c# - 为什么事件指示器不显示？

Question

这是我的 XAML 代码，我试图将一个 ActivityIndi​​cator 放在其他 View 之上，但它根本没有显示，为什么？

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" BackgroundImage="background_nonedit.png" Title="Citizen Reporter" x:Class="BBSTV.CitizenReporter">
    <ScrollView>
        <RelativeLayout VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand">
            <StackLayout VerticalOptions="Center" HorizontalOptions="Fill" Padding="10" RelativeLayout.XConstraint="{ConstraintExpression Type=Constant, Constant=0}" RelativeLayout.YConstraint="{ConstraintExpression Type=Constant, Constant=0}">
                <Grid x:Name="SegmentGrid" RowSpacing="10" ColumnSpacing="10">
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="*" />
                        <ColumnDefinition Width="*" />
                    </Grid.ColumnDefinitions>
                </Grid>
                <Image x:Name="citizenImage" WidthRequest="400" HeightRequest="220" />
                <Label VerticalOptions="Center" HorizontalOptions="Center" Margin="8" x:Name="attachment_label" />
                <Entry Placeholder="News Title" Margin="8" VerticalOptions="Center" HeightRequest="40" />
                <Entry Placeholder="News Details" Margin="8" VerticalOptions="Center" HeightRequest="90" />
                <Button Text="CHOOSE PHOTO" Margin="8" Clicked="onChoosePhoto" TextColor="White" BackgroundColor="#4D7EE1" />
                <Button Text="TAKE  PHOTO" Margin="8" Clicked="onTakePhoto" TextColor="White" BackgroundColor="#4D7EE1" />
                <Button Text="CHOOSE VIDEO" Margin="8" Clicked="onChooseVideo" TextColor="White" BackgroundColor="#4D7EE1" />
                <Button Text="TAKE VIDEO" Margin="8" Clicked="onTakeVideo" TextColor="White" BackgroundColor="#4D7EE1" />
                <Button Text="UPLOAD REPORT" Margin="9" Clicked="UploadFile_Clicked" TextColor="White" BackgroundColor="#F399FC  " />
            </StackLayout>

            <ActivityIndicator x:Name="activity_i_citizenReport" Color="Black" 
                VerticalOptions="CenterAndExpand" HorizontalOptions="CenterAndExpand" 
                 />
        </RelativeLayout>
    </ScrollView>
</ContentPage>

Answer 1

ActivityIndicator有一些属性。

可见

正在运行

启用

尝试将这些属性设置为“true”