Null pointer exceptions that may be encountered in Android development

Record the null pointer exceptions encountered in Android development:

The first one is: the activity or service may not be defined in the Androidmanifest.xml, or the path is incorrectly written;

The second is: when the bundle is used, it may not be bound to the specified intent, while in the other activity to receive data, it will throw a null pointer exception!

The third is: when using Setcontentview in the activity, but also define some other layout buttons, when used, may throw a null pointer exception!