry in
the dilepton channel, characterized by two high-${p}_{\rm{T}}$ leptons
(electrons or muons), are presented using data corresponding to an integrated
luminosity of $20.3$ $\textrm{fb}^{-1}$ from $pp$ collisions at a
center-of-mass energy of $\sqrt{s} = 8$ TeV collected with the ATLAS detector
at the Large Hadron Collider at CERN. Inclusive and differential measurements
as a function of the invariant mass, transverse momentum, and longitudinal
boost of the $t\bar{t}$ system are performed both in the full phase space and
in a fiducial phase space closely matching the detector acceptance. Two
observables are studied: $A^{\ell\ell}_{\textrm{C}}$ based on the selected
leptons and $A^{t\bar{t}}_{\textrm{C}}$ based on the reconstructed $t\bar{t}$
final state. The inclusive asymmetries are measured in the full phase space to
be $A^{\ell\ell}_{\textrm{C}} = 0.008 \pm 0.006$ and $A^{t\bar{t}}_{\textrm{C}}
= 0.021 \pm 0.016$, which are in agreement with the Standard Model predictions
of $A^{\ell\ell}_{\textrm{C}} = 0.0064 \pm 0.0003 $ and
$A^{t\bar{t}}_{\textrm{C}} = 0.0111 \pm 0.0004$.
