我一直在开发一个编程，用户可以从弹出按钮中选择一个字段列表，然后按一个计算按钮，然后根据选择，将一串文本输出到UIText字段。
但是，当用户在按下选择按钮之前开始在弹出按钮中选择其他选项时，我希望清除文本字段。
无论如何这是可能的吗？
答案 0 :(得分：0)
恰好在发生这种情况的地方使用此代码：
Undefined symbols for architecture x86_64:
"ArrayBag<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >::getIndexOf(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) const", referenced from:
ArrayBag<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >::remove(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) in main.o
"ArrayBag<int>::getIndexOf(int const&) const", referenced from:
ArrayBag<int>::remove(int const&) in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
#ifndef _ARRAY_BAG
#define _ARRAY_BAG
#include "BagInterface.h"
#include <vector>
template<class ItemType>
class ArrayBag : public BagInterface<ItemType>
{
private:
static const int DEFAULT_CAPACITY = 24; // the bag size a bit bigger to allow
// adding bags.
ItemType items[DEFAULT_CAPACITY]; // Array of bag items
int itemCount; // Current count of bag items
int maxItems; // Max capacity of the bag
// Returns either the index of the element in the array items that
// contains the given target or -1, if the array does not contain
// the target.
int getIndexOf(const ItemType& target) const;
public:
ArrayBag();
int getCurrentSize() const;
bool isEmpty() const;
bool add(const ItemType& newEntry);
void clear();
bool remove(const ItemType& anEntry);
bool contains(const ItemType& target) const;
int getFrequencyOf(const ItemType& anEntry) const;
ArrayBag<string> merge(ArrayBag<string> a, ArrayBag<string> b);
std::vector<ItemType> toVector() const;
#include "ArrayBag.h"
#include <cstddef>
template<class ItemType>
ArrayBag<ItemType>::ArrayBag(): itemCount(0), maxItems(DEFAULT_CAPACITY)
{
} // end default constructor
template<class ItemType>
int ArrayBag<ItemType>::getCurrentSize() const
{
return itemCount;
} // end getCurrentSize
template<class ItemType>
bool ArrayBag<ItemType>::isEmpty() const
{
return itemCount == 0;
} // end isEmpty
template<class ItemType>
bool ArrayBag<ItemType>::add(const ItemType& newEntry)
{
bool hasRoomToAdd = (itemCount < maxItems);
if (hasRoomToAdd)
{
items[itemCount] = newEntry;
itemCount++;
} // end if
return hasRoomToAdd;
} // end add
template<class ItemType>
void ArrayBag<ItemType>::clear()
{
itemCount = 0;
} // end clear
template<class ItemType>
bool ArrayBag<ItemType>::remove(const ItemType& anEntry)
{
int locatedIndex = getIndexOf(anEntry);
bool canRemoveItem = !isEmpty() && (locatedIndex > -1);
if (canRemoveItem)
{
itemCount--;
items[locatedIndex]=items[itemCount];
}//end if
return canRemoveItem;
} //end remove
template<class ItemType>
bool ArrayBag<ItemType>::contains(const ItemType& anEntry) const
{
bool found = false;
int curIndex = 0; //current array index
while(!found && (curIndex < itemCount))
{
if(anEntry == items[curIndex])
{
found = true;
} //end if
curIndex++; //increment to the next entry
} //end while
return found;
}
template<class ItemType>
int ArrayBag<ItemType>::getFrequencyOf(const ItemType& anEntry) const
{
int frequency = 0;
int curIndex = 0; //current index array
while(curIndex < itemCount)
{
if (items[curIndex] == anEntry)
{
frequency++;
} //end if
curIndex++; //incremenet to next entry
} //end while
return frequency;
} //end getFrequencyOf
template<class ItemType>
vector<ItemType> ArrayBag<ItemType>::toVector() const
{
vector<ItemType> bagContents;
for (int i = 0; i < itemCount; i++)
bagContents.push_back(items[i]);
return bagContents;
} // end toVector
#include <iostream>
#include <string>
#include "ArrayBag.h"
#include "ArrayBag.cpp"
using namespace std;
void displayBag(ArrayBag<string>& bag)
{
cout << "The bag contains " << bag.getCurrentSize()
<< " items:" << endl;
vector<string> bagItems = bag.toVector();
int numberOfEntries = (int)bagItems.size();
for (int i = 0; i < numberOfEntries; i++)
{
cout << bagItems[i] << " ";
} // end for
cout << endl << endl;
} // end displayBag
void displayBag(ArrayBag<int>& bag)
{
cout << "The bag contains " << bag.getCurrentSize()
<< " items:" << endl;
vector<int> bagItems = bag.toVector();
int numberOfEntries = (int)bagItems.size();
for (int i = 0; i < numberOfEntries; i++)
{
cout << bagItems[i] << " ";
} // end for
cout << endl << endl;
} // end displayBag
int sumOfBag(ArrayBag<int>& aBag)
{
int sum=0;
vector<int> aBagvector = aBag.toVector();
int numberOfEntries = (int) aBagvector.size();
for (int i = 0; i < numberOfEntries; i++)
{
sum += aBagvector[i];
}
//cout << "The sum of the bag is " << sum << endl;
return sum;
}
void bagTester(ArrayBag<string>& bag)
{
cout << "isEmpty: returns " << bag.isEmpty()
<< "; should be 1 (true)" << endl;
displayBag(bag);
string items[] = {"one", "two", "three", "four", "five", "one"};
cout << "Add 6 items to the bag: " << endl;
for (int i = 0; i < 6; i++)
{
bag.add(items[i]);
} // end for
displayBag(bag);
cout << "isEmpty: returns " << bag.isEmpty()
<< "; should be 0 (false)" << endl;
cout << "getCurrentSize: returns " << bag.getCurrentSize()
<< "; should be 6" << endl;
cout << "Try to add another entry: add(\"extra\") returns "
<< bag.add("extra") << endl;
displayBag(bag);
} // end bagTester
int main()
{
ArrayBag<string> bag;
cout << "Testing the Array-Based Bag:" << endl;
cout << "The initial bag is empty." << endl;
bagTester(bag);
ArrayBag<string> bag_of_strings1;
string items[] = {"tom","dick","harry"};
for (int i=0; i<3; i++) {bag_of_strings1.add(items[i]);}
displayBag(bag_of_strings1);
ArrayBag<string> bag_of_strings2;
string new_items[] = {"now","is","the","time","for","all"};
for(int i=0; i<6; i++){
bag_of_strings2.add(new_items[i]);
}
displayBag(bag_of_strings2);
//ArrayBag<string> newbag=merge(bag_of_strings1,bag_of_strings2);
//displayBag(newbag);
ArrayBag<int> bag_of_ints;
int array_of_ints[]={6,7,85,9,12,15};
for (int i=0;i<6;i++){
bag_of_ints.add(array_of_ints[i]);
}
displayBag(bag_of_ints);
cout<<sumOfBag(bag_of_ints)<<endl;
return 0;
} // end main