Two-way binding cannot resolve a setter for java.lang.String property

Question

I am playing with the two-way binding of the data binding API which was introduced in Android Studio 2.1 AFIK.

I get this interesting error:

Error:Execution failed for task ':app:compileDebugJavaWithJavac'.
> java.lang.RuntimeException: Found data binding errors.
****/ data binding error ****msg:The expression address.street cannot cannot be inverted: Two-way binding cannot resolve a setter for java.lang.String property 'street'
file:/path/to/layout.xml
loc:34:37 - 34:50 ****\ data binding error ****

When I try to google that error I just find a 4 day old Japanese Twitter posting from a guy who is crying about it...

<EditText
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="@string/edit_hint_zip"
    android:text="@={address.zip}"
    tools:text="12345"/>

That address.zip is a String. I am guessing that the problem here is CharSequence vs. String as the return value of EditText.getText().

My idea was to defining it however this does not work for me:

@NonNull
@InverseBindingAdapter(attribute = "text")
public static String getText(EditText edit) {
    return edit.getText().toString();
}

What did I miss?

Unbound

Answer 1

This bug is ugly as hell and properly a bug in the data binding API. The solution is to generate a setter and a getter. I came up fast with the idea to create a setter, but not to create a getter.

Here is now my simplified model:

public class Address {
    public String street;

    public void setStreet(String street) {
        this.street = street;
    }

    public String getStreet() {
        return street;
    }
}

As you may note the getter and setter are useless, but required for two way binding.

If you think that this is a bug of the API please star my bug report: Two-way binding required setters AND ALSO getters

Unbound

It also works at kotlin for booleans like checkbox checked field – Matrimony

Answer 2

If you are working with kotlin , make sure data class field used for two way binding is declared as var. If it is val unable to support two way binding

Retarder

This worked for me, but cold you give additional information why data binding does not work on val properties – Titi

In Kotlin Val means static. Var means non-static. In databinding, the variable values may be changed so must declare as var. – Retarder

In Kotlin val doesn't mean static it means final. I think speaking from a two way binding perspective, it does make sense to have your class properties declared as var because, you do want their properties to change. – Punak

Answer 3

According to databinding offical repo https://android.googlesource.com/platform/frameworks/data-binding/ commit message, this bug has been fixed at Android Studio 2.2 preview 3.

Prittleprattle

Can you link the commit you are talking about? I see there just one commit which was pushed 8 weeks ago, which seems not to been related. – Unbound

Do you mean the commit 0137f2? – Unbound

Yes, and I also tested on different versions of Android Studio. – Prittleprattle