如果不使用setContentView()，则发生NullPointerException的原因 [英] Reason for NullPointerException if setContentView() is not used

问题描述

我知道我们需要在初始化任何视图之前将setContentView()放在onCreate()方法中，否则它将引发空指针异常. 但这是什么原因?setContentView()与inflate()方法相似吗?

I know that we need to place setContentView() in the onCreate() method before initializing any view otherwise it will throw a null pointer exception. But what is the reason for it?Is the setContentView() similar to the inflate() method?

推荐答案

在初始化任何视图之前

before initializing any view

我不确定初始化任何视图"是什么意思.考虑到您剩下的问题，我将其解释为在活动中致电findViewById()".

I do not know for certain what you mean by "initializing any view". Given the rest of your question, I am going to interpret this as meaning "call findViewById() on the activity".

您需要先调用setContentView()，然后再调用findViewById()，因为否则将找不到小部件.

You need to call setContentView() before calling findViewById(), because otherwise there are no widgets to find.

setContentView()是否类似于inflate()方法?

Is the setContentView() similar to the inflate() method?

如果将布局资源ID传递给setContentView()方法，则

setContentView()将在其底下使用LayoutInflater和inflate().

setContentView() will use a LayoutInflater and inflate() under the covers, if you pass a layout resource ID into the setContentView() method.

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