Java重绘()/更新()

Question

只是在编写一些与 java 图形相关的代码，这是我今天的讲座中的非常简单的示例。不管怎样，互联网似乎说更新不会被系统触发器调用，例如调整框架大小等。在这个例子中，更新是由这样的触发器调用的(因此当我只期望调用paint时，会调用update和paint) )。他似乎将其归因于操作系统以及每个操作系统的不同结果。

有人可以帮我澄清一下吗？

在 Windows 7 上工作

提前致谢

本

Answer 1

这是一篇精彩的文章，真正说明了一切:

http://java.sun.com/products/jfc/tsc/articles/painting/

1) Painting in AWT

To understand how AWT's painting API works, helps to know what triggers a paint operation in a windowing environment. In AWT, there are two kinds of painting operations: system-triggered painting, and application-triggered painting.

2) System-triggered Painting

In a system-triggered painting operation, the system requests a component to render its contents, usually for one of the following reasons:

• The component is first made visible on the screen.

• The component is resized.

• The component has damage that needs to be repaired. (For example, something that previously obscured the component has moved, and a previously obscured portion of the component has become exposed).

3) App-triggered Painting

In an application-triggered painting operation, the component decides it needs to update its contents because its internal state has changed. (For example,. a button detects that a mouse button has been pressed and determines that it needs to paint a "depressed" button visual).

4) The Paint Method

Regardless of how a paint request is triggered, the AWT uses a "callback" mechanism for painting, and this mechanism is the same for both heavyweight and lightweight components. This means that a program should place the component's rendering code inside a particular overridden method, and the toolkit will invoke this method when it's time to paint.