Hi there I have some code at the moment that gives me the error ("0") is not equal to ("50") - condition not applied correctly Basically I am currently using a traditional for loop within a BOOL which goes through the list of items and checks whether or not the condition can be applied, if it can be applied to an item then the BOOL will return YES. I cannot see where I am currently going wrong and need guidance. My code is shown below:
-(BOOL)conditionCanBeApplied:(NSArray *)items{
bool itemConditionCanBeApplied = NO;
for (int i = 0; i < items.count; i++)
{
id myItem = [[items valueForKeyPath:#"itemId"]objectAtIndex: i];
if ([self.applicableItems containsObject:myItem]) {
itemConditionCanBeApplied = YES;
}
}
return itemConditionCanBeApplied;
}
First, don't mix BOOL and bool, they might be very similar but they aren't the same data type. Second, always use fast enumeration if you have a choice. I am assuming in the code below that your items collection is something like an NSArray. Also, there is no reason to test with an if statement just to set a BOOL since the test is a boolean statement. (I am doing it in my example to allow for the break) Lastly, short-circuiting your logic with a break keeps the processor from doing unnecessary work once you have at least one match.
Do something like this:
- (BOOL)conditionTest
{
BOOL itemConditionCanBeApplied = NO;
for (id item in items) {
if ([self.applicableItems containsObject:item]) {
itemConditionCanBeApplied = YES;
break;
}
}
return itemConditionCanBeApplied;
}
Related
I've read somewhere that a variable should be entered into the code if it is reused. But when I write my code for logic transparency, I sometimes create intermediate variables (with names reflecting what they contain) which are used only once.
How incorrect is this concept?
PS:
I want to do it right.
It is important to note that most of the time clarity takes precedence over re-usability or brevity. This is one of the basic principles of clean code. Most modern compilers optimize code anyway so creating new variables need not be a concern at all.
It is perfectly fine to create a new variable if it would add clarity to your code. Make sure to give it a meaningful name. Consider the following function:
public static boolean isLeapYear(final int yyyy) {
if ((yyyy % 4) != 0) {
return false;
}
else if ((yyyy % 400) == 0) {
return true;
}
else if ((yyyy % 100) == 0) {
return false;
}
else {
return true;
}
}
Even though the boolean expressions are used only once, they may confuse the reader of the code. We can rewrite it as follows
public static boolean isLeapYear(int year) {
boolean fourth = year % 4 == 0;
boolean hundredth = year % 100 == 0;
boolean fourHundredth = year % 400 == 0;
return fourth && (!hundredth || fourHundredth);
}
These boolean variables add much more clarity to the code.
This example is from the Clean Code book by Robert C. Martin.
This question already has answers here:
Removing from array during enumeration in Swift?
(9 answers)
Closed 6 years ago.
In this loop we have the potential to reduce the number of items in the loop while processing it. This code works fine in Obj-C, but the Swift loops don't get the message that an item has been removed and end up overflowing the array.
In Objective-C, we had:
for(int i = 4; i < staticBlocks.count; i++)
{
PlayerSprite* spr = [staticBlocks objectAtIndex:i];
[spr setPosition:CGPointMake(spr.position.x, spr.position.y-1)];
if(spr.position.y < -1000)
{
[staticBlocks removeObject:spr];
[spr removeFromParent];
}
if(spr.blockTypeIndex == Block_Type_Power_Up)
{
[spr update];
}
}
In Swift I know of these options:
//for i in 4.stride(to: staticBlocks.count, by: 1){ //crashes
//for i in 4..<staticBlocks.count{ //crashes
for var i = 4; i < staticBlocks.count; i += 1 { //works, but is deprecated
let spr = staticBlocks.objectAtIndex(i) as! PlayerSprite
spr.position = CGPointMake(spr.position.x, spr.position.y-1)
if(spr.position.y < -1000)
{
staticBlocks.removeObject(spr)
spr.removeFromParent()
//break
}
if(spr.blockTypeIndex == k.BlockType.PowerUp)
{
spr.update()
}
}
In this specific case, it really isn't a problem for me to use a break statement (which is currently commented out) to kill the loop and prevent the crash, but it doesn't seem like the proper fix. I assume there will come a time when I need to know how do do this correctly. Is there a non deprecated way to do a for loop, one which processes the count each pass?
A related, unanswered question.
Is the for loop condition evalutaed each loop in swift?
I don't know how to link to a specific answer, but this code did what I needed. Marking as duplicate now.
Removing from array during enumeration in Swift?
var a = [1,2,3,4,5,6]
for (i,num) in a.enumerate().reverse() {
a.removeAtIndex(i)
}
This is because in Swift you cannot remove items from an array while you are iterating over it.
From this question Removing from array during enumeration in Swift?
you can see that you should be using the filter function instead of using a for loop.
For example, don't do this:
for (index, aString: String) in enumerate(array) {
//Some of the strings...
array.removeAtIndex(index)
}
Do something like this:
var theStrings = ["foo", "bar", "zxy"]
// Filter only strings that begins with "b"
theStrings = theStrings.filter { $0.hasPrefix("b") }
(Code example from this answer)
Additionally, it should be noted that filter won't update the array, it will return a new one. You can set your array to be equal to that array afterwards.
An additional way to solve the issue, from the same question is to do this:
var a = [1,2,3,4,5,6]
for (i,num) in a.enumerate().reverse() {
a.removeAtIndex(i)
}
print(a)
I'm making three random choices between two classes, A and B. I need to avoid getting B all three times.
Is there a way to stop arc4random() from giving me that result?
One approach is: If your random routine gives you an unacceptable answer, run it again until it gives you an acceptable answer.
For example, in a solitaire game app of mine, I shuffle a deck and deal some of it into a layout which must be solvable. But what if it isn't solvable? I repeat that: I shuffle the deck again and deal it again. I keep doing that until the layout I've dealt is solvable. All of that happens before the user sees anything, so the user doesn't know what I've been up to behind the scenes to guarantee that the layout makes sense.
In your case, where the possibilities are so limited, another obvious alternative would be this: use a simple combinatorial algorithm to generate beforehand all acceptable combinations of three nodes. Now use arc4random to pick one of those combinations. So, for example:
var list = [[String]]()
let possibilities = ["A","B"]
for x in possibilities {
for y in possibilities {
for z in possibilities {
list.append([x,y,z])
}
}
}
list.removeLast()
Now list is an array of all possible triples of "A" or "B", but without ["B","B","B"]. So now pick an element at random and for each of its letters, if it is "A", use class A, and if it is "B", use class B. (Of course I suppose we could have done this with actual classes or instances, but it seems simplest to encode it as letters.)
BOOLs and loops to the rescue...
BOOL classA = false;
BOOL classB = false;
for (int i=0; i<3; i++) {
int r = arc4random() % 2;
if(i < 2) {
if(r == 0) {
NSLog(#"Class A");
classA = true;
} else {
NSLog(#"Class B");
classB = true;
}
} else {
if(classA == false)
NSLog(#"Class A");
if(classB == false)
NSLog(#"Class B");
}
}
The 2 BOOLs guarantee that each class has at least one member for each 3 cycle run.
m_cAppIdMap is an object of a dictionary.
I want to iterate through the dictionary and to ind and remove the value pEvent.wTimerId is an unsigned short integer that is stored as key in the dictionary.
if(unsigned short* key in m_cAppIdMap) //error:Expected expression before 'unsigned'
{
(void)[self findAndRemoveEvent:pEvent];
(void)CFDictionaryRemoveValue(m_cAppIdMap,&wTimerId);
free(pEvent);
bReturn = YES;
}
I am getting an error when i try to iterate through the loop.
EDITED
-(BOOL)KillTimer:(unsigned short)wTimerId
{
stRs232Timer* pEvent;
BOOL bReturn=FALSE;
theLock = [[NSLock alloc]init];
if ([theLock tryLock]) {
// if ( m_cAppIdMap.Lookup(wTimerId,pEvent) )
// {
// (void)findAndRemoveEvent(pEvent); // remove from event queue
// (void)m_cAppIdMap.RemoveKey(wTimerId); // remove from app map
for(wTimerId in m_cAppIdMap)
{
(void)[self findAndRemoveEvent:pEvent];
(void)CFDictionaryRemoveValue(m_cAppIdMap,&wTimerId);
free(pEvent);
bReturn = YES;
}
[theLock unlock];
}
return bReturn;
}
I am getting error in this code 'selector element does not have a valid object type' . I need to search for wTimerId(key) in the m_cAppIdMap. Is it what i'm doing is correct.The commented lines above the for loop is the implementation of the same code in cpp. I coud not make the same logic over here in Objective C.
I think you meant to use for rather than if. Additionally, the fast enumeration syntax
for (x in y) can only be used on objects that implement the NSFastEnumeration protocol—typically NSArray. It looks like you're using C arrays, so this syntax won't work anyway.
you meant to write for (VARIABLE in CONTAINER) {...} -- but your sample uses if, not for.
side note: it is an error to mutate the collections you iterate over during the iteration.
I want to make a selection before apply one of two animations,
what I thought is: make a Point one, if my myImageView is at the Point one, then apply animationNo1, else apply animationNo2, but I got this:"used struct type value where scalar is required", at line if (myImageView.layer.position = one)
What I do? how can I fix this?
Does anyone know exactly what makes the problem happen?
CGPoint one = CGPointMake(myImageView.layer.position.x, 100);
if (myImageView.layer.position = one)
{
animationNo1
}
else
{
animationNo2
}
First of all, your if-statement will not do what you think. If you want to compare something you have to use == (ie 2 =)
and you can't compare CGPoints like this.
use
if (CGPointEqualToPoint(one, self.view.layer.position))
if (myImageView.layer.position = one) { animationNo1 }
should be
if (CGPointIsEqualToPoint(myImageView.layer.position, one)) { animationNo1 }
You used a single = meaning assignment, rather than a == for comparison. But the == wouldn't do what you wanted here anyway.
You are passing a struct (int this case position) instead of a scalar. To do what you want you need to use CGPointIsEqualToPoint:
if (CGPointEqualToPoint(one, self.view.layer.position))
Full code with corrections:
CGPoint one = CGPointMake(myImageView.layer.position.x, 100);
if (CGPointEqualToPoint(one, self.view.layer.position))
{
animationNo1
}
else
{
animationNo2
}
Also, as others have pointed out: Be careful about = vs ==. They are different. In this case you don't use == for comparison fortunately, but if you use = for other stuff it will make it true instead of checking to see if it is true.