具有主题属性的数据绑定

Question

I am trying out the new Android Databinding Library and I wanted to set the background color of ToolBar using a binding. By default the color should be colorPrimary (from the theme).

Before I was using DataBinding, my toolBar looked like

 <android.support.v7.widget.Toolbar
        android:id="@+id/mainToolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        />

After adding a binding, I wanted to set its background to colorPrimary if no color is bound - I'm using ternary operator for this (as mentioned in the guide) - but it causes an error, as theme attributes also have a "?" operator before their names. The compiler thinks I'm starting a new ternary operation.

<data>
    <variable name="toolBarBackgroundColor" type="int"/>
</data>
...
<android.support.v7.widget.Toolbar
        android:id="@+id/mainToolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="@{toolBarBackgroundColor!=0? toolBarBackgroundColor: ?attr/colorPrimary }"
        />

So is there a way I can access theme attributes inside a binding operation? Thanks!

Edit

I know I can get the colorPrimary attribute programmatically and bind it through java code. But I'm just wondering if there's an Xml-based solution for this or not.

Answer 1

The answer is a bit late, but maybe it helps someone.

For accessing theme attributes in data binding, you can use this:

(imagine that clickable is Boolean variable)

android:background="@{clickable ? android.R.attr.selectableItemBackground : android.R.color.transparent}"

No additional binding adapters or another things needed.

Answer 2

Finding a way using data-binding? Here is what I have done with test. First, create a custom binding adapter method:

@BindingAdapter({"app:customPrimaryBackground"})
public static void setCustomPrimaryBackground(View v, int resId) {
    TypedValue typedValue = new TypedValue();
    Context context = v.getContext();
    if (resId == 0) {
        context.getTheme().resolveAttribute(R.attr.colorPrimary, typedValue, true);
        v.setBackgroundResource(typedValue.resourceId);
    } else {
        // Check the given resource ID is a color or drawable
        context.getResources().getValue(resId, typedValue, true);
        Drawable drawable;
        if (typedValue.type >= TypedValue.TYPE_FIRST_COLOR_INT && typedValue.type <= TypedValue.TYPE_LAST_COLOR_INT) {
            // It's a color
            drawable = new ColorDrawable(typedValue.data);
        } else {
            drawable = ContextCompat.getDrawable(context, resId);
        }

        v.setBackground(drawable);
    }
}

Second, your binding xml layout:

<data>
    <variable name="toolBarBackgroundColor" type="int"/>
</data>
...
<android.support.v7.widget.Toolbar
        android:id="@+id/mainToolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        app:customPrimaryBackground="@{toolBarBackgroundColor}"
/>

Answer 3

如果问题对某人来说仍然是实际的，这是如何使用自定义和 android 属性app:textColorAttr="@{error ? com.example.R.attr.textColorError : android.R.attr.textColor}" ，其中textColorAttr 使用BindingAdapter实现， error是Boolean ， com.example是你的包名

Answer 4

I found another solution without custom attributes and binding adapters. The idea is to place an invisible View with android:background and android:foreground attributes in XML markup and use these attributes in a binding expression.

<data>
    <variable name="toolBarBackgroundColor" type="int"/>
</data>

...

<android.support.v7.widget.Toolbar
    android:id="@+id/mainToolbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:background="@{toolBarBackgroundColor != 0 ? helperView.getBackground() : helperView.getForeground() }"
    />

<View
    android:id="@+id/helperView"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:background="@{toolBarBackgroundColor}"
    android:foreground="?attr/colorPrimary"
    android:visibility="gone"
    />