R.id.code报Constant expression required

在 Android 中，R.id.code 表示获取布局文件中某个 View 的 id，但是在某些情况下，使用 R.id.code 会出现 "Constant expression required" 的错误提示，这通常是由于以下原因导致的：

1. 在定义数组时使用了变量作为数组长度，而不是使用常量表达式。

2. 在 switch 语句中使用了非常量表达式作为 case 标签。

解决方法：

1. 如果 R.id.code 用于数组长度，应该使用常量表达式作为数组长度。可以使用 const 关键字定义常量，或者使用 #define 宏定义。

2. 如果 R.id.code 用于 switch 语句中的 case 标签，应该使用常量表达式作为 case 标签。如果需要使用非常量表达式，可以考虑使用 if-else 语句替代。

总之，需要避免在需要使用常量表达式的地方使用非常量表达式，以确保程序的正确性和可读性。

相关问题

Android Studio Constant expression required

"Constant expression required" error in Android Studio usually occurs when you try to use a non-constant value in a place where a constant value is required.

To fix this error, you need to make sure that all the values that you use in the code are constants. For example, if you are defining an array size, you need to use a constant value instead of a variable.

Here is an example:

int size = 10;
int[] arr = new int[size]; // This will cause "Constant expression required" error

// To fix this error, you can define the array size as a constant value:
final int SIZE = 10;
int[] arr = new int[SIZE];

By defining the array size as a constant value, you can avoid the "Constant expression required" error in Android Studio.

java switch Constant expression required

In Java, the switch statement requires a constant expression as its argument. A constant expression is an expression whose value can be determined at compile-time and does not change during the execution of the program. It means that the value being tested in the switch statement must be a constant, like a literal value or a final variable.

If you encounter the error message "Constant expression required" in a switch statement, it means that the value you provided is not considered a constant expression. To resolve this issue, you can try using if-else statements instead of a switch statement or ensure that the value being tested meets the criteria of a constant expression.

Here's an example of a switch statement with a constant expression:

final int num = 2;
switch (num) {
    case 1:
        // code for case 1
        break;
    case 2:
        // code for case 2
        break;
    default:
        // code for default case
}

In this example, the variable `num` is declared as `final`, making it a constant. Hence, it can be used in the switch statement.