Android: CardView foreground using databinding

Question

I'm trying to fill my RecyclerView with CardViews, the CardViews use Android databinding to set Attributes like Texts in TextViews. On Items that aren't finished jet I want to add a greyish overlay. But unfortunately the foreground android:foreground="@{viewModel.getState != State.FINISHED? @color/gray_transparent54 : null}"> is not applied. On the other hand, if I force the foreground color android:foreground="@grey_transparent54">, it works it is.

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">
    <data class="ListItemBinder">
        <import type="myProject.State"/>
        <import type="android.view.View"/>
        <variable
            name="viewModel"
            type="myProject.ListItemViewModel"/>
    </data>

    <android.support.v7.widget.CardView
        xmlns:card_view="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="80dp"
        card_view:cardCornerRadius="4dp"
        android:foreground="@{viewModel.getState != State.FINISHED? @color/gray_transparent54 : null}">
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@{viewModel.getName}"
                tools:text="Name"
                android:textColor="@color/color_text_primary"
                android:textSize="24sp"/>
    </android.support.v7.widget.CardView>
</layout>

Thanks in advance.

Answer 1

Unless you've implemented getters like getGetState() and getGetName() I think you're accessing your viewModel fields incorrectly. Although you didn't post your ListItemViewModel I suspect you need something closer to this:

<android.support.v7.widget.CardView
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="80dp"
    card_view:cardCornerRadius="4dp"
    android:foreground="@{viewModel.state != State.FINISHED? @color/gray_transparent54 : null}">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{viewModel.name}"
            tools:text="Name"
            android:textColor="@color/color_text_primary"
            android:textSize="24sp"/>
</android.support.v7.widget.CardView>

Data binding automatically looks for a method in your ListItemViewModel class named "getName()" when you access @{viewModel.name}, "getState()" when you access @{viewModel.state} etc.

Note: although UI logic is generally ok, be wary of putting business logic in your XML, as it can limit your flexibility and make testing/debugging more difficult.

Know also that you cannot mix types when using the ternary (?:) operator, so something like choosing between a color int and a drawable will not work. However, you can easily work around this by using custom BindingAdapter methods, e.g. make a binding adapter that takes your ListItemViewModel as a parameter, and put all your logic for what type of value to set within the method itself.