Fabian Fabian - 5 months ago 11
Android Question

Android Data Binding - Reference to view

I use in my new app the data binding library of android.
Currently I try to pass a reference of another view to a method.

I have an ImageButton with an onClick-Listener. In this onClick listener I want to pass a reference of the root view to the method.

<RelativLayout
android:id="@+id/root_element"
android:layout_width="match_parent"
android:layout_height="match_parent">

<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentStart="true"
android:contentDescription="@string/close_dialog"
android:src="@drawable/ic_close_212121_24dp"
android:background="@android:color/transparent"
android:onClick="@{() -> Helper.doSth(root_element)}"/>
</RelativLayout>


This source code provided above is only an example and not the complete.
There are more children and also the image button is not a direct child of the root element. But I think the meaning is clear.

I already tried to pass a reference by specifing the id of the root view (see above). But this doesn't work. If I try to compile this, I get the error, that the type of root_element is not specified.

I also tried to import the generated binding class and access the root element by the public field in it. Also this method doesn't work, since the binding class has to be generated first.

So is there any way to pass a reference of a view to a method?
I know that I could pass the id of the root view with @id/root_element, but I don't want that, since I have to find a way to get a reference to this view only with the given id.

Answer

The difference between what you have and what you should do is, don't pass the id root_element. Rather, pass through the view as another variable into the layout file.

In my case, I had a switch in my layout, that I wanted to pass as a parameter to a method in my lambda. My code is like this:

    MyLayoutBinding binding = DataBindingUtil.inflate(inflater, R.layout.my_layout, parent, true);
    binding.setDataUpdater(mDataUpdater);
    binding.setTheSwitch(binding.switchFavorite);

Then my layout is like this:

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <data>
        <variable name="dataUpdater" type="..."/>
        <variable name="theSwitch" type="android.widget.Switch"/>
        <import type="android.view.View"/>
    </data>
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="@{()->dataUpdater.doSomething(theSwitch)}">
        <Switch
            style="@style/Switch"
            android:id="@+id/switch_favorite"
            ... />
.../>

So as you can see with this, in my code, I get the reference to my switch and pass it in as a variable in the binding. Then in my layout I then have access to it, to pass it through in my lambda.

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