Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference

这是一个常见的错误，提示你在一个空对象上调用了findViewById方法。这个错误通常发生在以下情况下：

1. 在Activity的onCreate方法中调用findViewById方法之前，没有先使用setContentView方法设置布局文件；
2. findViewById方法的参数传递错误，导致找不到对应的View对象；
3. 调用了已经被销毁的View对象的findViewById方法。

你可以检查一下代码，看看是否存在以上情况。如果还无法解决问题，可以提供更多的代码和错误信息，我可以帮你进一步排查。

相关问题

lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getHeight()' on a null object reference

当你尝试在一个空对象上调用方法时，就会出现java.lang.NullPointerException异常。在这种情况下，你尝试在一个空的View对象上调用getHeight()方法，因此出现了'Attempt to invoke virtual method 'int android.view.View.getHeight()' on a null object reference'的错误信息。为了解决这个问题，你需要确保在调用方法之前，View对象不为空。你可以使用if语句来检查View对象是否为空，如果为空，则不要调用getHeight()方法。

以下是一个示例代码：

View view = findViewById(R.id.view_id);
if (view != null) {
    int height = view.getHeight();
    // do something with height
} else {
    // handle null view
}

Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference

This error message is typically caused by trying to call the setImageResource() method on an ImageView object that has not been initialized yet.

To resolve this error, you should make sure that you have properly initialized the ImageView object before trying to call any of its methods. This can be done by calling findViewById() to get a reference to the ImageView in your layout file and assigning it to a variable.

For example, if your ImageView has an id of "my_image_view" in your layout file, you could initialize it like this:

ImageView myImageView = findViewById(R.id.my_image_view);

Once you have properly initialized the ImageView object, you should be able to call its setImageResource() method without encountering the null object reference error.