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Question

这是一个简单的项目，我正在从书中复制一半来自学。这是一个待办事项列表，包括表格视图，文本字段和用于将任务添加到列表的按钮。然后它将任务数组保存到目录中（使用辅助函数），当您关闭并重新打开应用程序时，它会检索信息。东西在计算机上运行，​​我认为它也在设备上工作，直到我关闭应用程序并重新打开它以发现阵列中没有任何元素。因为它在电脑上工作，我不知道什么是不对的。我理解的一些代码，我刚刚复制的一些代码（如帮助函数），任何建议都非常感谢！ P

代码：

h file

#import <UIKit/UIKit.h>

NSString *docPath();

@interface ViewController : UIViewController<UITableViewDataSource>

{
    UITableView *taskTable;
    UITextField *taskField;
    UIButton *insertButton;

    NSMutableArray *tasks;

}

- (void)addTask:(id)sender;

- (void)writeTasksToFile:(NSString *)path;

@end

m file

#import "ViewController.h"

NSString *docPath()
{
    NSArray *pathList = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

    return [[pathList objectAtIndex:0] stringByAppendingString:@"data.td"];
}

@interface ViewController ()

@end


@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    NSArray *plist = [NSArray arrayWithContentsOfFile:docPath()];
    if(plist) {
        tasks = [plist mutableCopy];
    } else {
        tasks = [[NSMutableArray alloc] init];
    }

    CGRect buttonFrame = CGRectMake(228,40,72,31);
    insertButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [insertButton setFrame:buttonFrame];
    insertButton.backgroundColor = [UIColor redColor];
    [insertButton addTarget:self action:@selector(addTask:) forControlEvents:UIControlEventTouchUpInside];
    [insertButton setTitle:@"Insert" forState:UIControlStateNormal];
    [[self view] addSubview:insertButton];

    CGRect tableFrame = CGRectMake(0, 80, 320, 380);
    taskTable = [[UITableView alloc] initWithFrame:tableFrame style:UITableViewStylePlain];
    [taskTable setSeparatorStyle:UITableViewCellSeparatorStyleNone];
    taskTable.separatorStyle = UITableViewCellSeparatorStyleSingleLine;
    [self.view addSubview:taskTable];
    [taskTable setDataSource:self];

    CGRect fieldFrame = CGRectMake(20, 40, 200, 31);
    taskField = [[UITextField alloc]initWithFrame:fieldFrame];
    [taskField setBorderStyle:UITextBorderStyleRoundedRect];
    [taskField setPlaceholder:@"type a task, enter"];
    [taskField setBackgroundColor:[UIColor greenColor]];
    [self.view addSubview:taskField];


    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(applicationDidEnterBackground:) name:UIApplicationDidEnterBackgroundNotification object:nil];

}

- (void) applicationDidEnterBackground:(UIApplication *)application {
    [tasks writeToFile:docPath() atomically:YES];

}

- (void)addTask:(id)sender{

    NSString *t = [taskField text];

    if ([t isEqualToString:@""]) {return;}

    [tasks addObject:t];
    [taskTable reloadData];
    [taskField setText:@""];
    [taskField resignFirstResponder];

}



- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{

    return [tasks count];
}

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath

{
    if (editingStyle == UITableViewCellEditingStyleDelete)
    {
        [tasks removeObjectAtIndex:indexPath.row];

        [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
    } 
}

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{

    UITableViewCell *c = [taskTable dequeueReusableCellWithIdentifier:@"Cell"];

    if (!c){
        c = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"Cell"];
    }

    NSString *item = [tasks objectAtIndex:[indexPath row]];
    [[c textLabel] setText:item];

    return c;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


- (void)writeTasksToFile:(NSString *)path
{
    [tasks writeToFile:path atomically:YES];
}

@end

编辑---------------------------------------------- -------------------------------------------------- ------------------------------

这是一个调试器屏幕截图，在该行上有一个断点，用于检查是否有一个plist。

Answer 1

我看到需要改变的一件事是你的docPath()正在回归一条糟糕的道路。您需要使用stringByAppendingPathComponent代替stringByAppendingString

return [[pathList objectAtIndex:0] stringByAppendingPathComponent:@"data.td"];

或者，如果您想使用stringByAppendingString，那么它应该是：

return [[pathList objectAtIndex:0] stringByAppendingString:@"/data.td"];