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android databinding using "&&" logical operator

Posted by: admin March 11, 2020 Leave a comment

Questions:

I am trying to use the and “&&” operator in xml using Android databinding,

android:visibility="@{(bean.currentSpaceId == bean.selectedSpaceId **&&** bean.currentSpaceId > 0)? View.VISIBLE: View.GONE}"

but I got the compilation error:

Error:Execution failed for task ‘:app:dataBindingProcessLayoutsDevDebug’.
org.xml.sax.SAXParseException; systemId: file:/Users/path/app/build/intermediates/res/merged/dev/debug/layout/fragment_space.xml; lineNumber: 106; columnNumber: 89; The entity name must immediately follow the ‘&’ in the entity reference.

and red highlight error in android studio “unescaped & or non terminated character”.

So how should I fix this?

Edit:
found the answer, these character needs to be escaped:

'&' --> '&'

'<' --> '&lt;'

'>' --> '&gt;'
How to&Answers:

&& should be rendered as &amp;&amp;.

The official data binding guide has examples of comparison operators where these XML entities are used, for example

android:visibility="@{age &lt; 13 ? View.GONE : View.VISIBLE}"

Edit

The example expressions I mentioned in the answer disappeared from the English version of the docs since this answer was written. They do survive in some outdated non-English versions of the docs such as the Spanish version.

Either way, the original answer is still valid, because the use of XML entities in XML is standard in XML and has nothing to do with Android itself.

Answer:

List of HTML entities

You can not use & or some other HTML entity in XML. So you have to use escaping character.

android:text="@{(1==1 &amp;&amp; 2>0) ? `true` : `false`}"

HTML Character entities often used in Android:

+--------+----------------------------+--+--+--+
| Symbol | Equivalent HTML Entity     |  |  |  |
+--------+----------------------------+--+--+--+
| >      | &gt;                       |  |  |  |
+--------+----------------------------+--+--+--+
| <      | &lt;                       |  |  |  |
+--------+----------------------------+--+--+--+
| "      | &quot;, &ldquo; or &rdquo; |  |  |  |
+--------+----------------------------+--+--+--+
| '      | &apos;, &lsquo; or &rsquo; |  |  |  |
+--------+----------------------------+--+--+--+
| }      | }                     |  |  |  |
+--------+----------------------------+--+--+--+
| &      | &amp;                      |  |  |  |
+--------+----------------------------+--+--+--+
| space  |                       |  |  |  |
+--------+----------------------------+--+--+--+

Here is a complete list of HTML entities.

Answer:

Escaping && in the layout mark-up is a very poor solution. It is better to create a method on the (view)model object:

android:visibility="@{user.adult ? View.VISIBLE : View.GONE}"

public boolean isAdult() {
    return age >= 18;
}

Answer:

The best solution that I could come up with for this problem was introducing a new Bindable method.

Before:

item_recyclerview.xml:

<EditText
...
android:enabled="@{myViewModel.myDataModelClass.lastAddedItem &amp;&amp; !myViewModel.myDataModelClass.editTextDisabled}"
/>

MyDataModelClass: (which is being held in my viewmodel)

...
private boolean lastAddedItem;
private boolean editTextDisabled;
...
@Bindable
public boolean isLastAddedItem() {
    return lastAddedItem;
}
public void setLastAddedItem(boolean lastAddedItem) {
    this.lastAddeditem = lastAddedItem;
    notifyPropertyChanged(BR.lastAddedItem);
}
@Bindable
public boolean isEditTextDisabled() {
    return editTextDisabled;
}
public void setEditTextDisabled(boolean editTextDisabled) {
    this.editTextDisabled = editTextDisabled;
    notifyPropertyChanged(BR.editTextDisabled);
}

After:

item_recyclerview.xml:

<EditText
...
android:enabled="@{myViewModel.myDataModelClass.enableEditing}"
/>

MyDataModelClass: (which is being held in my viewmodel)

...
private boolean lastAddedItem;
private boolean editTextDisabled;
...
@Bindable
public boolean isLastAddedItem() {
    return lastAddedItem;
}
public void setLastAddedItem(boolean lastAddedItem) {
    this.lastAddeditem = lastAddedItem;
    notifyPropertyChanged(BR.lastAddedItem);
    notifyPropertyChanged(BR.isEnableEditing);
}
@Bindable
public boolean isEditTextDisabled() {
    return editTextDisabled;
}
public void setEditTextDisabled(boolean editTextDisabled) {
    this.editTextDisabled = editTextDisabled;
    notifyPropertyChanged(BR.editTextDisabled);
    notifyPropertyChanged(BR.isEnableEditing);
}
@Bindable
public boolean isEnableEditing() {
    return isLastAddedItem() && !isEditTextDisabled();
}