Implementing auto layout for views generated progr

问题:

I have an app whose views are generated programmatically. Example:

-(void)loadView
{
    [super loadView];

// SET TOP LEFT BTN FOR NEXT VIEW
UIBarButtonItem *topLeftBtn = [[UIBarButtonItem alloc] initWithTitle:@"Back" style:UIBarButtonItemStyleBordered target:nil action:nil];
self.navigationItem.backBarButtonItem = topLeftBtn;
[topLeftBtn release];

// programmatically set up the view for cart tableView
CGRect iouTableViewFrame = CGRectMake(0, 0, 320, 348);
iouTableView = [[UITableView alloc]initWithFrame:iouTableViewFrame style:UITableViewStylePlain];
[[self iouTableView] setDelegate:self];
[[self iouTableView] setDataSource:self];
[[self view] addSubview:iouTableView];

// set up the summary label
CGRect summaryTableFrame = CGRectMake(0, 348, 320, 18);
UILabel *summaryTableLabel = [[UILabel alloc] initWithFrame:summaryTableFrame];
[summaryTableLabel setFont:[UIFont fontWithName:@"Helvetica" size:14]];
[summaryTableLabel setText:@"   Summary"];
UIColor *labelColor = UIColorFromRGB(MiddleBlueColor);
[summaryTableLabel setBackgroundColor:labelColor];
[summaryTableLabel setTextColor:[UIColor whiteColor]];
[[self view] addSubview:summaryTableLabel];

// set up the summary table
CGRect summaryTableViewFrame = CGRectMake(0, 366, 320, 44);
summaryTableView = [[UITableView alloc]initWithFrame:summaryTableViewFrame style:UITableViewStylePlain];
[summaryTableView setScrollEnabled:NO];
[[self summaryTableView] setDelegate:self];
[[self summaryTableView] setDataSource:self];
[[self view] addSubview:summaryTableView];
}

Yes. I will update to NIBs and use interface builder and storyboard in the future but I have not done ios programming in a year.

With the new iPhone 5 having a different screen size, the app just does not look good and I need to implement auto layout of some sort. Is there a way to do it programmatically for now instead of using IB?

Thanks much!

回答1:

Yes there is, by using two methods in NSLayoutConstraint

-(NSArray*)constraintsWithVisualFormat:options:metrics:views:
-(NSLayoutConstraint*)constraintWithItem:attribute:relatedBy:toItem:attribute:
    multiplier:constant:

The visual format language is all packaged up into an NSString So I'll take your iouTableView for example.

[self.view addConstraints:[NSLayoutConstraint 
    constraintsWithVisualFormat:@"|[iouTableView]|" 
    options:0 
    metrics:nil 
    views:NSDictionaryOfVariableBindings(iouTableView)]];

The pipe symbol "|" represents the superview's edge. The [] represent a view. So what we did there was we hooked the iouTableView's left and right edge to the left and right edge of its superview.

Another example of the visual format: Let's hook your table view, summary label and summary table vertically.

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:
    @"V:|[iouTableView(348)][summaryTableLabel(18)][summaryTableView(44)]"
    options:NSLayoutFormatAlignAllLeft
    metrics:nil
    views:NSDictionaryOfVariableBindings(iouTableView, summaryTableLabel, summaryTableView)]];

Now this links up all three views vertically on each of their edges, NSLayoutFormatAlignAllLeft tells all the views to align left and they'll do so based on other constraints, in this case, the previous constraint. The ()s are used to specify the size of the views.

There's a bit more like inequalities and priorities as well as the "-" spacer symbol but check out the apple docs for that

Edit: Corrected the examples to use constraintsWithVisualFormat as shown in the method signature.

回答2:

In addition to Aplle provided methods you can use Parus lib for operating with AutoLayout from code.

For example you will be able to specify:

PVVFL(@"[view1]-20-[view2]").fromRightToLeft.withViews(views).asArray

Instead of

[NSLayoutConstraint constraintsWithVisualFormat:@"[view1]-20-[view2]"
                                        options:NSLayoutFormatDirectionRightToLeft
                                        metrics:nil
                                          views:views]

Also you will be able to group layouts settings, mix VFL and not VFL constraints. Parus able to prevent common mistakes, differentiate location and parameters constriaints, and provide great auto-completion support.