View.onDraw() --- 它什么时候被调用? [英] View.onDraw() --- when does it get called?

问题描述

我将 Log.d() 调用放入扩展视图的 onDraw() 中，因此我可以查看它被调用的频率和时间.它在视图的实例化时被调用，这并不奇怪.但后来我注意到，它在 onTouchEvent() 处理的每次点击时都会被调用，即使我的代码没有做任何与图形相关的远程操作.但是，在视图的文档中，我似乎无法找到有关 onDraw() 实际上是被调用的.我并不真正关心我在这里的特定项目(这对我来说没有问题)，我只想知道某处是否有列表或显示视图操作顺序的东西，特别是什么原因onDraw() 被调用.

I put a Log.d() call into the onDraw() of my extended View, so I could see how often and when it's getting called. It gets called upon instantiation of the view, which is not surprising. But then I notice, it gets called on every tap that is handled by onTouchEvent(), even though my code there isn't doing anything remotely related to graphics. However, in the documentation for Views, I can't seem to find anything about when onDraw() is actually called. I'm not really concerned about my particular project here (this doesn't cause a problem for me), I would just like to know if there is a list somewhere or something that shows the order of operations for a View, particularly what causes onDraw() to get called.

推荐答案

AFAIK，在以下情况下调用 View 的 onDraw():

AFAIK, a View's onDraw() is called when:

1. 初始绘制视图
2. 每当 invalidate() 被调用时在视图中

1. The view is initially drawn
2. Whenever invalidate() is called on the view

Invalidate 可以在需要时由您或系统调用.例如，许多视图会改变它们在触摸时的外观，例如 EditText 获得轮廓和光标，或者按钮处于按下状态.因此，视图会在触摸时重绘.

Invalidate can be called by you or the system whenever needed. For example, a lot of Views change how they look onTouch, like an EditText getting an outline and cursor, or a button being in the pressed state. Due to this, Views are redrawn on touch.

我同意最好有一份详细说明视图工作的文档，如果存在并且有人知道在哪里可以找到它，请告诉我们.

I agree that it would be nice to have a document that detailed the working of Views, and if one exists and somebody knows where to find it, please let us know.

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