使用选择器填充图像源

Question

我正在尝试根据此 https://learn.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/dependency-service/photo-picker 从选择器填充图像

选择器工作正常，流已满。 但是我没有在屏幕上看到图片。

public Command SelectPictureCommand { get; }
public ImageSource ItemPic { get; set; }
SelectPictureCommand = new Command(execute: async () =>
{
if (IsBusy)
{
return;
}
IsBusy = true;
try
{
Stream stream = await DependencyService.Get<IPhotoPickerService>().GetImageStreamAsync();
if (stream != null)
{
ItemPic = ImageSource.FromStream(() => stream);
}
}
catch (Exception ex)
{
Debug.WriteLine(ex);
}
finally
{
IsBusy = false;
}
});

XAML

<StackLayout Orientation="Vertical" HorizontalOptions="End">
<Button Text="Select Picture" Command="{Binding SelectPictureCommand}"/>
<Image Source="{Binding ItemPic}" WidthRequest="300" HeightRequest="300"/>
</StackLayout>

Answer 1

您应该在 ViewModel 或模型中实现 INotifyPropertyChanged 接口：

ViewModels通常实现INotifyPropertyChanged接口， 这意味着该类在任何时候都会触发 PropertyChanged 事件 其属性更改。Xamarin.Forms 中的数据绑定机制 将处理程序附加到此 PropertyChanged 事件，以便可以通知它 当属性发生更改并使用新的 价值。

public class myViewModel : INotifyPropertyChanged {
public event PropertyChangedEventHandler PropertyChanged;
public Command SelectPictureCommand { get; }
public ImageSource itemPic { get; set; }

public ImageSource ItemPic
{
set
{
if (itemPic != value)
{
itemPic = value;
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("ItemPic"));
}
}
}
get
{
return itemPic;
}
}
public myViewModel() {
SelectPictureCommand = new Command(execute: async () =>
{
//if (IsBusy)
//{
//    return;
//}
//IsBusy = true;
try
{
Stream stream = await DependencyService.Get<IPhotoPickerService>().GetImageStreamAsync();
if (stream != null)
{
ItemPic = ImageSource.FromStream(() => stream);
}
}
catch (Exception ex)
{
Debug.WriteLine(ex);
}
finally
{
//IsBusy = false;
}
});
}
}

我在这里上传了一个样本，你可以检查。如果您有任何问题，请随时问我。

Answer 2

您可以使用跨媒体插件，例如：

await CrossMedia.Current.Initialize();
var file = await CrossMedia.Current.PickPhotoAsync();
var filestream = file.GetStream();
byte[] buff = ConverteStreamToByteArray(filestream);
image.Source = ImageSource.FromStream(buff);
filestream.Dispose();