Original subtitles

0 Now it's all very well and good using a container to lay out a single widget, such as a piece of text 1

or a image. And we can define it padding, its margin, its size, its background color etc.. 2

But what if you had lots of different things that you want to lay out relative to each other? 3

Well, in that case, you need something that can take lots of children, and not just a single one. 4

And the easiest way to do this is using columns and rows, so that we can lay out our widgets in a vertical 5

direction or a horizontal direction, and determine how they should be sized. 6

Going back to our widgets catalog and looking specifically at the layout widgets, we're gonna go down 7

to the multi-child layout widget section. And you can see the most commonly used ones to layout multiple 8

child widgets, are rows and columns. Rows go horizontal, columns will go vertical. Let's go ahead and create 9

a column of our own. 10

What if instead of only having a single container, I had lots of different containers? So I'm going to 11

go ahead and get rid of the margin and padding, so we don't confuse ourselves, and I'm gonna name it 12

Container 1. 13

So here's Container 1, and it's white. 14

And I'm gonna collapse my container. So you can see that all the code that's related to setting the properties 15

of our container, is all enclosed in these parentheses. When I click on it, I can expand it. But I can also 16

compress it like this. Instead of having the child of our safe area, 17

So what's inside our safe area being just a container, 18

I'm going to cut that and paste it down here, for a little bit later on. And instead the child is going 19

to be a column. Now a column crucially, doesn't have a child. 20

It has children, because we can put lots of things inside our column. And it's got this angle bracket 21

to tell you that this is actually a list of items that we can put in here. 22

We can put lots of widgets in between these square brackets. And what we're going to start with is that 23

container that we moved out just now. 24

So I'm gonna hit COMMAND + X to cut and paste it in here, and then I'm gonna collapse it down. 25

And at this point when I hit save, you'll see that nothing much really happens on screen because we have 26

a column that only really comes into action when you have more than one widget. 27

Let's leave our first container and let's build another container as the second child of our column. 28

Now this container is again going to have a width of 100 and a height of 100. And notice that 29

when you add a comma to the end of say you know every line, and you hit save, it makes it really easy 30

for Dart to know how to lay out your code. 31

Let us also give our container a color so that we can actually see it. 32

So let's change this to a blue color. 33

And hit save. And you can see we now have two containers onscreen, and I'm going to give this a child which 34

is a piece of text, and I'm going to tell it to write the words 'Container 2'. So we have container 1 and 35

container 2. 36

And I'm simply going to copy this container to create a third one. 37

And our third one is going to be red. And it's going to be container 3. 38

So now we have three containers all a 100 by 100. 39

All with different colors, and it's being laid out in a vertical direction. Which is because, we have all 40

the containers inside a column. Now our columns will automatically try and take up as much of the vertical 41

space as possible. 42

So if we go into Flutter Inspector and we check out what the column actually looks like, you can see 43

it's this box right here. 44

It's trying to take up all of the space that is available vertically. But horizontally, 45

it's limiting itself to the size of its children. 46

We can change this however. 47

We can change its mainAxisSize, and main axis for a column, is of course vertical. 48

So let's change this to the minimum size. 49

And you can see now, when I hit save, my column actually shrinks to be the size that's only required to 50

fit my three containers, all of its children. 51

Currently, our column is laying out its children from top to bottom, so container 1, 2 and 3. 52

Now what if we wanted to go the other direction instead? 53

Well, we can change its vertical direction. 54

We can either change it to go up, which means it goes from the bottom to the top. 55

So here's 1, 2 and 3 . Or we can change it as down, which is the default, where it goes from top 56

to bottom. 57

Now what if you didn't want to change the direction of it, but instead you wanted to change the spacing 58

between our containers. 59

Well then you would use something called mainAxisAlignment, and by default all of our containers are 60

aligned to the start. 61

So it's mainAlignment.start. 62

And this will try and place the children as close to the start of the main axis as possible. 63

So this is a vertical axis, 64

and this is the start of the vertical axis. 65

However we can also change it to end. 66

So if we had MainAxisAlignment.end then our containers will all be bunched down here, towards the 67

end of our main axis. 68

Now you can also move it all to the center. And you can use a variety of these to determine how you want 69

your screen to be laid out. 70

Now what if we didn't actually want all of our children to be bunched together like this, at the center 71

at the start or at the end. What if we wanted them to be spread out a bit more. 72

Well we can use something that's called 'spaceEvenly.' 73

And this will calculate the amount of free space that the column has, and it'll space all of our children 74

evenly throughout the column. 75

But what if we wanted something to be at the start and something to be at the bottom, and then another 76

one in the center? 77

Well we would then use spaceBetween instead. 78

Now what if I wanted to change the way that my containers are aligned on the horizontal axis? 79

Well in this case, instead of using the main axis alignment property, I would be using something called 80

the cross axis alignment. 81

And this is a cross or perpendicular to the main axis. 82

So for columns, they'll be the horizontal. 83

Now here, I also have access to the start CrossAxisAlignment, and also end CrossAxisAlignment. 84

But you'll notice that if I just go ahead and put this in, and I hit save to hot reload, nothing really 85

happens on the horizontal axis. 86

And the reason for this is that my axis alignment is actually trying to align to my children. 87

So that means that say, if I had a child that was much wider, let's say 300 across, then all 88

of my children will align themselves to the right edge of each other. 89

But if they're all the same size, then they're already aligned on the end, so they won't pop over to the 90

right side. 91

In this case. 92

Now if you wanted all your three containers to go over to the right, one way of doing this might be creating 93

simply a invisible container, where you give it a width of infinity, and to give it a width of infinity, 94

we write double.infinity 95

And what this will do, is it will create a container down here. 96

You can see it has no height. 97

So it's just got a width, and it's as wide as the screen will allow it to be. 98

So if I give it a small height so that you can see it more easily, in this case, it's just this last bit. 99

It doesn't have a color. 100

So it's completely invisible but it pushes all of our children to the right, because we're now all aligning 101

to the end of our column on the horizontal axis 102

and one of our containers is as wide as the screen allows now. 103

What if instead of doing this, you wanted actually to stretch all your containers, so that they fill the 104

entire width? 105

Now you could provide a width for each of the containers, to be double.infinity 106

So let's change the width to 107

So now, all of my containers will stretch to the entire width that's possible. But there's a much easier 108

way of doing this actually, by using a property that comes with our column. And instead of using Cross 109

AxisAlignment.end, we can use CrossAxisAlignment.stretch. And this will stretch our children so that 110

they can be the best versions of themselves, or in this case, actually stretch them across the screen. 111

So you can see that even though I've reloaded, everything looks exactly the same. 112

And I no longer need to provide a width property for my containers because it's being stretched by its 113

parent, the column. 114

Now what if you wanted a little bit of spacing between your containers. Because at the moment, they're 115

all very much in each other's business 116

and right next to each other with no space in between. 117

Well if you knew exactly how much space you want to have between your containers, you can use a Sized 118

box. And a sized box can have a height and width of course. 119

But in the case of where it's being put inside a column, which is aligned vertically, then we only really 120

need to provide a height. So we can give it a height of 20, and leave it width property as zero. 121

And you can see, this goes in here between container 1 and container 2, and gives us a little bit of spacing 122

between those two things. 123

And it helps us when we want a little bit of space between our children. Now, 124

everything that I've spoken about columns also apply to rows. 125

So in fact, I can straight up just change our column to a row, and you'll see it does exactly the same 126

thing on the horizontal axis. 127

So in this case though, we're saying that the cross axis alignment. 128

So for a row, the main axis of is of course horizontal but the cross axis alignment. 129

So the vertical alignment has to be stretched so all our containers are stretched vertically. 130

And for all the children, they each have a height which doesn't really get taken into account anymore 131

because it's being stretched, but we can also give it a width for example. 132

So let's say we give it a width of 30 for the first one. 133

You can see that gets affected, because my containers are being aligned on the horizontal axis. 134

Now you can see that my sized box disappeared, because I'm giving it a height but that doesn't really 135

matter when it doesn't have a width. 136

So in a row, in order to give it space, we're gonna be using a sized box with a width in order to give 137

it a little bit of spacing. 138

So the best way of getting to know columns and rows and containers is really to try it out for yourself. 139

So in the next lesson, I've got a challenge for you. 140

I've got a layout that I want you to replicate using containers, columns and rows and everything that 141

we've learned about so far. 142

Now while you're playing around with this, as humans, we tend to be quite visual. And it's usually easier 143

for us to see what something will do before actually writing out the code. 144

So I recommend pulling up this Flutter layout cheat sheet that's created by Tomek, and all of course 145

linked to it in the course resources. And what he's done, is he's taken things such as the column and 146

row, and he's tried to show you what it looks like before you write the code. 147

So in this case, when you use main Alignment.start on a column, 148

this is what it looks like. When you use main alignment don't start on a row, 149

this is what it looks like. And you can see that he's put in all of the things that we've talked about, 150

at least for columns and rows, and you can identify it visually before you commit it into writing the 151

code. In order to complete the challenge, head over to the next lesson and check out the layout 152

I want you to achieve. And then go ahead and write the code yourself, and see if you can make it work 153

and make it look exactly the same. 154

So, I'll see you on the next lesson.