更改矩形列表中矩形的x值 [英] Change x value of rectangle in rectangle list

问题描述

我在表单应用程序中创建了一个矩形列表，需要在此列表中创建一个矩形移动。这是我的代码：

 List< Rectangle> squares = new List< Rectangle>（）; 
 
 //假设我做了一个名为r 
 squares.Add（r）的任意矩形; 
 
 //这是我需要做的事情
 for（int i = 0; i< squares.Count; i ++）{
 
 //问题在这里
 square [i] .X + = 5; 
 
} 

我收到错误消息，说它无法修改返回值，因为它不是变量。我明白了，但我需要知道是否有办法绕过这个或其他方式来做到这一点。请帮忙。谢谢。

解决方案

可变值类型（struct）的字段，如Rectangle，如果它们在通用列表中，则不能直接赋值给它们。



虽然你可以使用'Offset方法没有错误，如果你使用一般的矩形列表，访问矩形将返回它的副本，'偏移运算符将处理该副本，使列表中的矩形保持不变。



解决方案是使用数组结构来保存矩形：

  private  Rectangle [] rList =  new 矩形[ 25 ]; 
 
  private   void  MakeRects（）
 {
  for （ int  i =  0 ; i <   5 ; i ++）
 {
  for （ int  j =  0 ; j <   5 ; j ++）
 {
 Rectangle r =  new 矩形（i * 50，j * 50， 100 ， 100 ）; 
 rList [（i * 5）+ j] = r; 
} 
} 
 
 rList [ 2 ]。偏移量（ 1000 ， 1000 ）; 
 rList [ 3 ]。Y + =  4000 ; 
  //  在这里设置一个断点：检查rList [2]，rList的X和Y值[ 3]  
} 

如果你必须使用一个矩形列表，你别无选择，只能创建一个新的矩形，然后插入它代替原始的矩形。 / blockquote>

等我发现了，我只需要创建一个新的矩形，更改值，然后用新的矩形替换原始的矩形。

I made a rectangle list in a forms application and need to make a rectangle in this list move. Here is my code:

List<Rectangle> squares = new List<Rectangle>();

// Assume I have made some arbitrary rectangle named r
squares.Add(r);

// Here is what I need to do
for (int i = 0; i < squares.Count; i++) {

    // Problem Here
    squares[i].X += 5;

}

I get an error saying that it cannot modify the return value because it's not a variable. I get it but I need to know if there is a way to get around this or another way to do this. Please help. Thanks.

解决方案

Fields of a mutable value-type (struct), like a Rectangle, are, by design, not assignable to directly if they are in a Generic List.

While you can use the 'Offset method without error, if you use a generic List of Rectangles, accessing the Rectangle will return a copy of it, and the 'Offset operator will work on that copy, leaving the Rectangle in the List unchanged.

A solution is to use an Array structure to hold your Rectangles:

private Rectangle[] rList = new Rectangle[25];

private void MakeRects()
{
    for (int i = 0; i < 5; i++)
    {
        for (int j = 0; j < 5; j++)
        {
            Rectangle r = new Rectangle(i*50, j*50, 100, 100);
            rList[(i*5) + j] = r;
        }
    }

    rList[2].Offset(1000, 1000);
    rList[3].Y += 4000;
    // put a break-point here: examine X and Y values of rList[2], rList[3]
}

If you have to use a List of Rectangles, you have no choice but to create a new Rectangle and then insert it in place of the original one.

Wait I figured it out, I just needed to create a new rectangle, change the values, then replace the original rectangle with the new one.

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