The acidity of halogens acids decrease in the order HI>HBr>HCl although their ionic characters increase in the reverse order.   

In other solvents, however, the strengths of these acids decrease in the order HI > HBr > HCl:  due to the decrease in the H-X bond energy in the order HCl > HBr > HI.

Ionic character increase in order HI< HBr < HCl due to increase in electronegativity of the halides in order                  I < Br < Cl.