C# 无法将 [] 索引应用于“对象”类型的表达式
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Cannot apply indexing with [] to an expression of type `object'
提问by JamesB
Here is my code: An ArrayList of ArrayList that returns a float:
这是我的代码：返回浮点数的 ArrayList 的 ArrayList：
public ArrayList paredes=new ArrayList();
public void Start()
{
paredes[0] = RetornaEmArrayList(279,275,0,0,90);
paredes[1] = RetornaEmArrayList(62,275,0,0,0);
paredes[2] = RetornaEmArrayList(62,275,62,0,90);
paredes[3] = RetornaEmArrayList(217,275,62,-62,0);
paredes[4] = RetornaEmArrayList(62,275,279,0,90);
paredes[5] = RetornaEmArrayList(41,275,279,0,0);
paredes[6] = RetornaEmArrayList(279,275,320,0,9);
paredes[7] = RetornaEmArrayList(320,275,0,-279,0);
for (int i = 0; i < paredes.Length; i++) {
float a = (float)paredes[i][0];
float b = (float)paredes[i][1];
float c = (float)paredes[i][2];
float d = (float)paredes[i][3];
float e = (float)paredes[i][4];
}
}
ArrayList RetornaEmArrayList(float a,float b,float c, float d, float e)
{
ArrayList arrayList = new ArrayList();
arrayList.Add(a);
arrayList.Add(b);
arrayList.Add(c);
arrayList.Add(d);
arrayList.Add(e);
return arrayList;
}
It gives me the following error:
它给了我以下错误：
error CS0021: Cannot apply indexing with [] to an expression of type `object'
错误 CS0021：无法将 [] 索引应用于“对象”类型的表达式
I already did the casting, what is wrong? :(
我已经进行了选角，有什么问题吗？:(
采纳答案by Lee
The problem is that paredes[i]returns an objectwhich is the return type of the ArrayListindexer. You need to cast this to an ArrayListto be able to access it:
问题在于paredes[i]返回的object是ArrayList索引器的返回类型。您需要将此转换为 anArrayList才能访问它：
float a= (float)((ArrayList)paredes[i])[0];
A better solution though is to use generics and populate a List<float>instead:
更好的解决方案是使用泛型并填充 a List<float>：
List<float> RetornaEmList(float a,float b,float c, float d, float e)
{
return new List<float> { a, b, c, d, e };
}
then paredesis a List<List<float>>and your accessor can be changed to:
然后paredes是 aList<List<float>>并且您的访问器可以更改为：
float a = paredes[i][0];
回答by CSharper
Where are you doing the casting?
你在哪里选角？
I would say it must be (did not try with a compiler):
我会说它必须是（没有尝试使用编译器）：
for (int i = 0; i < paredes.Length; i++)
{
float a=(float)((ArrayList)paredes[i])[0];
...
}
Did you consider using the generic collections instead?
您是否考虑过使用泛型集合？
public List<List<float>> paredes = new List<List<float>>();
回答by Scott Chapman
ArrayListstores objects without limiting what type those objects are. When you access the objects stored in an ArrayList, the compiler doesn't know what type they are, so it just gives you type object.
ArrayList存储对象而不限制这些对象的类型。当您访问存储在 an 中的对象时ArrayList，编译器不知道它们是什么类型，因此它只为您提供 type object。
You're storing an ArrayListof floatin your outer ArrayList. Since you're always storing floats, it would be better to use a List<float>for the inner list, and a List<List<float>>for the outer list. This way you won't have to type cast from object:
您将ArrayListof存储float在您的外部ArrayList. 由于您总是存储浮点数，因此最好将 aList<float>用于内部列表，而 aList<List<float>>用于外部列表。这样你就不必输入 cast from object：
using System.Collections.Generic;
public List<List<float>> paredes = new List<List<float>>();
Start() {
paredes[0]=RetornaEmList(279,275,0,0,90);
paredes[1]=RetornaEmList(62,275,0,0,0);
paredes[2]=RetornaEmList(62,275,62,0,90);
paredes[3]=RetornaEmList(217,275,62,-62,0);
paredes[4]=RetornaEmList(62,275,279,0,90);
paredes[5]=RetornaEmList(41,275,279,0,0);
paredes[6]=RetornaEmList(279,275,320,0,9);
paredes[7]=RetornaEmList(320,275,0,-279,0);
for (int i=0;i<paredes.Length;i++)
{
float a=paredes[i][0];
float b=paredes[i][1];
float c=paredes[i][2];
float d=paredes[i][3];
float e=paredes[i][4];
}
}
List<float> RetornaEmList(float a,float b,float c, float d, float e)
{
return new List<float> { a, b, c, d, e };
}
Since the inner list always has 5 floats, you could also use a float[]instead of a List<float>
由于内部列表总是有 5 个浮点数，您也可以使用 afloat[]而不是 aList<float>
If you just want to make the code work without moving from ArrayListto List, you need an additional cast:
如果您只想使代码工作而不从ArrayListto移动List，则需要额外的演员阵容：
float a = (float)((ArrayList)paredes[i])[0];
But it's a lot cleaner just to use List<float>instead.
但只是使用它更干净List<float>。
回答by Kundan Singh Chouhan
Code should be like this :
代码应该是这样的：
//Adding List
paredes.Add(RetornaEmArrayList(279,275,0,0,90));
paredes.Add(RetornaEmArrayList(62,275,0,0,0));
paredes.Add(RetornaEmArrayList(62,275,62,0,90));
paredes.Add(RetornaEmArrayList(217,275,62,-62,0));
paredes.Add(RetornaEmArrayList(62,275,279,0,90));
paredes.Add(RetornaEmArrayList(41,275,279,0,0));
paredes.Add(RetornaEmArrayList(279,275,320,0,9));
paredes.Add(RetornaEmArrayList(320,275,0,-279,0));
//Traversing List
foreach(ArrayList item in paredes)
{
float a=(float)item[0];
float b=(float)item[1];
float c=(float)item[2];
float d=(float)item[3];
float e=(float)item[4];
}
