如何将浮点值存储在 NSArray 中? [英] How can I store a float value in an NSArray?
问题描述
for ( tempI = 0; tempI <10; tempI++ ){温度J = 1;NSArray *objectsForArray = [NSArray arrayWithObjects:@"array[tempI][tempJ]", @"array[tempI][tempJ+1]", @"array[tempI][tempJ+2]", nil];}我可以像上面那样写代码吗?我需要在 NSArray 中存储一个浮点值 (array[][]).我可以吗?
我的问题是，我有一个矩阵作为
1.0 0.4 0.3 0.52.0 0.4 0.5 0.53.0 4.3 4.9 0.5我需要使用 1.0, 2.0 3.0 检索值 (0.4, 0.3, 0.5).我该如何使用 NSDictionary?
谢谢你
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?Objective C 接受它吗?
我收到一个错误
<块引用>错误:可变大小的对象可能没有被初始化NSArray 只能存储对象，不能存储基元，幸运的是，NSNumber 类有一个方便的方法，它接受一个浮点基元并返回一个浮点对象，如下所示:
+ (NSNumber *)numberWithFloat:(float)value因此你可以像这样填充你的数组:
float exampleFloat = 5.4;NSArray *anArrayOfFloatObjects = [NSArray arrayWithObjects:[NSNumber numberWithFloat:10.0],[NSNumber numberWithFloat:2],[NSNumber numberWithFloat:4],[NSNumber numberWithFloat:exampleFloat],零];//不要忘记 nil 来表示信号//数组结束至于你的具体问题，你可以写:
NSMutableArray *tmpArray;//这是必要的，因为 NSArray 只能被初始化//一次，我们需要拥有所有的对象//立即添加到我们可用的数组中.tmpArray = [NSMutableArray arrayWithCapacity:12];//返回一个自动释放的空数组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];就使用字典来检索矩阵值而言，我能想到的唯一方法是对矩阵值进行键编码:
A1 A2 A3 A4
B1 B2 B3 B4
C1 C2 C3 C4
D1 D2 D3 D4
例如:
NSMutableDictionary *myDictionary;[myDictionary setObject:[NSNumber numberWithFloat:5.0] forKey:@"A1"];...NSNumber *myFloat = [myDictionary objectForKey:@"A1"];此外，重要的是在这里指出，每当以 @"something here" 格式编写某些内容时，它实际上就是一个 NSString 对象.所以当你写的时候:
NSArray *objectsForArray = [NSArray arrayWithObjects:@"数组[tempI][tempJ]",@"数组[tempI][tempJ+1]",@"数组[tempI][tempJ+2]",零];这和写完全一样:
NSString *newString = @"玫瑰是红色的";//示例字符串NSString *newString1 = @"紫罗兰色是蓝色的";NSString *newString2 = @"array[tempI][tempJ+1]";NSString *newString3 = @"这些都是字符串对象";NSArray *objectsForArray = [NSArray arrayWithObjects:@"数组[tempI][tempJ]",新字符串2，@"数组[tempI][tempJ+2]",零];for ( tempI = 0; tempI < 10; tempI++ )
{
tempJ = 1;
NSArray *objectsForArray = [NSArray arrayWithObjects:@"array[tempI][tempJ]", @"array[tempI][tempJ+1]", @"array[tempI][tempJ+2]", nil];
}
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
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];
}
Can I write in this way ? Does Objective C accepts it ?
I am getting an error as
error: variable-sized object may not be initialized
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
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
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];
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
B1 B2 B3 B4
C1 C2 C3 C4
D1 D2 D3 D4
for example:
NSMutableDictionary *myDictionary;
[myDictionary setObject:[NSNumber numberWithFloat:5.0] forKey:@"A1"];
...
NSNumber *myFloat = [myDictionary objectForKey:@"A1"];
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];
this is exactly the same as writting:
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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