android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?这个错误，
很多通过activity生命周期来进行判断，这个不准确。
看错误，就是token为null，避免错误直接在调用showAtLocation showAsDropDown之前加个判断了，
就能解决了。
看PopupWindow源码：
public void showAtLocation(View parent, int gravity, int x, int y) {
mParentRootView = new WeakReference<>(parent.getRootView());
showAtLocation(parent.getWindowToken(), gravity, x, y);
}
public void showAsDropDown(View anchor) {
showAsDropDown(anchor, 0, 0);
}
public void showAsDropDown(View anchor, int xoff, int yoff) {
showAsDropDown(anchor, xoff, yoff, DEFAULT_ANCHORED_GRAVITY);
}
public void showAsDropDown(View anchor, int xoff, int yoff, int gravity) {
if (isShowing() || !hasContentView()) {
return;
}
TransitionManager.endTransitions(mDecorView);
attachToAnchor(anchor, xoff, yoff, gravity);
mIsShowing = true;
mIsDropdown = true;
final WindowManager.LayoutParams p =
createPopupLayoutParams(anchor.getApplicationWindowToken());
preparePopup(p);
final boolean aboveAnchor = findDropDownPosition(anchor, p, xoff, yoff,
p.width, p.height, gravity, mAllowScrollingAnchorParent);
updateAboveAnchor(aboveAnchor);
p.accessibilityIdOfAnchor = (anchor != null) ? anchor.getAccessibilityViewId() : -1;
invokePopup(p);
}
可以在传入对应view之前做个判断了
anchor.getApplicationWindowToken() ，或parent.getWindowToken() 判断是否为null， 不为null就在调用了弹出的方法。
