安卓系统中的ViewTreeObserver NullPointerException崩溃

View myView = findViewById(R.id.my_view);
if (myView != null && myView.getWindowToken() != null) {
    ViewTreeObserver observer = myView.getViewTreeObserver();
    observer.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
        @Override
        public void onGlobalLayout() {
            // 执行相关操作
        }
    });
}

new Handler(Looper.getMainLooper()).post(new Runnable() {
    @Override
    public void run() {
        View myView = findViewById(R.id.my_view);
        if (myView != null) {
            ViewTreeObserver observer = myView.getViewTreeObserver();
            observer.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
                @Override
                public void onGlobalLayout() {
                    // 执行相关操作
                }
            });
        }
    }
});

ViewTreeObserver observer = myView.getViewTreeObserver();
final ViewTreeObserver.OnGlobalLayoutListener listener = new ViewTreeObserver.OnGlobalLayoutListener() {
    @Override
    public void onGlobalLayout() {
        // 执行相关操作
        // 完成后移除监听器
        myView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
    }
};
observer.addOnGlobalLayoutListener(listener);