Get Width and Height of a Widget

In Flutter, you can easily get the size of a specific widget after it’s rendered. What you need to do is to give it a key, then using that key to access currentContext.size property, like this:

// Full screen width and height
double width = MediaQuery.of(context).size.width;
double height = MediaQuery.of(context).size.height;

// Height (without SafeArea)
var padding = MediaQuery.of(context).padding;
double height1 = height - - padding.bottom;

// Height (without status bar)
double height2 = height -;

// Height (without status and toolbar)
double height3 = height - - kToolbarHeight;
        key: _key, 

Hoặc có thể sử dụng thư viện dart:ui

import 'dart:ui';