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By adopting the codes I got from the previous questions, here I intend to adjust the vertices positions of a RandomGraph. However, I only got an inactive graph, it even disappears suddenly when clicking on it. Again, what is wrong in these codes?

DynamicModule[{p, ind , vpos, VPOS},
rg = RandomGraph[{#, # + 4}] & [ RandomInteger[{5, 7}]];
edglst = EdgeList[rg];
vlst = VertexList[rg];
vcoord = VertexCoordinates /. AbsoluteOptions[rg, VertexCoordinates];

(vpos[#] = #2) & @@@ MapThread[UndirectedEdge, {vlst, vcoord}];
VPOS = Table[vpos[i], {i, vlst}];

EventHandler[ 
gg = Dynamic@
    Graph[vlst, edglst, VertexCoordinates -> VPOS, VertexSize -> 0.08,
      VertexLabels -> "Name", PlotRange -> All, EdgeStyle -> {Thick}, 
     ImagePadding -> 10 ],

  {"MouseDown" :> 
    With[{ set = VPOS , pos = MousePosition["Graphics"]}, 
     ind = Position[set  , Nearest[set  , pos][[1]]][[1, 1]]],

   "MouseDragged" :> (ReleaseHold[
      Hold[Set][Hold[VPOS][[{1}, ind]], MousePosition["Graphics"]]])} 
  ]
]

Following Kguler's suggestion, I found that the above code works fine just by changing the MouseDragged statement to m_goldberg's way, and followed by PassEventsDown -> True. Why setting PassEventDown to True is that crucial?

DynamicModule[{p, ind, vpos, VPOS}, 
 rg = RandomGraph[{#, # + 4}] &[RandomInteger[{5, 7}]];
 edglst = EdgeList[rg];
 vlst = VertexList[rg];
 vcoord = VertexCoordinates /. AbsoluteOptions[rg, VertexCoordinates];
 (vpos[#] = #2) & @@@ MapThread[UndirectedEdge, {vlst, vcoord}];
 VPOS = Table[vpos[i], {i, vlst}];
 EventHandler[
   gg = Dynamic@
   Graph[vlst, edglst, VertexCoordinates -> VPOS, VertexSize -> 0.08,
   VertexLabels -> "Name", PlotRange -> All, EdgeStyle -> {Thick}, 
   ImagePadding -> 10], {"MouseDown" :> 
     With[{set = VPOS, pos = MousePosition["Graphics"]}, 
      ind = Position[set, Nearest[set, pos][[1]]][[1, 1]]], 
      "MouseDragged" :> ( VPOS [[ ind]] = MousePosition["Graphics"]  )}, 
      PassEventsDown -> True
  ]
]
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  • $\begingroup$ In this case it will be better to use method introduced by m_goldberg in your previous question. This one was provided to deal with a few named positions not an array. $\endgroup$ – Kuba♦ Jun 24 '14 at 21:36
  • $\begingroup$ I did tried m_goldberg's code, replaced the "MouseDragged" statement as below, it didn't work neither. "MouseDragged" :> (VPOS[[ind]] = MousePosition["Graphics"] $\endgroup$ – Putterboy Jun 24 '14 at 21:51
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Using @m-goldberg's code in the linked Q/A for handling mouse events and rescaling the vertex coordinates of the initial random graph:

DynamicModule[{index = 1, vertxCoords, rg}, 
  rg = RandomGraph[{#, # + 4}] &[RandomInteger[{5, 7}]]; 
  vertxCoords = (VertexCoordinates /. AbsoluteOptions[rg, VertexCoordinates]);
  vertxCoords =  Rescale[#, 1 + Through[{Min, Max}[vertxCoords]], {0, 1}] & /@ 
             vertxCoords;
  EventHandler[
   Dynamic@Graph[EdgeList[rg], VertexCoordinates -> vertxCoords, 
    VertexSize -> {.04, .04}, VertexLabels -> "Name", PlotRange -> 1, 
    EdgeStyle -> Thick, Frame -> True], 
  {"MouseDown" :>  With[{p = MousePosition["Graphics"]}, 
          index = Position[vertxCoords, Nearest[vertxCoords, p][[1]]][[1, 1]]], 
   "MouseDragged" :> (vertxCoords[[index]] =  MousePosition["Graphics"])},
  PassEventsDown -> True]]

enter image description here

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