Question

首先，系统自动删除正确的约束，以便一切按预期工作，但我想了解如何使我的代码更好。 Uitableview正在iOS 8.0自动模式下工作，并没有实现heightforindexpath方法。

uitableview在uitableviewcells中显示图像，我只是想在uiimageview中添加一个比率约束，以便正确显示图像。它似乎按预期工作，但可能有一些我不理解的东西（方法的顺序或约束没有在适当的时候给出我不确定）。

以下是您可以查看的代码的一部分。图像宽度和高度存储在数据库中，用于在下载图像之前设置约束。

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

PostImageTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifierPostImage];

if (cell == nil) {
cell = [[PostImageTableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifierPostImage]; }

// Adding image         
[cell.imagePost setImageWithURL:[NSURL URLWithString:[[self.myData objectAtIndex:indexPath.row] valueForKey:@"image"]] placeholderImage:[UIImage imageNamed:@""]];
// Adding constraint    
[cell setConstraints:[[[self.myData objectAtIndex:indexPath.row] valueForKey:@"imageWidth"] doubleValue] withHeight:[[[self.myData objectAtIndex:indexPath.row] valueForKey:@"imageHeight"] doubleValue]];

return cell;
}

PostImageTableViewCell自定义类的setConstraints方法在这里。我想要实现的是删除给前一个单元格的旧约束，并在下一个单元格中为新图像添加新约束...但是根据我从日志中理解它似乎不会那样做。是混合约束还是我必须给比率数字更清洁？

- (void)setConstraints:(double)width withHeight:(double)height {

    int fullWidth = [[UIScreen mainScreen] applicationFrame].size.width;

    [self.imagePost removeConstraint:self.imageConstraint];
    self.imageConstraint = [NSLayoutConstraint constraintWithItem:self.imagePost attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.imagePost attribute:NSLayoutAttributeHeight multiplier:(MAX(width,(fullWidth-20))/height) constant:0.0];
    [self.imagePost addConstraint:self.imageConstraint];
}

错误讯息。它似乎不喜欢给出的比率约束......再次，它在模拟器/设备中正确显示，但我想了解我做错了什么。

Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSLayoutConstraint:0x7fb80cbac720 V:|-(11.5)-[CustLabelWithPadding:0x7fb80cb66240'JUL 20 - 18:39']   (Names: '|':UITableViewCellContentView:0x7fb80cb8bfd0 )>",
    "<NSLayoutConstraint:0x7fb80cbac7c0 V:[CustLabelWithPadding:0x7fb80cb66240'JUL 20 - 18:39'(23)]>",
    "<NSLayoutConstraint:0x7fb80cbac580 V:[CustLabelWithPadding:0x7fb80cb66240'JUL 20 - 18:39']-(11.5)-[CustLabelWithPadding:0x7fb80b90d8e0'Tr']>",
    "<NSLayoutConstraint:0x7fb80cbac8c0 V:[CustLabelWithPadding:0x7fb80b90d8e0'Tr'(>=34.5)]>",
    "<NSLayoutConstraint:0x7fb80cbac840 V:[CustLabelWithPadding:0x7fb80b90d8e0'Tr']-(1)-[CustLabelWithPadding:0x7fb80cba83e0'Rr']>",
    "<NSLayoutConstraint:0x7fb80cbac9e0 V:[CustLabelWithPadding:0x7fb80cba83e0'Rr'(>=34.5)]>",
    "<NSLayoutConstraint:0x7fb80cbac910 V:[CustLabelWithPadding:0x7fb80cba83e0'Rr']-(1)-[UIImageView:0x7fb80cba8a20]>",
    "<NSLayoutConstraint:0x7fb80cbaca30 V:[UIImageView:0x7fb80cba8a20]-(1)-[UIView:0x7fb80cba8c20]>",
    "<NSLayoutConstraint:0x7fb80cbacc00 V:[UIView:0x7fb80cba8c20(50.6)]>",
    "<NSLayoutConstraint:0x7fb80cbacb80 V:[UIView:0x7fb80cba8c20]-(11.5)-|   (Names: '|':UITableViewCellContentView:0x7fb80cb8bfd0 )>",
    "<NSLayoutConstraint:0x7fb80cbb0130 H:[UIImageView:0x7fb80cba8a20(352)]>",
    "<NSLayoutConstraint:0x7fb80cbb2080 UIImageView:0x7fb80cba8a20.width == 1.65647*UIImageView:0x7fb80cba8a20.height>",
    "<NSLayoutConstraint:0x7fb80cbabf60 'UIView-Encapsulated-Layout-Height' V:[UITableViewCellContentView:0x7fb80cb8bfd0(392.5)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7fb80cbb2080 UIImageView:0x7fb80cba8a20.width == 1.65647*UIImageView:0x7fb80cba8a20.height>

我清理了一下代码，但基本上可用的宽度是375-20 * 1.15。图像高度为212.5（存储在数据库中的数字），因此最终比率为352 / 212.5 = 1.65647 ...如错误消息中所示。另一个约束工作正常，我认为它们用于没有图像的单元格，我没有错误信息。

Answer 1

实际上，如果你尝试进行数学计算，我们最终会错过0.1 ...最小刻度是半个点，系统最终找不到相同的高度总和。我用高度约束替换了比率约束，并确保我给出了一个合适的高度（没有＆＃34;奇怪的数字＆＃34;）

[self.contentView removeConstraints:self.imageConstraints];
double ratio = (MAX(width,(fullWidth-20*multiplier))/height);
double newHeight = floor((fullWidth / ratio) / 0.5 + 1) * 0.5;

NSDictionary *viewsDic = @{@"imagePost":self.imagePost};
self.imageConstraints = [NSLayoutConstraint constraintsWithVisualFormat:[NSString stringWithFormat:@"V:[imagePost(%f)]",newHeight] options:0 metrics:0 views:viewsDic];
[self.contentView addConstraints:self.imageConstraints];

正如你所看到的那样，newHeight被修改了，所以我们最终得到了一个很好的＆＃34;系统会喜欢的号码。这删除了我所有的约束问题。实际上，50.6的高度也是如此。使用相同的等式，我确保发送51而不是50.6。

使用uiimageview无法同时满足uitableviewcell中的约束

1 个答案: