Why can't I turn this object into an instance variable?

I have a object I want to turn into an instance variable. This works:

ZipFile *newZipFile = [[ZipFile alloc] initWithFileName:zipPath mode:ZipFileModeCreate];

But when I try to change it to this it doesn't work:

.h:

@interface PanelController : NSWindowController <NSWindowDelegate> {
  ZipFile *_zipFile;
}
@开发者_C百科property (nonatomic, assign) ZipFile *zipFile;

.m:

@synthesize zipFile = _zipFile;
...
// get a syntax error here
zipFile = [[ZipFile alloc] initWithFileName:zipPath mode:ZipFileModeCreate];

EDIT: I was able to fix this by putting this in my interface and getting rid of the @property:

ZipFile *newZipFile; 

I guess I can't assign setters and getters to just any object? But why won't it work if I do:

ZipFile *zipFile;

There is no ivar named zipFile. Did you mean:

_zipFile = [[ZipFile alloc] initWithFileName:zipPath mode:ZipFileModeCreate];

or:

self.zipFile = [[[ZipFile alloc] initWithFileName:zipPath mode:ZipFileModeCreate] autorelease];

Note: You probably want your property to be retain. assign is for properties you do not own (like delegates). assign properties are unsafe because can easily become dangling pointers.

@synthesize zipFile = _zipFile;
...
// get a syntax error here
zipFile = [[ZipFile alloc] initWithFileName:zipPath mode:ZipFileModeCreate];

Your @synthesize says that your property is named zipFile, but the variable backing it is _zipFile.

You have no zipFile variable, so the assignment line is wrong.

_zipFile = [[ZipFile alloc] initWithFileName:zipPath mode:ZipFileModeCreate];

is correct.