micmia micmia - 3 months ago 14
AngularJS Question

Maintain the scroll position when prepending content to a list (AngularJS)

I've been trying to prepend some items to a list within a scrollable container by using

ng-repeat
, and the recent one should be at the top of the list. I also need to maintain the scroll position if the scroll bar of the container is not at the very top when prepending content.

Here is my solution, but I still have a problem. There is always a flickering after angular has rendered prepended items in dom.



var myApp = angular.module('myApp', []);

myApp.controller('MainCtrl', function($scope, $interval, $timeout) {
$scope.items = [];
$interval(function() {
var item = {
id: Math.random(),
text: (new Date()).toString()
};
$scope.items.unshift.apply($scope.items, [item]);

var $container = $('.stream-container');
var $topItem = $('.item:first');
var oScrollTop = $container.scrollTop();
var oOffset = $topItem.length ? $topItem.position().top : 0;

$timeout(function() {
// Executed after the dom has finished rendering
if ($container.scrollTop() !== 0) {
$container.scrollTop(oScrollTop + ($topItem.length ? $topItem.position().top : 0) - oOffset);
}
});
}, 1000);
});

.stream-container {
overflow-y: scroll;
overflow-x: none;
height: 100px;
position: relative;
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<body ng-app="myApp">
<div class="stream-container" ng-controller="MainCtrl">
<div class="stream">
<div class="item" ng-repeat="item in items track by item.id">{{ item.text }}</div>
</div>
</div>
</body>




Answer

I found this post and changed $timeout to $scope.$$postDigest. Now it works as expected.

var myApp = angular.module('myApp', []);

myApp.controller('MainCtrl', function($scope, $interval, $timeout) {
  $scope.items = [];
  $interval(function() {
    var item = {
      id: Math.random(),
      text: (new Date()).toString()
    };
    $scope.items.unshift.apply($scope.items, [item]);

    var $container = $('.stream-container');
    var $topItem = $('.item:first');
    var oScrollTop = $container.scrollTop();
    var oOffset = $topItem.length ? $topItem.position().top : 0;

    $scope.$$postDigest(function() {
      // Executed after the dom has finished rendering
      if ($container.scrollTop() !== 0) {
        $container.scrollTop(oScrollTop + ($topItem.length ? $topItem.position().top : 0) - oOffset);
      }
    });
  }, 1000);
});
.stream-container {
  overflow-y: scroll;
  overflow-x: none;
  height: 100px;
  position: relative;
}
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<body ng-app="myApp">
  <div class="stream-container" ng-controller="MainCtrl">
    <div class="stream">
      <div class="item" ng-repeat="item in items track by item.id">{{ item.text }}</div>
    </div>
  </div>
</body>

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