安卓弹出键盘隐藏fixed定位相关的元素(obj必须是class)

//安卓弹出键盘隐藏fixed定位相关的元素(obj必须是class)
function displayFixed(obj){
    var h = document.body.scrollHeight;
    window.onresize = function(){
        if (document.body.scrollHeight < h) {
            document.getElementsByClassName(obj)[0].style.display = "none";
        }else{
            document.getElementsByClassName(obj)[0].style.display = "block";
        }
    };
}