Bootstrap Modal with Chart.js linechart

I have a Twitter Bootstrap 3 Modal window and i want to draw an Chart.js linechart in it. But every time i open the modal the canvas element has a height and a width of 0. If i change these values the chart is empty. it seems like the chart is never drawn but i doesnt get any console output or errors. Modal: ``` <div class="modal fade" id="exampleModal" tabindex="-1" role="dialog" aria-labelledby="exampleModalLabel" aria-hidden="true"> <div class="modal-dialog"> <div class="modal-content"> <div class="modal-header"> <button type="button" class="close" data-dismiss="modal"><span aria-hidden="true">&times;</span><span class="sr-only">Close</span></button> <h4 class="modal-title" id="exampleModalLabel">New message</h4> </div> <div class="modal-body"> <p>Text</p> <canvas id="canvas" width="400" height="400"></canvas> <p>Text</p> </div> <div class="modal-footer"> <button type="button" class="btn btn-default" data-dismiss="modal">Close</button> </div> </div> </div> </div> ``` Javascript: ``` $('#exampleModal').on('show.bs.modal', function (event) { var button = $(event.relatedTarget); var modal = $(this); var canvas = modal.find('.modal-body canvas'); // Chart initialisieren var ctx = canvas[0].getContext("2d"); var chart = new Chart(ctx).Line({ labels: ["January", "February", "March", "April", "May", "June", "July"], datasets: [ { fillColor: "rgba(190,144,212,0.2)", strokeColor: "rgba(190,144,212,1)", pointColor: "rgba(190,144,212,1)", pointStrokeColor: "#fff", pointHighlightFill: "#fff", pointHighlightStroke: "rgba(220,220,220,1)", data: [65, 59, 80, 81, 56, 55, 40] }, { fillColor: "rgba(151,187,205,0.2)", strokeColor: "rgba(151,187,205,1)", pointColor: "rgba(151,187,205,1)", pointStrokeColor: "#fff", pointHighlightFill: "#fff", pointHighlightStroke: "rgba(151,187,205,1)", data: [65, 59, 80, 81, 56, 55, 40] } ] }, {}); }); ``` Button: ``` <button type="button" class="btn btn-primary" data-toggle="modal" data-target="#exampleModal" data-id="<?php echo $var["id"]; ?>">Open</button> ``` What is missing? Why the chart never gets drawn? Thanks