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Bonjour.
Upon spending countless hours around this site looking for code to drag a component around the screen, I noticed an odd trend growing in the answers.
...being that everyone shudders at the sound of the null layout.
So I ask, what's the problem everyone has with it? I've been coding for no more than three months, using Swing for no more than one, and the layout has been a breeze to use with endless customisation possible. Why is it bad practice?
The major problem is the complexities involved in trying to make determination about individual platforms with regards to things like fonts and how pixels may be rendered
Even two systems, running the same OS can generate different output due to different hardware drivers and rendering pipelines.
Much of the API has been abstracted in such away that you should never care that one PC is using a DPI of 120 and using DirectX and another is using a DPI of 92 and using OpenGL.
Layout managers remove the developer from the responsibility of having to calculate the size a component (and its child components) at a particular moment in time as well as calculating the relationship between these components and does it in a standardised way.
The core Swing API has been designed to utilise this API, so when a component changes in some way that would represent a change in the size, all the required containers are notified automatically and the entire hierarchy of components can be adjusted as required.
The basic idea of a layout manager is to describe the relation between components on the same container as well as providing information about how much that container might like to have. This allows you to focus on the user-ability follow of the UI rather then trying to spend time trying to update the UI to meet all various possible combinations of hardware and software.
As a former VB developer (no, I'm not proud if it), I can assure you, the most frustrating part of working with it was trying to develop usable, dynamic UIs that didn't look crap on the next clients machine.
Of all the aspects of Swing, the layout management is one of the most welcomed - IMHO
Because it's not a layout. All you are doing is using a GUI editor to place your components in absolute locations. And resizing your window or running your code under a different monitor resolution will look terrible.
looking for code to drag a component around the screen
That is a different requirement. By definition when you drag a component around the screen you can't program the location.
Having said that a layout manager does more then just set the location of a component. Check out Drag Layout for a layout that you can still use in this situation.
For other situations a layout manager (or combination of nested layout managers) if the better solution for designing effective GUI's.
You will loose some points for GUI for using it, because it's hard to maintain, more code, less flexible,... Adding an extra button will lead to a lot of recalculation you have to do.
How i see it : http://leepoint.net/notes-java/GUI/layouts/nulllayout.html
来源：https://stackoverflow.com/questions/21242626/whats-wrong-with-the-null-layout-in-java