将float转换为NSNumber

Question

我在这里缺少一些基本的东西.一定忘记了.但基本上,我有以下代码,目的是采用NSNumber,将其转换为float,将其乘以2并将结果返回给NSNumber.我在最后一步得到一个错误,我很难过.我该怎么办

NSNumber *testNSNumber = [[[NSNumber alloc] initWithFloat:200.0f] autorelease];
float myfloatvalue = [testNSNumber  floatValue] * -2;
NSLog(@" Test float value %1.2f \n\n",myfloatvalue);
[testNSNumber floatValue:myfloatvalue];  // error here is floatValue is not found

Answer 1

该方法floatValue的NSNumber不带参数.如果要设置新的浮点数,则需要重新分配testNSNumber,因为NSNumber没有可变对应项:

testNSNumber = @(myfloatvalue); // The new syntax

要么

testNSNumber = [NSNumber numberWithFloat: myfloatvalue]; // The old syntax

Answer 2

Swift 3.0:

let testNSNumber: NSNumber = NSNumber(value: myfloatvalue)