强制转换结果findViewById android方法 [英] Cast result findViewById android method

问题描述

为什么我们总是必须强制转换方法findViewById(id)返回的值?正如我在Google参考中看到的那样，该方法已经返回了一个视图:

Why do we always have to cast the value returned by the method findViewById(id) ? The method already returns a view, as I've seen in google reference :

http://developer.android.com/reference/android/view/View.html#findViewById(int)

那么是否有可能将其他事物从视图中分离出来?例如，执行以下操作:

Then is it possible to cast to another thing apart form a view ? For example, do this :

ImageView image = (ImageView) findViewById(R.id.image) ?

推荐答案

方法findViewById()返回实际上用于在XML文件中定义该视图的类的实例.方法签名返回View以使其通用且可用于所有为View继承的类.

The method findViewById() returns an instance of the class that is actually used to define that view in your XML file. The method signature returns a View to make it generic and usable for all classes that inherit for View.

像使用变量一样，您需要将返回值强制转换为定义了变量的类:

You need to cast the returned value to the class that your variable is defined when you use it like:

ImageView image = (ImageView) findViewById(R.id.image);

Java不会为您隐式强制转换.

Java won't cast that implicitly for you.

您可以将其保留为:

View image = findViewById(R.id.image);

，但是您将无法使用在ImageView类上定义的方法等.

but you wouldn't be able to use the methods, etc. defined on ImageView class.

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