如何在NSArray中存储浮点值? [英] How can I store a float value in an NSArray?
问题描述
for ( tempI = 0; tempI < 10; tempI++ )
{
tempJ = 1;
NSArray *objectsForArray = [NSArray arrayWithObjects:@"array[tempI][tempJ]", @"array[tempI][tempJ+1]", @"array[tempI][tempJ+2]", nil];
}
我可以写上面的代码。我需要在 NSArray
中存储一个浮点值(array [] [])
。我可以这样做吗?
我的问题是,我有一个矩阵
Can I write the code as above. I need to store an float value (array[][])
in NSArray
. Can I do it ?
My problem is, I have a matrix as
1.0 0.4 0.3 0.5
2.0 0.4 0.5 0.5
3.0 4.3 4.9 0.5
我需要检索值0.4,0.3,0.5),使用1.0,2.0,3.0。我如何使用NSDictionary为此?
谢谢
I need to retrieve values (0.4, 0.3, 0.5) using 1.0, 2.0 3.0 . How can I use NSDictionary for this?
Thank You
for( tempI = 0; tempI < 5; tempI++)
{
NSDictionary *dictionary[tempI] = [ [NSDictionary alloc] initWithObjects:@"array[tempI][tempI + 1]", @"array[tempI][tempI + 2]", @"array[tempI][tempI + 3]", @"array[tempI][tempI + 4]", @"array[tempI][tempI + 5]", nil];
}
我可以这样写吗?目标C接受吗?
Can I write in this way ? Does Objective C accepts it ?
我收到了错误
error: variable-sized object may not be initialized
推荐答案
NSArray只能存储对象,而不是基元,幸运的是,NSNumber类有一个方便的方法,它接受一个float基元,并返回一个float对象:
NSArray can only store objects, not primitives, fortunatly, the NSNumber class has a convenience method that takes a float primitive and returns a float object as such:
+ (NSNumber *)numberWithFloat:(float)value
$ b b
因此你可以这样填充你的数组:
therefore you could populate your array like this:
float exampleFloat = 5.4;
NSArray *anArrayOfFloatObjects = [NSArray arrayWithObjects:
[NSNumber numberWithFloat:10.0],
[NSNumber numberWithFloat:2],
[NSNumber numberWithFloat:4],
[NSNumber numberWithFloat:exampleFloat],
nil]; // Don't forget the nil to signal
// end of the array
对于您的特定问题,您可以写:
As for your specific issue, you could write:
NSMutableArray *tmpArray; // this is necessary since an NSArray can only be initialized
// once and we will need to have all the objects that will be
// added to the array available to us at once.
tmpArray = [NSMutableArray arrayWithCapacity:12]; // returns an autoreleased empty array
for (int col=0; col<=3; col++) {
for (int row=0; row<=2; row++) {
[tmpArray addObject:[NSNumber numberWithFloat:array[col][row]]];
}
}
NSArray *myArray = [NSArray arrayWithArray:tmpArray];
至于使用字典来检索矩阵值,我唯一能想到的是键编码您的矩阵值如下:
as far as using a dictionary to retrive matrix values, the only way I can think off would be to key code your matrix values as such:
A1 A2 A3 A4
A1 A2 A3 A4
B1 B2 B3 B4
B1 B2 B3 B4
C1 C2 C3 C4
C1 C2 C3 C4
D1 D2 D3 D4
D1 D2 D3 D4
示例:
NSMutableDictionary *myDictionary;
[myDictionary setObject:[NSNumber numberWithFloat:5.0] forKey:@"A1"];
...
NSNumber *myFloat = [myDictionary objectForKey:@"A1"];
此外,重要的是要指出, ,它字面上是一个NSString对象。所以当你写:
Also, it is important to point here that whenever something is written under the format @"something here", it literally is an NSString object. so when you write:
NSArray *objectsForArray = [NSArray arrayWithObjects:
@"array[tempI][tempJ]",
@"array[tempI][tempJ+1]",
@"array[tempI][tempJ+2]",
nil];
这与写入完全一样:
NSString *newString = @"Roses are red"; // example strings
NSString *newString1 = @"Violets are blue";
NSString *newString2 = @"array[tempI][tempJ+1]";
NSString *newString3 = @"These are all string objects";
NSArray *objectsForArray = [NSArray arrayWithObjects:
@"array[tempI][tempJ]",
newString2,
@"array[tempI][tempJ+2]",
nil];
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