利用WeakReference

private NoLeakHandler mHandler = new NoLeakHandler(this);

private static class NoLeakHandler extends Handler {
	private WeakReference<PayActivity> mActivity;

	NoLeakHandler(PayActivity activity) {
		mActivity = new WeakReference<>(activity);
	}

	@Override
	public void handleMessage(Message msg) {
		PayActivity payActivity = mActivity.get();
		//...
	}
}


===========

private Permission mPermission = new Permission(this);

public static class Permission{
	private Activity mAty;

	Permission(Activity activity) {
		mAty = new WeakReference<>(activity).get();
	}
	//...
}