This is my NSObject code;
Task.h
#import <Foundation/Foundation.h>
@interface Task : NSObject
@property (nonatomic,strong) NSString *name;
@property (nonatomic,assign) BOOL done;
-(id)initWithName:(NSString *)name done:(BOOL)done;
@end
Task.m
#import "Task.h"
@implementation Task
@synthesize name = _name;
@synthesize done = _done;
-(id)initWithName:(NSString *)name done:(BOOL)done {
    self = [super init];
    if (self) {
        self.name = name;
        self.done = done;
    }
    return self;
}
This is my send mail code
Task *task = [[Task alloc]init];
        MFMailComposeViewController *sendmail = [[MFMailComposeViewController alloc]init];
        [sendmail setMailComposeDelegate:self];
        NSString *message = [_tasks addObject:task]; // Error is here.
        [sendmail setMessageBody:message isHTML:NO];
        [sendmail setSubject:@"Test"];
        [self presentViewController:sendmail animated:YES completion:nil];
I don't know, How to do it. I just want to send the list with mail. Where is my mistake? And How can I fix this?
Tasklistviewcontroller.m
@synthesize tasks = _tasks;
I am transferring from the tasks table view.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *NotDoneCellIdentifier = @"NotDoneTaskCell";
    static NSString *DoneCellIdentifier = @"DoneTaskCell";
    Task *currentTask = [self.tasks objectAtIndex:indexPath.row];
    NSString *cellIdentifier = currentTask.done ? DoneCellIdentifier : NotDoneCellIdentifier;
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier forIndexPath:indexPath];
    // Configure the cell...
    cell.textLabel.text = currentTask.name;
    return cell;
}