Question

背景：这是我的第二部iphone应用程序，但我已经完成了其他类型的编码。

我正在通过本教程创建iOS音乐播放器应用： Build an iOS Music Player

情况非常好：到目前为止，我可以填充一张包含iPhone播放列表的表格。我可以选择一个播放列表，获取该播放列表的持久ID，并使用它在下一页上创建查询，该页面用该播放列表中的所有歌曲填充表格，并显示歌曲的数量和总分钟数。

只要您只传递一个变量（在本例中为专辑名称），本教程中的代码就可以运行 - 这在教程中给出了：

- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    AlbumViewController *detailViewController = [segue destinationViewController];

    MPMediaQuery *albumsQuery = [MPMediaQuery albumsQuery];
    NSArray *albums = [albumsQuery collections];

    int selectedIndex = [[self.tableView indexPathForSelectedRow] row];
    MPMediaItem *selectedItem = [[albums objectAtIndex:selectedIndex] representativeItem];
    NSString *albumTitle = [selectedItem     valueForProperty:MPMediaItemPropertyAlbumTitle];
//THIS IS WHAT'S PASSING THE VARIABLE                     
    [detailViewController setAlbumTitle:albumTitle];
}

我已将其更改为此 - 以便能够使用播放列表，因为我发现使用持久性ID比制定结果查询的名称更有效（此代码有效）：

- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    PlaylistSongsViewController *varLetsSegueOhYeah = [segue destinationViewController];
    //what are we even looking at again? it's a query
    MPMediaQuery *playlistsQuery = [MPMediaQuery playlistsQuery];
    //identify the query again please?
    NSArray *playlists = [playlistsQuery collections];
    //where are we in the table
    int selectedIndex = [[self.tableView indexPathForSelectedRow] row];
    //for that index id, what playlist does that map to
    MPMediaItem *selectedItem = [playlists objectAtIndex:selectedIndex];
    //for that playlist, what is its name
    //NSString *varPlaylistName = [selectedItem     valueForProperty:MPMediaPlaylistPropertyName];
    //for that playlist, what is its persistent id
    NSString *varPlaylistID = [selectedItem     valueForProperty:MPMediaPlaylistPropertyPersistentID];
//THIS IS WHAT'S PASSING THE VARIABLE
    [varLetsSegueOhYeah setVarPlaylistID:varPlaylistID];
}

然而，我希望能够传递两个变量 - 持久性ID和播放列表名称，因此我可以在目标屏幕的顶部显示它。您可以在上面的代码中看到实际抓取播放列表名称的行被注释掉了 - 这是因为显然如果您抓住了值但实际上并没有使用它，那么应用程序就会崩溃。但它可以向您展示如果我知道如何使用它将会是什么样子。这两个变量都在目标屏幕的ViewController.h中正确声明。

我已经搜索了各种猜测和组合，但到目前为止还没有任何工作。总而言之 - 我知道如何发送1个变量，现在我该如何发送2个？

编辑：目标屏幕代码

PlaylistSongsViewController.m 从这样开始：

#import "PlaylistSongsViewController.h"

@interface PlaylistSongsViewController ()

@end

@implementation PlaylistSongsViewController
@synthesize varPlaylistName;
@synthesize varPlaylistID;
- (void)viewDidLoad
{
    [super viewDidLoad];

    self.title = varPlaylistName;
}

其余部分可以在＆＃34;第3步：显示专辑歌曲＆amp;中找到here。信息＆＃34;除了我已经取代＆＃34;专辑＆＃34;用＆＃34;播放列表＆＃34;。

PlaylistSongsViewController.h：

#import <UIKit/UIKit.h>
#import <MediaPlayer/MediaPlayer.h>

@interface PlaylistSongsViewController : UITableViewController
{
    NSString *varPlaylistName;
    NSString *varPlaylistID;
}
//albumTitle in tutorial

@property NSString *varPlaylistName;
@property NSString *varPlaylistID;

@end

Answer 1

您可以根据需要设置任意数量的变量：

[varLetsSegueOhYeah setVarPlaylistID:varPlaylistID];
[varLetsSegueOhYeah setVarPlaylistName:varPlaylistName];

您也可以直接访问该物业：

varLetsSegueOhYeah.varPlaylistID = varPlaylicstID;
varLetsSegueOhYeah.varPlaylistName = varPlaylistName;

然后在viewDidLoad：

NSLog(@"varPlaylistID = %@",self.varPlaylistID);
NSLog(@"varPlaylistName = %@",self.varPlaylistName);

确保在接口文件中声明属性：

@property (nonatomic , strong) NSString* varPlaylicstID;
@property (nonatomic , strong) NSString* varPlaylistName;

请注意，您不需要像过去那样合成您的属性，它现在就会自动完成。

Answer 2

试试这个：

if ([segue.destinationViewController respondsToSelector:@selector(setVarPlaylistID:)]) {

        [segue.destinationViewController setVarPlaylistID:varPlaylistID];
        [segue.destinationViewController setVarPlaylistName:varPlaylistName];
        [segue.destinationViewController setAnotherVariable:variableNameOfCorrectType];

} else NSLog(%@"Segue does not respond to selector");

在destinationViewController中，您必须如此声明和合成：

NSString* varPlaylistID;
.
.
.
@synthesize varPlaylistID = _varPlaylistID;

//Declare setter
-(void) setVarPlaylistID:(NSString *)varPlaylistID
{
_varPlaylistID = varPlaylistID;
}

对varPlaylistName执行相同的操作。

Answer 3

好的 - 我终于开始工作了。我发现了我的问题：

我没有意识到我们并没有那么多＆＃34;传递全局变量＆＃34;因为我曾经把它们当作独立的信息包围。他们是更多类似的表单字段附加到每个对象类型和我们发送填写说明。
因为我认为我的混乱思维过程让编译器感到困惑。
摆脱＆＃34; @ synthesize＆＃34;后，我无法弄清楚它何时需要＆＃34; _＆＃34;在财产名称之前以及何时需要＆＃34; self。＆＃34;。我排序通过反复试验和更清楚地完成了这一点关于概念上发生了什么的想法。
1. 我没有意识到我在编译器中设置了断点，导致它在UI中挂起，否则就不会。糟糕。

New PlaylistsController.h文件：

#import <UIKit/UIKit.h>
#import <MediaPlayer/MediaPlayer.h>

@interface PlaylistsViewController : UITableViewController


@property (nonatomic, retain) NSString *varSelectedPlaylistID;
@property (nonatomic, retain) NSString *varSelectedPlaylistName;


@end

这说明我们将要找出用户为播放列表ID和播放列表名称选择的值。

New PlaylistSongsController.h：

#import <UIKit/UIKit.h>
#import <MediaPlayer/MediaPlayer.h>

@interface PlaylistSongsViewController : UITableViewController

@property (nonatomic, retain) NSString *varPlaylistIDToDisplay;
@property (nonatomic, retain) NSString *varPlaylistNameToDisplay;

@end

这说明我们将使用某些值来显示特定的播放列表名称和ID。

新播放列表控制器PrepareForSegue：

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    //First - identify what the user has selected.

    //define query
    MPMediaQuery *playlistsQuery = [MPMediaQuery playlistsQuery];
    //dump query results into array
    NSArray *playlists = [playlistsQuery collections];

    //identify user selected table row
    int selectedIndex = [[self.tableView indexPathForSelectedRow] row];
    //map user selected table row to array item
    MPMediaItem *selectedItem = [playlists objectAtIndex:selectedIndex];


    //assign selected values to properties of the object we're looking at right now. They have underscores here for some reason!
    _varSelectedPlaylistID = [selectedItem valueForProperty:MPMediaPlaylistPropertyPersistentID];
    _varSelectedPlaylistName = [selectedItem valueForProperty:MPMediaPlaylistPropertyName];


    //now let's get ready to go. for an object of type "Playlist Songs View Controller, we want to create a new instance of that and name it MyNewPlaylistInstance and then go to there.
    PlaylistSongsViewController *MyNewPlaylistInstance = [segue destinationViewController];

    //when we get to MyNewPlaylistInstance, it will want to know which playlist ID and name to use - tell it to use the values we just set
    MyNewPlaylistInstance.varPlaylistIDToDisplay = self.varSelectedPlaylistID;
    MyNewPlaylistInstance.varPlaylistNameToDisplay = self.varSelectedPlaylistName;
}

    @end

使用多个变量准备ForSegue

3 个答案: