将 lambda 函数从 java 类传递到 kotlin 类给了我错误

Question

My kotlin class:

class InstallationReceiver(activity : RootActivity, url : String, progressCallback : 
((percentage : Int) -> Unit)?,  callback : ((isUpdated : Boolean) -> Unit)?, packageName: 
String){

//my code

}

I am passing lambda fun to this class from java class like this:

new InstallationReceiver(getActivity(), apkUrl, integer -> **{ 
String text = "Installing app"+integer;
textView.setText(text);
}**,true,null);

Why this lambda function is demanding a Unit return type?. I even tried returning Unit.INSTANCE but nothing helped me out. It's still showing error.

Answer 1

What are those asterisks?
I tried this minimal example and it works:

Kotlin

class InstallationReceiver(
    a: ((percentage: Int) -> Unit)?
) 

Java

new InstallationReceiver(percentage -> {
    String text = "Installing app" + percentage;
    return Unit.INSTANCE;
});

Also, you're passing true and null where the constructor expects a lambda ( (isUpdated : Boolean) -> Unit ) and a non-nullable String .
You can get away with compiling while passing a null string (you shouldn't since the app will crash at runtime), but for sure you need to pass a lambda instead of a boolean.
Something similar to the example above:

isUpdated -> {
    // your code
    return Unit.INSTANCE;
}