Question

这是我的XAML代码我试图将ActivityIndicator放在其他视图之上，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

相对布局会将控件放在与其兄弟姐妹相关的位置，因此它可能会将堆栈布局渲染到指标的顶部，或者只是在其下方并且看不见。记录在案here。

我只是将它放在滚动视图的外部，因为滚动视图的内容大小可变，因此有时可能有点难以计算死点，而如果您直接将活动控件分配给内容页面它总是在中心。如果以下方法不起作用，您可能必须使用Z-Index。

<?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">
<ContentPage.Content>

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

    <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>
        </RelativeLayout>
      </ScrollView>
   </ContentPage.Content>
</ContentPage>

Answer 2

ActivityIndicator有一些属性。

ISVISIBLE

IsRunning

的IsEnabled

尝试将这些属性设置为＆＃34; true＆＃34;

Answer 3

我在项目中所做的工作

在Grid我使用ScrollView作为<Grid HorizontalOptions="FillAndExpand"> <ScrollView HorizontalOptions="FillAndExpand">  </ScrollView> <Frame Padding="50,30,50,30" HasShadow="true" BackgroundColor="#80000000" Grid.Row="0" Grid.Column="0" IsVisible="{Binding IsLoading}" VerticalOptions="Center" HorizontalOptions="Center"> <ActivityIndicator Color="White" VerticalOptions="Center" HorizontalOptions="Center" x:Name="actInd" IsRunning="{Binding IsLoading}" IsVisible="{Binding IsLoading}" /> </Frame> </Grid>的父级。

INotifyPropertyChanged

在Page中实施BindingContext = this;。在构造函数中，设置

PropertyChangedEventHandler

之后，使用我们的自定义属性在您的页面中创建private bool isLoading; public bool IsLoading { get { return isLoading; } set { isLoading = value; RaisePropertyChanged("IsLoading"); } } public event PropertyChangedEventHandler PropertyChanged; public void RaisePropertyChanged(string propName) { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(propName)); } }。

IsLoading

现在我们只需更改private void doStuffs() { IsLoading = true; IsBusy = true; //Do any stuffs IsLoading = false; IsBusy = false; }的值即可显示ActivityIndicator。

byte[]

Answer 4

就我所关注的问题而言，所有关于将其置于StackLayout中的讨论都是h ..我的定义是Grid，但根本不显示。当我在Windows 10（UWP）上运行它时，如果仅IsRunning设置为true，则根本不会显示;但如果您将IsEnabled或IsVisible设置为true 与IsRunning结合，则会显示约两秒钟，然后淡出并且永不显示再次。请注意，IsRunning，IsEnabled和IsVisible仅设置一次并且没有时间密集型操作正在运行UI线程。

这绝对是个错误。我会使用动画GIF，直到Xamarin团队得到修复。如果它无法在所有平台上运行，那么它基本上是无用的。

为什么活动指标没有显示？

4 个答案: