wpf imagesource=null 同时清空内存

确保imagesource只有image控件引用的情况下，这么赋值：

BitmapImage image = new BitmapImage();
image.BeginInit();
image.CacheOption = BitmapCacheOption.OnLoad;
image.UriSource = new Uri(list[current], UriKind.RelativeOrAbsolute);
image.EndInit();

Image imageControl = new Image();
imageControl.Source = image;

测试代码：
///

/// MainWindow.xaml 的交互逻辑
///

public partial class MainWindow : Window
{
List list = new List();
public MainWindow()
{
InitializeComponent();
string dir = @"C:\Users\Sam\Pictures\大图";
for (int i = 0; i < 6; i++)
{
list.Add($"{dir}{i}.png");
}
}

int current = 0;
int max = 5;

//HttpClient httpClient = new HttpClient();
private /async/ void Button_Click(object sender, RoutedEventArgs e)
{

//不清空图片控件，清除每个图片控件的source
foreach (var item in container.Children)
{
if (item is Image)
{
Image img = (Image)item;
img.Source = null;
}
}

////清空图片控件--ok，可以清空内存
//var listx = new List();
//for (int i = 0; i < container.Children.Count; i++)
//{
// if (container.Children[i] is Image)
// {
// Image img = (Image)container.Children[i];
// listx.Add(img);
// }
//}
//foreach (var item in listx)
//{
// container.Children.Remove(item);
//}

GC.Collect();

//Image image = new Image();
//image.Source = new BitmapImage(new Uri(list[current], UriKind.RelativeOrAbsolute));

BitmapImage image = new BitmapImage();
image.BeginInit();
image.CacheOption = BitmapCacheOption.OnLoad;
image.UriSource = new Uri(list[current], UriKind.RelativeOrAbsolute);
image.EndInit();

Image imageControl = new Image();
imageControl.Source = image;

container.Children.Add(imageControl);

current++;
if (current > max)
{
current = 0;
}

}

}