isInEditMode:
Indicates whether this View is currently in edit mode. A View is usually in edit mode when displayed within a developer tool. For instance, if this View is being drawn by a visual user interface builder, this method should return true. Subclasses should check the return value of this method to provide different behaviors if their normal behavior might interfere with the host environment. For instance: the class spawns a thread in its constructor, the drawing code relies on device-specific features, etc. This method is usually checked in the drawing code of custom widgets.
如果在自定义控件的构造函数或者其他绘制相关地方使用系统依赖的代码，会导致可视化编辑器无法报错并提示：Use View.isInEditMode() in your custom views to skip code when shown in Eclipse
比如：
public class LockRelativeLayout extends RelativeLayout {
private Handler mainHandler = null; //与主Activity通信的Handler对象
public LockRelativeLayout(Context context, AttributeSet attrs) {
super(context, attrs, 0);
mContext = context;
if (isInEditMode()) { return; }
mainHandler = ((SPActivity)mContext).getMHandler();
}
}
如果不加上if (isInEditMode()) { return; }，标红处代码会导致可视化编辑报错