Data binding: set property if it isn't null
AndroidAndroid DatabindingAndroid Problem Overview
Cannot understand... How to set some property of view only if variable field isn't null?
For example
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">
<data>
<variable
name="item"
type="com.test.app.Item" />
</data>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="60dp"
android:orientation="horizontal">
<ImageView
android:id="@+id/icon"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_centerVertical="true"
android:layout_margin="16dp"
android:src="@{item.getDrawable()}"/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:layout_marginEnd="16dp"
android:layout_marginLeft="72dp"
android:layout_marginRight="16dp"
android:layout_marginStart="72dp"
android:layout_toLeftOf="@id/action"
android:layout_toStartOf="@id/action"
android:orientation="vertical">
<TextView
android:id="@+id/text1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:singleLine="true"
android:textColor="@color/black_87"
android:textSize="16sp"
android:text="@{item.getTitle()}"/>
<TextView
android:id="@+id/text2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:autoLink="web|email"
android:linksClickable="false"
android:singleLine="true"
android:textColor="@color/black_54"
android:textSize="14sp"
android:text="@{item.getSubtitle()}"/>
</LinearLayout>
</RelativeLayout>
</layout>
Some field of Item can be null and I won't call methods of layout views unnecessarily. And I won't get NullPointerException
. How can I set property only if it isn't null?
P.S. Sorry for English.
Android Solutions
Solution 1 - Android
Well data binding avoids NullPointerException in general by checking for it and assigns the default value (null for example) even if item
itself is null in your example.
But a basic example for null checks for the item's properties:
android:text='@{item.title != null ? user.title : ""}'
Or use the "Null Coalescing Operator". The null coalescing operator (??
) chooses the left operand if it is not null or the right if it is null.
android:text='@{item.title ?? ""}'
Note that title
or getTitle
doesn't matter.
Solution 2 - Android
> Data binding does not need to check for null value, it will be handled > by binding class.
If you need to check null for other purpose (like setting default value) then you can use like this.
android:text='@{item.gender != null ? item.gender : @string/male}'
or
android:text='@{item.gender ?? @string/male}'
Both above examples are same. Here @string/male
is default value, when item.gender
is null
.
Solution 3 - Android
I tried something like this.
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<data>
<import type="android.text.TextUtils"/>
<variable
name="mOrder"
type="com.test.app.models.Order" />
</data>
<TextView
android:id="@+id/mLblSource"
android:layout_width="100dp"
android:layout_height="40dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:text='@{TextUtils.isEmpty(mOrder.order_id) ? "- -" : mOrder.order_id}'
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintBottom_toBottomOf="parent" />
</layout>