将对象添加到 NSMutableArray 或将 Float 转换为 NSNumber

Question

显然在向 NSMutableArray 添加元素或将浮点数转换为 NSNumber 时遇到困难。

这是一个有效的 while 循环，它使用简单的 C 数组而不是 NSMutableArray。它是用 printf's 测试的：

    #define MAXSIZE 50

    float xCoordinate [MAXSIZE] = {0.0};
    float yCoordinate [MAXSIZE] = {0.0};

    float x;
    float y;

    // ... some code creating handle from a .txt file

        while ((fscanf(handle, " (%f;%f)", &x, &y)) == 2)
        {
            printf("%f\n",x);
            printf("%f\n",y);

            xCoordinate[n] = x;
            yCoordinate[n] = y;

            printf("Here is value from the array %f\n", xCoordinate[n]);
            printf("Here is value from the array %f\n", yCoordinate[n] );
            n++;
            if ( n >= MAXSIZE)
            {
                break;
            }
        }

我想切换到 NSMutable 数组的原因是因为我想计算 xCoordinate 或 yCoordinate 数组中元素的数量。我认为将函数 count 发送到数组更容易。

这里有一些循环对我不起作用，并且不将 scanf 的值分配给 x 和 y。

使用while循环：

    NSMutableArray *xCoordinate;
    NSMutableArray *yCoordinate;
    float x;
    float y;
    int n =0;

    while ( ( fscanf(handle, " (%f;%f)", &x, &y) ) == 2)
        {    
            // these 2 lines don't work as suppose to. What's wrong?        
            [xCoordinate addObject:[NSNumber numberWithFloat:x]];
            [yCoordinate addObject:[NSNumber numberWithFloat:y]];


            printf("asdf %f\n", [[xCoordinate objectAtIndex:n] floatValue]);
            printf("asdf %f\n", [[yCoordinate objectAtIndex:n] floatValue]);



            n++;
            if ( n >= MAXSIZE)
            {
                break;
            }
        }

使用 for 循环：

    NSMutableArray *xCoordinate;
    NSMutableArray *yCoordinate;
    float x;
    float y;   

    for  (n=0; ((fscanf(handle, " (%f;%f)", &x, &y)) == 2); n++)
        {
            // these 2 lines don't work as suppose to. What's wrong?        
            [xCoordinate addObject:[NSNumber numberWithFloat:x]];
            [yCoordinate addObject:[NSNumber numberWithFloat:y]];


            printf("asdf %f\n", [[xCoordinate objectAtIndex:n] floatValue]);
            printf("asdf %f\n", [[yCoordinate objectAtIndex:n] floatValue]);

            if ( n >= MAXSIZE)
            {
                break;
            }
        }

Answer 1

您永远不会创建数组实例，所以您总是试图将项目添加到空，这在 Objective-C 中是一个静默的空操作。将第一行更改为：

NSMutableArray *xCoordinate = [NSMutableArray array];
NSMutableArray *yCoordinate = [NSMutableArray array];

将对象添加到 NSMutableArray 或将 Float 转换为 NSNumber

Adding object to NSMutableArray or Converting Float to NSNumber

objective-c

nsmutablearray

nsnumber