这个:当前类对象

getContext():返回当前活动的上下文

getApplicationContext():返回应用程序中正在运行的所有活动

从这个文档

我明白你应该用:

尝试使用上下文应用程序而不是上下文活动

getApplicationContext()——返回应用程序中运行的所有活动的上下文。

getBaseContext()—当您想要从您可以访问的应用程序中的另一个上下文访问Context时。

getContext()——它只返回当前正在运行的活动的上下文视图。

This - it's引用当前类对象

它引用当前活动类对象，而活动继承上下文，因此必须在可以使用上下文或活动的地方使用它。

View.getContext(): Returns the context the view is currently running in. Usually the currently active Activity. Activity.getApplicationContext(): Returns the context for the entire application (the process all the Activities are running inside of). Use this instead of the current Activity context if you need a context tied to the lifecycle of the entire application, not just the current Activity. ContextWrapper.getBaseContext(): If you need access to a Context from within another context, you use a ContextWrapper. The Context referred to from inside that ContextWrapper is accessed via getBaseContext().

大多数答案已经涵盖了getContext()和getApplicationContext()，但很少解释getBaseContext()。

getBaseContext()方法只在你有一个contexttwrapper时才有用。 Android提供了一个ContextWrapper类，它是围绕一个现有的Context创建的，使用:

ContextWrapper wrapper = new ContextWrapper(context);

使用ContextWrapper的好处是，它允许你“在不改变原始上下文的情况下修改行为”。例如，如果你有一个名为myActivity的活动，那么可以创建一个与myActivity主题不同的视图:

ContextWrapper customTheme = new ContextWrapper(myActivity) {
  @Override
  public Resources.Theme getTheme() { 
    return someTheme;
  }
}
View myView = new MyView(customTheme);

ContextWrapper is really powerful because it lets you override most functions provided by Context including code to access resources (e.g. openFileInput(), getString()), interact with other components (e.g. sendBroadcast(), registerReceiver()), requests permissions (e.g. checkCallingOrSelfPermission()) and resolving file system locations (e.g. getFilesDir()). ContextWrapper is really useful to work around device/version specific problems or to apply one-off customizations to components such as Views that require a context.

getBaseContext()方法可用于访问ContextWrapper所包装的“基本”上下文。你可能需要访问“base”上下文，例如，检查它是一个服务，活动还是应用程序:

public class CustomToast {
  public void makeText(Context context, int resId, int duration) {
    while (context instanceof ContextWrapper) {
      context = context.baseContext();
    }
    if (context instanceof Service)) {
      throw new RuntimeException("Cannot call this from a service");
    }
    ...
  }
}

或者如果你需要调用一个方法的“unwrapped”版本:

class MyCustomWrapper extends ContextWrapper {
  @Override
  public Drawable getWallpaper() {
    if (BuildInfo.DEBUG) {
      return mDebugBackground;
    } else {
      return getBaseContext().getWallpaper();
    }
  }
}

上下文为新创建的组件提供有关活动或应用程序的信息。

应该为新创建的组件提供相关上下文(无论是应用程序上下文还是活动上下文)

因为Activity是Context的子类，所以可以使用它来获取Activity的上下文