iOS成长之AutoLayout写控件的注意事项

本篇博客主要总结，在使用AutoLayout写控件时的注意事项。

Step 1，重写+ (BOOL)requiresConstraintBasedLayout； 方法，返回YES。这样默认就是使用自动布局。

- (BOOL)requiresConstraintBasedLayout
{
return YES;
}

Step 2，组件位置，样式变化等

1. 重写- (void)updateConstraints；组件位置，大小的变化在这个方法里面写。

- (void)updateConstraints {
重写对view写约束

//according to apple super should be called at end of method
[super updateConstraints];
}

触发方法

- (void)toggleButtonPosition {
// tell constraints they need updating
[self setNeedsUpdateConstraints];

// update constraints now so we can animate the change
[self updateConstraintsIfNeeded];

// 使用UIView animateWithDuration 实现动画的效果
[UIView animateWithDuration:0.4 animations:^{
[self layoutIfNeeded];
}];
}

下面是代码事例。摘自Masonry iOS Examples

//
//  MASExampleRemakeView.m
//  Masonry iOS Examples
//
//  Created by Sam Symons on 2014-06-22.
//  Copyright (c) 2014 Jonas Budelmann. All rights reserved.
//

#import "MASExampleRemakeView.h"

@interface MASExampleRemakeView ()

@property (nonatomic, strong) UIButton *movingButton;
@property (nonatomic, assign) BOOL topLeft;

- (void)toggleButtonPosition;

@end

@implementation MASExampleRemakeView

- (id)init {
self = [super init];
if (!self) return nil;

self.movingButton = [UIButton buttonWithType:UIButtonTypeSystem];
[self.movingButton setTitle:@"Move Me!" forState:UIControlStateNormal];
self.movingButton.layer.borderColor = UIColor.greenColor.CGColor;
self.movingButton.layer.borderWidth = 3;

[self.movingButton addTarget:self action:@selector(toggleButtonPosition) forControlEvents:UIControlEventTouchUpInside];
[self addSubview:self.movingButton];

self.topLeft = YES;

return self;
}

+ (BOOL)requiresConstraintBasedLayout
{
return YES;
}

// this is Apple's recommended place for adding/updating constraints
- (void)updateConstraints {

[self.movingButton remakeConstraints:^(MASConstraintMaker *make) {
make.width.equalTo(@(100));
make.height.equalTo(@(100));

if (self.topLeft) {
make.left.equalTo(self.left).with.offset(10);
make.top.equalTo(self.top).with.offset(10);
}
else {
make.bottom.equalTo(self.bottom).with.offset(-10);
make.right.equalTo(self.right).with.offset(-10);
}
}];

//according to apple super should be called at end of method
[super updateConstraints];
}

- (void)toggleButtonPosition {
self.topLeft = !self.topLeft;

// tell constraints they need updating
[self setNeedsUpdateConstraints];

// update constraints now so we can animate the change
[self updateConstraintsIfNeeded];

[UIView animateWithDuration:0.4 animations:^{
[self layoutIfNeeded];
}];
}

@end