使用uni-app开发多端项目时，小程序中在子组件动态获取高度为null，但是在H5中就可以获取到

uni.getSystemInfo({
	 success: function (res) {
		let obj2 = uni.createSelectorQuery().select(".success_h");
		obj2.boundingClientRect(function (data) {
			console.log("itemHeight3", data);
			this.successHeight = data.height
		}).exec();
	},
});

打印“itemHeight3”小程序中为null，H5中就有值，经过一顿百度得知在小程序中需要用 in(this)

uni.getSystemInfo({
	success: function (res) {
		let obj2 = uni.createSelectorQuery().in(this).select(".success_h");
		obj2.boundingClientRect(function (data) {
			console.log("itemHeight3", data);
			this.successHeight = data.height
		}).exec();
	},
});