c# - IF 语句检查控件是否有标记值

Question

我正在尝试遍历一些控件，然后根据控件的位置、宽度和高度制作一个矩形并将其添加到列表中。

C#

List<Rectangle> MaskBlocks = new List<Rectangle>();
foreach (StackPanel gr in FindVisualChildren<StackPanel>(Container))
  if (gr.Tag.ToString() == "Blur")
  {
      System.Windows.Point tmp = gr.TransformToAncestor(this).Transform(new System.Windows.Point(0, 0));
      MaskBlocks.Add(new System.Drawing.Rectangle(new System.Drawing.Point((int)tmp.X,(int)tmp.Y), new System.Drawing.Size((int)gr.ActualWidth, (int)gr.ActualHeight)));
  }

当我运行代码时，IF 语句中出现错误:

An unhandled exception of type 'System.NullReferenceException' occurred in BlurEffectTest.exe

Additional information: Object reference not set to an instance of an object.

有人可以阐明这个问题以便我解决吗？

Answer 1

错误说你的 gr.Tag 是空的，所以它失败了。先检查是否为null

List<Rectangle> MaskBlocks = new List<Rectangle>();
foreach (StackPanel gr in FindVisualChildren<StackPanel>(Container))
if (gr.Tag!= null && gr.Tag.ToString() == "Blur")
{
    System.Windows.Point tmp = gr.TransformToAncestor(this).Transform(new System.Windows.Point(0, 0));
    MaskBlocks.Add(new System.Drawing.Rectangle(new System.Drawing.Point((int)tmp.X,(int)tmp.Y), new System.Drawing.Size((int)gr.ActualWidth, (int)gr.ActualHeight)));
}