如何使用 Jetpack Compose 显示在按钮单击时隐藏的 IconButton？

Question

I have in my ViewModel class, a State object with the default value of false .

var menuState = mutableStateOf(false)

Now I want to display the IconButton according to the value of menuState :

setContent {
    Scaffold(
        topBar = {
            TopAppBar (
                title = {
                    Text(
                        text = "MyApp",
                        fontSize = 18.sp
                    )
                    if (viewModel.menuState.value) { //Condition
                        IconButton(
                            onClick = {
                                //Do stuff
                            }
                        ) {
                            Icon(
                                imageVector = Icons.Outlined.MoreVert,
                                contentDescription = null,
                            )
                        }
                    }
                }
            )
        }
    )
}

This code works fine, when the app starts, since I want the IconButton to be hidden. Now the problem comes when I want to change the visibility from another composable on button click:

Button(
    onClick = {
        viewModel.menuState.value = true
    }
) {
    Text(
        text = "Sign out",
        fontSize = 18.sp
    )
}

Nothing happens. The IconButton remains hidden. How to solve this?

Answer 1

Try out this way:

Create Composable method for TopBar and pass boolean parameter

@Composable
fun TopBar(isVisible: Boolean) {
    TopAppBar (
        title = {
            Text(
                text = "MyApp",
                fontSize = 18.sp
            )
            if (isVisible) { //Condition
                IconButton(
                    onClick = {
                        //Do stuff
                    }
                ) {
                    Icon(
                        imageVector = Icons.Outlined.MoreVert,
                        contentDescription = null,
                    )
                }
            }
        }
    )
}

After that call this method:

setContent {
    Scaffold(
        topBar =  TopBar(viewModel.menuState.value)       }
    )
}