EDIT

The docs specify that you need to wrap your keys in quotation marks so they aren't invalid JSON object keys:

return {
     "background-color": taskType.backColor,
     "color": taskType.color,
     "font-size":taskType.fontSize,
     "font-family":taskType.font
}

Old Answer (not using ng-style)  正确答案

While I never used ng-style, it doesn't seem to take objects. Rather it is an equivalent of ng-class but for single styles.

Try changing your function to:

$scope.getStyle = function (taskType) {

        return {
         "background-color:"+taskType.backColor+
         ";color:"+ taskType.color+
         ";font-size:"+taskType.fontSize+
         ";font-family:"+taskType.font+";";
    }
)};

and the html to use the regular style tag with a bind:

<div class="form-control" id="data.objectStyle"  
ng-model="data.type" style="{{getStyle(data.objectStyle)}}">