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当使用按钮显示无法滚动this example（从角项目文档复制）时，项目不显示。使用ng-show显示无限滚动时不显示项目
如果ng-show=ctrl.show更改为ng-show=true，则显示这些项目。
为什么不用ng-show显示项目？
标记
<div ng-controller="AppCtrl as ctrl" ng-cloak="" class="virtualRepeatdemoInfiniteScroll" ng-app="MyApp">
<md-content layout="column">
<p>
Display an infinitely growing list of items in a viewport of only 7 rows (height=40px).
<br><br>
This demo shows scroll and rendering performance gains when using <code>md-virtual-repeat</code>;
achieved with the dynamic reuse of rows visible in the viewport area. Developers are required to
explicitly use <code>md-virtual-repeat-container</code> as a wrapping parent container.
<br><br>
To enable infinite scroll behavior, developers must pass in a custom instance of
mdVirtualRepeatModel (see the example's source for more info).
</p>
<button ng-click="ctrl.show=!ctrl.show" style="width:100px">Show</button>
<md-virtual-repeat-container id="vertical-container" ng-show=ctrl.show>
<div md-virtual-repeat="item in ctrl.infiniteItems" md-on-demand="" class="repeated-item" flex="">
{{item}}
</div>
</md-virtual-repeat-container>
</md-content>
</div>
JS
(function() {
'use strict';
angular
.module('MyApp')
.controller('AppCtrl', function($timeout) {
// In this example, we set up our model using a plain object.
// Using a class works too. All that matters is that we implement
// getItemAtIndex and getLength.
this.infiniteItems = {
numLoaded_: 0,
toLoad_: 0,
// Required.
getItemAtIndex: function(index) {
if (index > this.numLoaded_) {
this.fetchMoreItems_(index);
return null;
}
return index;
},
// Required.
// For infinite scroll behavior, we always return a slightly higher
// number than the previously loaded items.
getLength: function() {
return this.numLoaded_ + 5;
},
fetchMoreItems_: function(index) {
// For demo purposes, we simulate loading more items with a timed
// promise. In real code, this function would likely contain an
// $http request.
if (this.toLoad_ < index) {
this.toLoad_ += 20;
$timeout(angular.noop, 300).then(angular.bind(this, function() {
this.numLoaded_ = this.toLoad_;
}));
}
}
};
});
})();