UIView 转换为 UIImage 时如何使用自动布局

问题描述

CPOAnnotationView 是 UIView 的一个子视图，我想把 CPOAnnotationView 转换成 UIImage。

- (UIImage*)getimage:(CPOAnnotationViewSize)size {
    CPOAnnotationView* annotationView = [[CPOAnnotationView alloc] initWithFrame:CGRectZero];
    [annotationView setNeedsLayout];
    [annotationView layoutIfNeeded];
    
    CGSize s = annotationView.bounds.size;

    UIGraphicsBeginImageContextWithOptions(s,NO,[UIScreen mainScreen].scale);
    [annotationView.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage*image = UIGraphicsGetimageFromCurrentimageContext();
    UIGraphicsEndImageContext();
    return image;
}

问题是 CPOAnnotationView 具有灵活的宽度，可以包裹它的内容。所以我将 CPOAnnotationView 的框架设置为 CGRectZero。我搜索了stackoverflow，有人说如果你想将uiview转换为uiimage。 uiview 的宽度或高度不能为零。但是我的 CPOAnnotationView 具有灵活的宽度，在设置框架之前计算宽度很复杂。下面是 CPOAnnotationView 的代码

- (instancetype)initWithFrame:(CGRect)frame{
    if (self = [super initWithFrame:frame]){
        self.translatesAutoresizingMaskIntoConstraints = NO;
        
        _titleView = [[UIView alloc] initWithFrame:CGRectZero];
        _titleView.translatesAutoresizingMaskIntoConstraints = NO;
        _titleView.backgroundColor = [UIColor whiteColor];
        [_titleView layoutIfNeeded];
        [self addSubview:_titleView];
        
        NSMutableArray* titleViewConstraints = [NSMutableArray arrayWithCapacity:0];
        [titleViewConstraints addobject:[NSLayoutConstraint constraintWithItem:_titleView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeCenterX multiplier:1.0f constant:0.0f]];
        [titleViewConstraints addobject:[NSLayoutConstraint constraintWithItem:_titleView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0.0f constant:34.0f]];
//        [titleViewConstraints addobject:[NSLayoutConstraint constraintWithItem:_nameLabel attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:_avatarButton attribute:NSLayoutAttributeRight multiplier:1.0f constant:kInnerMesListCellAvatarRightMargin]];
//        [titleViewConstraints addobject:[NSLayoutConstraint constraintWithItem:_nameLabel attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:_dateLabel attribute:NSLayoutAttributeLeft multiplier:1.0f constant:-10.0]];
        [self addConstraints:titleViewConstraints];
        
        UILabel* label = [[UILabel alloc] initWithFrame:CGRectZero];
        label.translatesAutoresizingMaskIntoConstraints = NO;
        label.backgroundColor = [UIColor orangeColor];
        label.textAlignment = NSTextAlignmentCenter;
        label.text = @"1000000";
        label.font = [UIFont systemFontOfSize:16];
        label.textColor = [UIColor blackColor];
        [label layoutIfNeeded];
        [_titleView addSubview:label];
        
        NSMutableArray* labelConstraints = [NSMutableArray arrayWithCapacity:0];
        [labelConstraints addobject:[NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:_titleView attribute:NSLayoutAttributeCenterY multiplier:1.0f constant:0.0f]];
        [labelConstraints addobject:[NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0.0f constant:34.0f]];
        [labelConstraints addobject:[NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:_titleView attribute:NSLayoutAttributeLeft multiplier:1.0f constant:10.0f]];
        [labelConstraints addobject:[NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:_titleView attribute:NSLayoutAttributeRight multiplier:1.0f constant:-10.0f]];
        [_titleView addConstraints:labelConstraints];
    }
    
    return self;
}

下面是我如何调用getimage()方法，我使用getimage()方法创建了一个地图注解，并将注解添加到MapView中

    CPOAnnotation *annotation = [[CPOAnnotation alloc] initWithCoordinate: coordinate  image:[cpoMarker getimage:CPOAnnotationViewSize_Big] content:[cpoMarker content]];
    [self.mapView addAnnotation:annotation];

并在mapview回调方法调用时给MapView添加注解：

- (MAAnnotationView *)mapView:(MAMapView *)mapView viewForAnnotation:(id<MAAnnotation>)annotation {
   if([annotation isKindOfClass:[CPOAnnotation class]]) {
        CPOAnnotation* cpoAnnotation = annotation;
        Nsstring *cpoReuseIndetifier = [Nsstring stringWithFormat:@"%@_%@",@"cpoReuseIndetifier",[cpoAnnotation content]];
        MAAnnotationView *annotationView = [mapView dequeueReusableAnnotationViewWithIdentifier:cpoReuseIndetifier];
        if (annotationView == nil) {
            annotationView = [[MAAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:cpoReuseIndetifier];
        }
        annotationView.image = [cpoAnnotation image];
        return annotationView;
    }
}

解决方法

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