Select checkbox from array values in AngularJS

I have created a page which contains some text boxes, radio buttons and check boxes. I am using this page to save new data or edit the existing one. I am able to save new data but for editing the data, the page should show some predefined values that it is getting from a variable. I am able to get and set the values for text boxes and radio buttons from that variable. But I am not able to check the check boxes. I have plenty of check boxes so I am using ng-repeat for the values to be displayed on page. I am setting the values of selected check boxes to an array and passing that value to my service layer.

Below are my code snippets:

HTML:

<div id="activityCheckboxList" class="checkboxList">
    <div ng-repeat="activity in activities">
        <label>
                <input type="checkbox" ng-true-value="activity" ng-checked="selection.indexOf(activity) > -1" ng-click="toggleSelection(activity)"/>
                <span>{{activity.activityName}}</span>
            </label>
    </div>
</div>

app.js:

$scope.selection=[];
$scope.getActivities(); //this sets values in $scope.activities which is a     list coming from service layer

    //Get Selected Activities from Check Boxes
    $scope.toggleSelection = function toggleSelection(activity){
        var idx = $scope.selection.indexOf(activity);

        if(idx > -1){
            $scope.selection.splice(idx, 1);
        }
        else{
            $scope.selection.push(activity);
        }
    };

After this, while clicking on submit, I am passing $scope.selection which will contain my activity objects.

For editing the data, I can put the data in selection[]. But how to check the check boxes using that and after that user should be uncheck/check them again. I tried using foreach loop but it didn't help.

Thanks in advance