How do focus and unFocus in many entries - xamarin.forms

Question

i have this view
<Entry Placeholder="Name" WidthRequest="200" Text="">
<Entry.Triggers>
<EventTrigger Event="Focused">
<local:SizeText />
</EventTrigger>
</Entry.Triggers>
</Entry>
i want that when the Entry have one or more characters it be paint with other color and have the focus but when have not the focus it be paint with other color
protected override void Invoke(Entry entry)
{
if (entry.IsFocused) {
if (entry.Text.Length == 0)
{
entry.BackgroundColor = Color.Yellow;
}
}
else{
Console.WriteLine("CCCHCH");
entry.BackgroundColor = Color.White;
}
}
my don't work for me, how i can enhacement?

Answer 1

Try this one:
<Entry Placeholder="enter name">
<Entry.Triggers>
<Trigger TargetType="Entry" Property="IsFocused" Value="True">
<Setter Property="BackgroundColor" Value="Yellow" />
</Trigger>
<Trigger TargetType="Entry" Property="IsFocused" Value="False">
<Setter Property="BackgroundColor" Value="Red" />
</Trigger>
</Entry.Triggers>
</Entry>

Answer 2

I'm not sure which solution you want ,there are two ways to Change BackgroundColor of Entry .
One is Designed method ,using Triggers can easy to do that , have a look at this official document .
A simple trigger can be expressed purely in XAML, adding a Trigger element to a control's triggers collection. This example shows a trigger that changes an Entry background color when it receives focus and unfocus:
<Entry Placeholder="Trigger effect">
<Entry.Triggers>
<Trigger TargetType="Entry"
Property="IsFocused"
Value="True">
<Setter Property="BackgroundColor"
Value="Yellow" />
<!-- multiple Setters elements are allowed -->
</Trigger>
<Trigger TargetType="Entry"
Property="IsFocused"
Value="False">
<Setter Property="BackgroundColor"
Value="Gray" />
</Trigger>
</Entry.Triggers>
</Entry>
Another one is Runtime method , using Focused and Unfocused to implement it .
The VisualElement class, from which Entry inherits, also has Focused and Unfocused events.
<Entry Placeholder="Focused / Unfocused method" Focused="Entry_Focused" Unfocused="myentry_Unfocused"/>
Need dealing with events in ContentPage :
private void Entry_Focused(object sender, FocusEventArgs e)
{
var entry = sender as Xamarin.Forms.Entry;
entry.BackgroundColor = Color.Red;
}
private void myentry_Unfocused(object sender, FocusEventArgs e)
{
var entry = sender as Xamarin.Forms.Entry;
entry.BackgroundColor = Color.Gray;
}
I will show their effects , there will be some differents between them before first tapping them. As follow :
Note : It depends on your scene to choose which one .