在设置一些控件的事件处理Lambda表达式不工作 [英] Lambda expression not working in setting the event-handler of some controls
问题描述
我创建控件数组,并将它们添加到窗体,并设置自己的事件接收点击的按钮使用lambda表达式的指数函数( b.Click + =(发件人,E)=> MyClick认证(I);
)
$ b $无论你点击第b
但问题是......,您会收到索引100中,而不是按钮的实折射率!什么是这里的问题。
命名空间testArrayOfControls
{
公共部分Form1类:表
{
键[]按钮;
公共Form1中()
{
的InitializeComponent();
键=新的Button [100];
的for(int i = 0; I< 100;我++)
{
按钮[i] =新的Button();
按钮[I] .SetBounds(ⅰ%10 * 50,I / 10 * 50,50,50);
按钮[i]。点击+ =(发件人,E)=>了MyClick(ⅰ);
this.Controls.Add(按钮[I]);
}
}
私人无效了MyClick(int i)以
{
MessageBox.Show(i.ToString());
}
}
}
的问题是,您在循环变量创建封我
。你需要将它传递给事件处理程序之前进行局部的它(为
循环内)的副本。
的for(int i = 0; I< 100;我++)
{
变种指数= I; //你需要这样做
按钮[i] =新的Button();
按钮[I] .SetBounds(ⅰ%10 * 50,I / 10 * 50,50,50);
按钮[i]。点击+ =(发件人,E)=> MyClick认证(指数); //这解决了问题
this.Controls.Add(按钮[I]);
}
说明
您正在定义这样的功能:
(发件人,E)=> MyClick认证(I)
这功能(这将在未来的某个时刻,当按钮运行点击)包括对 I
的参考。 ,其工作原理是,它会在的时候发生的点击,而不是当时的函数定义的使用 I
的值
到那个时候, I
将成为100。
解决方案的工作,因为它使函数取到变量的引用首页
而不是 I
。 首页
从不同我
在 I
是一个变量,其值的变化,而首页
是我们使用100种不同的变量(每个循环迭代)的名称,,它的值保持不变的
I'm creating an array of controls and adding them to the form, and setting their events to a function that receives the index of the clicked button using a lambda expression (b.Click += (sender, e) => myClick(i);
).
But the problem is... Whichever you click on, you receive the index 100, not the real index of the button! What is the problem here?
namespace testArrayOfControls
{
public partial class Form1 : Form
{
Button[] buttons;
public Form1()
{
InitializeComponent();
buttons = new Button[100];
for (int i = 0; i < 100; i++)
{
buttons[i] = new Button();
buttons[i].SetBounds(i % 10 * 50, i / 10 * 50, 50, 50);
buttons[i].Click += (sender, e) => myClick(i);
this.Controls.Add(buttons[i]);
}
}
private void myClick(int i)
{
MessageBox.Show(i.ToString());
}
}
}
The problem is that you create closure over the loop variable i
. You need to make a local (inside the for
loop) copy of it before passing it to the event handler.
for (int i = 0; i < 100; i++)
{
var index = i; // YOU NEED TO DO THIS
buttons[i] = new Button();
buttons[i].SetBounds(i % 10 * 50, i / 10 * 50, 50, 50);
buttons[i].Click += (sender, e) => myClick(index); // THIS SOLVES THE PROBLEM
this.Controls.Add(buttons[i]);
}
Explanation
You are defining a function like this:
(sender, e) => myClick(i)
This function (which will run at some point in the future, when the button is clicked) includes a reference to i
. The way, this works is that it will use the value of i
at the time when the click occurs, not at the time the function is defined.
By that time, clearly the value of i
will have become 100.
The solution works because it makes the function take a reference to the variable index
instead of i
. index
differs from i
in that i
is one variable whose value changes, while index
is a name we use for 100 different variables (one for each loop iteration), the value of which remains constant.
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