NSLayoutConstraint

自己实践出来的，写个总结。

+ (instancetype)constraintWithItem:(id)view1 attribute:(NSLayoutAttribute)attr1 relatedBy:(NSLayoutRelation)relation toItem:(nullableid)view2 attribute:(NSLayoutAttribute)attr2 multiplier:(CGFloat)multiplier constant:(CGFloat)c;

此方法各参数：

第一个参数:指定约束的视图view1

第二个参数:指定view1的属性attr1

第三个参数:指定左右两边的视图的关系relation

第四个参数:指定约束右边的视图view2

第五个参数:指定view2的属性attr2

第六个参数:指定一个与view2属性相乘的乘数multiplier

第七个参数:指定一个与view2属性相加的浮点数c

属性说明：

目前为用过的有

    NSLayoutAttributeLeft -->左边约束

    NSLayoutAttributeRight-->右边约束

    NSLayoutAttributeTop-->上边约束

    NSLayoutAttributeBottom-->下边约束

    NSLayoutAttributeLeading-->左边约束

    NSLayoutAttributeTrailing-->又边约束

    NSLayoutAttributeWidth-->宽度约束

    NSLayoutAttributeHeight-->高度约束

    NSLayoutAttributeCenterX-->水平约束

    NSLayoutAttributeCenterY-->垂直约束

relation说明：  

    NSLayoutRelationLessThanOrEqual-->小于等于

    NSLayoutRelationEqual -->等于

    NSLayoutRelationGreaterThanOrEqual -->大于等于

依据的公式是：view1.attr1 = view2.attr2*m +c

以下是自定义几个ScrollView随window的大小变化而变化。

int customColumn = 4;    int customRow =4;    NSMutableArray *customviewArray = [[NSMutableArrayalloc] initWithCapacity:0];    for (int i =0; i< 4; i++) {        for (int j=0; j < 4; j++) {            NSScrollView *aview = [NSScrollViewnew];            [aview setTranslatesAutoresizingMaskIntoConstraints:NO];            [_myviewaddSubview:aview];            NSLayoutConstraint *bottom ;            if (i ==0) {                bottom = [NSLayoutConstraintconstraintWithItem:aviewattribute:NSLayoutAttributeBottomrelatedBy:NSLayoutRelationEqualtoItem:_myviewattribute:NSLayoutAttributeBottommultiplier:1.0fconstant:-1.0f];            }else{                //                CustomSlotView *bottomview = [customviewArray objectAtIndex:i*customColumn+j-customColumn];                NSScrollView *bottomview = [customviewArrayobjectAtIndex:i*customColumn+j-customColumn];                bottom = [NSLayoutConstraintconstraintWithItem:aviewattribute:NSLayoutAttributeBottomrelatedBy:NSLayoutRelationEqualtoItem:bottomview attribute:NSLayoutAttributeTopmultiplier:1.0fconstant:-10.0f];                //                [bottomview removeConstraints:[bottomview constraints]];            }            NSLayoutConstraint *top ;            if (i == customRow -1) {                top = [NSLayoutConstraintconstraintWithItem:aviewattribute:NSLayoutAttributeToprelatedBy:NSLayoutRelationEqualtoItem:_myviewattribute:NSLayoutAttributeTopmultiplier:1.0fconstant:0.0f];            }                        NSLayoutConstraint *left;            if (j ==0) {                left = [NSLayoutConstraintconstraintWithItem:aviewattribute:NSLayoutAttributeLeadingrelatedBy:NSLayoutRelationEqualtoItem:_myviewattribute:NSLayoutAttributeLeadingmultiplier:1.0fconstant:1.0f];            }else{                //                CustomSlotView *leftview = [customviewArray objectAtIndex:i*customColumn+j-1];                NSTextView *leftview = [customviewArrayobjectAtIndex:i*customColumn+j-1];                left = [NSLayoutConstraintconstraintWithItem:aviewattribute:NSLayoutAttributeLeadingrelatedBy:NSLayoutRelationEqualtoItem:leftview attribute:NSLayoutAttributeTrailingmultiplier:1.0fconstant:10.0f];                //                [leftview removeConstraints:[leftview constraints]];            }            NSLayoutConstraint *right;            if (j == customColumn -1) {                right = [NSLayoutConstraintconstraintWithItem:aviewattribute:NSLayoutAttributeTrailingrelatedBy:NSLayoutRelationEqualtoItem:_myviewattribute:NSLayoutAttributeTrailingmultiplier:1.0fconstant:0.0f];            }            NSLayoutConstraint *width;            NSLayoutConstraint *height;            if (i*customColumn + j >0) {                //                CustomSlotView *nextView = [customviewArray objectAtIndex:i*customColumn+j-1];                NSTextView *nextView = [customviewArrayobjectAtIndex:i*customColumn+j-1];                width = [NSLayoutConstraintconstraintWithItem:aviewattribute:NSLayoutAttributeWidthrelatedBy:NSLayoutRelationEqualtoItem:nextView attribute:NSLayoutAttributeWidthmultiplier:1.0fconstant:0.0f];                height = [NSLayoutConstraintconstraintWithItem:aviewattribute:NSLayoutAttributeHeightrelatedBy:NSLayoutRelationEqualtoItem:nextView attribute:NSLayoutAttributeHeightmultiplier:1.0fconstant:0.0f];                //                [nextView removeConstraints:[nextView constraints]];            }                        bottom.active =YES;                        top.active =YES;                        left.active =YES;            right.active =YES;                        height.active =YES;            width.active =YES;            [customviewArray addObject:aview];        }            }