Setting OnCheckedChangeListener with a Lambda

Question

I want to use a lambda rather than an anonymous class for OnCheckedChangeListener.

The original code for setting the listener works fine and reads:

mCheckBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
    @Override
    public void onCheckedChanged(CompoundButton buttonView,boolean isChecked) {
        mCrime.setSolved(isChecked);
    }
});

I tried changing it to a lambda by doing:

mCheckBox.setOnCheckedChangeListener(l -> mCrime.setSolved(isChecked));

but I receive an error from Android Studio saying: cannot resolve symbol is checked.

I had thought a lambda would resolve isChecked implicitly even though the onCheckChanged takes two arguments. What is wrong with my understanding?

Answer 1

Your syntax is wrong. What you have shouldn't even compile. Use this:

mCheckBox.setOnCheckedChangeListener((view, isChecked) -> mCrime.setSolved(isChecked));

The stuff before the -> doesn't represent the listener, but rather the arguments that are passed in that listener, in this case a View and a boolean.

Answer 2

isChecked is just a parameter name it is not there when you are using lambdas how ever here is the correct lambda with the parameter names for your onCheckChangeListener

mCheckBox.setOnCheckedChangeListener((CompoundButton.OnCheckedChangeListener) (buttonView, isChecked) -> mCrime.setSolved(isChecked));