View的学习（一）

最新推荐文章于 2024-09-09 11:56:24 发布

原创最新推荐文章于 2024-09-09 11:56:24 发布 · 215 阅读

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自定义控件同时被 2 个专栏收录

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View的学习

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这篇博客介绍了Android中View的三个关键方法：requestLayout()用于触发重新布局，使视图在测量和布局阶段重新计算；invalidate()则强制视图重绘，执行onDraw()；而setMeasuredDimension()用于在onMeasure()中设置视图的测量宽度和高度，确保正确的尺寸。这些方法对于自定义视图的开发至关重要。

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本章主要讲述View的几个常用方法，对于后期自定义控件非常有用。

1、requestLayout()

在API文档中有这样的介绍：

Layout is a two pass process: a measure pass and a layout pass. The measuring pass is implemented in measure(int, int)......The second pass happens in layout(int, int, int, int)......

To intiate a layout, call requestLayout(). This method is typically called by a view on itself when it believes that is can no longer fit within its current bounds

因此，requestLayout()调用时，控件会重新执行 onMesure()和 onLayout()。

2、invalidate()

文档原话：To force a view to draw, call invalidate().

因此，invalidate()调用时，会执行onDraw()方法。

3、setMeasuredDimension (int measuredWidth, int measuredHeight)

文档说明：This method must be called by onMeasure(int, int) to store the measured width and measured height. Failing to do so will trigger an exception at measurement time.

该方法用于设置View的宽高，是在onMessure()调中执行（也就是说依赖于onMessure()）。因此，对于View的宽高更改，我们可以重写onMessure()，并用setMeasuredDimension ()进行设置