Why does Flutter need to have a "child: null" line of code when text button is used in a c-CodePudding

New to flutter. I'm currently working through a flutter course where I practice adding packages to play sounds by building a xylophone. When adding multiple buttons for each sound file, flutter was telling me "The parameter 'child' is required" and has me insert it at the end of the TextButton with a null property. The code worked fine without it on there but dart analysis kept giving me a warning. Sample code after inserting child listed below.

 children: [
                TextButton(
                  onPressed: () {
                    final player = AudioCache();
                    player.play('note1.wav');
                  },
                  style: ButtonStyle(
                    backgroundColor: MaterialStateProperty.all<Color>(Colors.red),
                  ), child: null,

I cannot seem to find why this was warning me but reading the documentation it looks like maybe because it was expecting text for text button? Can anyone explain or point to why it does this?

Thanks in advance.

CodePudding user response：

A TextButton should always have a child because if it doesn't it will not display anything, a text button can't size itself so it will always have the same size as its child, you need to put something on the child property or the text button will not know what to look like.

Now, you are passing null as the child, I will have to admit, I didn't think that was possible, I also don't think flutter likes this idea very much (If you activate null-safety, this code will throw a compile-time error). I think you should instead use Container, which is an empty-by-default widget as the child property:

TextButton(
  onPressed: () {
    final player = AudioCache();
    player.play('note1.wav');
  },
  style: ButtonStyle(
    backgroundColor: MaterialStateProperty.all<Color>(Colors.red),
  ),
  child: Container(),

You can also use the container with some color, some width or some height if you want:

Container(
  color: Colors.red,
  width: 20,
  height: 20,
);

CodePudding user response：

Your assumption is quite right. Its expecting a Widget ,if specific its expecting a TextWidget which consider a label or name of your button. Probably you're using an old version of flutter framework so its accepting null value of child but as I'm using 2.5.3 it's not accepting null value and you must need to provide it.