将3个值添加到plist动态，然后一个接一个覆盖一个，如果添加更多

Question

我使用plist在我的应用程序中，我可以将值添加到plist及其工作正常。但我需要的只是3值应该被加入到plist，此后如果尝试添加更多的值应该覆盖前面的三个值上EON后续添加..one由..

这里是我的代码，增加了许多x值：

-(void) myplist :(id) sender 
{ 

NSLog(@"mylist Clicked");  
    NSMutableArray *array = [[NSMutableArray alloc] init]; 

// get paths from root direcory 

NSArray *paths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES); 

// get documents path 

NSString *documentsPath = [paths objectAtIndex:0]; 

NSString *docsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES) objectAtIndex:0]; // get the path to our Data/plist file 
NSLog(docsDir); 

NSString *plistPath = [docsDir stringByAppendingPathComponent:@"Data.plist"]; 

//This copies objects of plist to array if there is one 
[array addObjectsFromArray:[NSArray arrayWithContentsOfFile:plistPath]]; 
[array addObject:searchLabel.text]; 
// This writes the array to a plist file. If this file does not already exist, it creates a new one. 

[array writeToFile:plistPath atomically: TRUE]; 

}

Answer 1

您将需要保存一个变量来存储最后一项插入的索引（lastInsertionIndex below)。假设plist中目前有&第四届一个被插入3项（lastInsertionIndex = 2），代码看起来应该是喜欢 -

// get paths from root direcory 

NSArray *paths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES); 

// get documents path 

NSString *documentsPath = [paths objectAtIndex:0]; 

NSString *docsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES) objectAtIndex:0]; // get the path to our Data/plist file 
NSLog(docsDir); 

    NSString *plistPath = [docsDir stringByAppendingPathComponent:@"Data.plist"]; 

    //This copies objects of plist to array if there is one 
    [array addObjectsFromArray:[NSArray arrayWithContentsOfFile:plistPath]]; 

//If plist has less than 3 items, insert the new item. Don't use lastInsertionIndex. Else, replace one of the items. 
if([array count] < 3) 
{ 
    [array addObject:[searchLabel.text]]; 
} 
else 
{ 
//Update lastInsertionIndex 
lastInsertionIndex++; 
lastInsertionIndex %= 3; // Max size of array = 3 

[array replaceObjectAtIndex:lastInsertionIndex withObject:[searchLabel.text]]; 
} 

[array writeToFile:plistPath atomically: TRUE]; 

HTH，

阿克沙伊