[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object
<pre><code>-(id)init{
    if (self==[super init]) {            
        NSMutableArray *listname = [[NSMutableArray alloc]initWithObjects:@"cu",@"al",@"zn",@"au",@"ru",@"fu",@"rb",@"pb",@"wr", nil];            
        NSMutableArray *listVolumn = [NSMutableArray arrayWithCapacity:[listname count]];           
        for (int i=0; i&lt;[listname count]; i++) {
            [listVolumn addObject:[NSNumber numberWithLong:0]];
        }
        nsmutabledictionary = [[NSDictionary alloc] initWithObjects:listVolumn forKeys:listname];
    }
    return self;
}
</code></pre>

<p>in my init method,I defined two NSMutableArray,and added to NSMutableDictionary nsmutabledictionary.
in my other method:</p>

<pre><code>[nsmutabledictionary setObject:[NSNumber numberWithLong:100] forKey:@"cu"];
</code></pre>

<p>but it crash at above line:
<img src="http://i.stack.imgur.com/u14hu.jpg" alt="enter image description here"></p>
