Display function value on hover?

Question

I have used Manipulate in conjunction with Plot to draw a function's graph and I would like to show the current x-axis value and function value while hovering over the function's plot. How can I achieve this?

Thanks.

Answer 1

Manipulate[
 Module[{tbl},
  tbl = Table[Tooltip[{x, Sin[a x]}], {x, -Pi, Pi, .1}];
  ListLinePlot[tbl, Mesh -> All, MeshStyle -> Opacity[0]]
  ],
 {{a, 1, "a?"}, .1, 5, .1}
 ]

Answer 2

Alternative that avoids the flicker of Tooltip (copying & adapting @Nasser):

f[x_, a_] := Sin[a x^3];
p = {0, 0};
Manipulate[
 EventHandler[
  Plot[f[x, a], {x, -Pi, Pi}, 
   Prolog -> Dynamic@{Thin, 
       Line[{{p[[1]], 0}, {p[[1]], f[ p[[1]], a]}, {0, f[ p[[1]], a]}}], 
       Point[{p[[1]], f[ p[[1]], a]}]}, 
   PlotLabel -> 
    Dynamic@{p[[1]], f[ p[[1]], a]}],
  {"MouseMoved" :> (p = If[# =!= None, #, p] &@MousePosition["Graphics"])}],
{{a, 1, "a?"}, .1, 5, .1}]

It also takes advantage of Plot's adaptive graphing methods to deal with wiggly graphs.