android动态设置组件LayoutParams

开发中经常用到动态设置组件的LayoutParams，之前开发遇到的问题如下：

	LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(width, height);
		params.gravity = Gravity.CENTER;
		params.leftMargin  = params.rightMargin = params.bottomMargin = params.topMargin = itemMagin;

<pre name="code" class="java">                gridView.setLayoutParams(params);

<span style="font-size:24px;color:#ff0000;background-color: rgb(51, 204, 0);">其中 </span><span style="font-family: Arial, Helvetica, sans-serif;"><span style="font-size:24px;color:#ff0000;background-color: rgb(51, 204, 0);">width 是屏幕的宽度</span>，设置后margin一直无效，修改如下</span>

<span style="font-family: Arial, Helvetica, sans-serif;"></span><pre name="code" class="java">
			LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(width, height);
			params.gravity = Gravity.CENTER;
			gridView.setPadding(itemMagin, itemMagin, itemMagin, itemMagin);
			gridView.setLayoutParams(params);

已padding设置即可正常