[dashboard] load list of slices at modal enter time (#3379)

superset/assets/javascripts/dashboard/components/SliceAdder.jsx

@@ -37,7 +37,11 @@ class SliceAdder extends React.Component {
     };
   }
 
-  componentDidMount() {
+  componentWillUnmount() {
+    this.slicesRequest.abort();
+  }
+
+  onEnterModal() {
     const uri = '/sliceaddview/api/read?_flt_0_created_by=' + this.props.dashboard.curUserId;
     this.slicesRequest = $.ajax({
       url: uri,
@@ -66,10 +70,6 @@ class SliceAdder extends React.Component {
     });
   }
 
-  componentWillUnmount() {
-    this.slicesRequest.abort();
-  }
-
   addSlices() {
     this.props.dashboard.addSlicesToDashboard(Object.keys(this.state.selectionMap));
   }
@@ -173,6 +173,7 @@ class SliceAdder extends React.Component {
       <ModalTrigger
         triggerNode={this.props.triggerNode}
         tooltip="Add a new slice to the dashboard"
+        beforeOpen={this.onEnterModal.bind(this)}
         isButton
         modalBody={modalContent}
         bsSize="large"