# FlexboxLayout
FlexboxLayout is a library project which brings the similar capabilities of
[CSS Flexible Box Layout Module](https://www.w3.org/TR/css-flexbox-1) to Android.

## Installation
You have two options to install the library. You can choose either of:

(1) Add the following dependency to your `build.gradle` file
(At this moment not available from jcenter)
TODO(thagikura): Upload the library to jCenter

(2) Use the GitHub source and include that as a module dependency by following steps
* Clone this library, parallel to your own application project:
```
git clone https://github.com/google/FlexboxLayout
```

* In the root of your application's project, edit the `settings.gradle` and add the following lines:
```
include ':FlexboxLayout'
project(':FlexboxLayout').projectDir = new File('../FlexboxLayout/')
```

* In your application's main module, edit your `build.gradle` to add a new dependency:
```
dependencies {
    ...
    compile project(':FlexboxLayout')
 }
```

## Usage
FlexboxLayout extends the ViewGroup like LinearLayout and RelativeLayout.
You can specify the attributes from a layout XML like:
```xml
<com.google.android.libraries.flexbox.FlexboxLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:flexWrap="wrap"
    app:alignItems="stretch"
    app:alignContent="stretch" >

    <TextView
        android:id="@+id/textview1"
        android:layout_width="120dp"
        android:layout_height="80dp"
        app:layout_flexBasisPercent="50%"
        />

    <TextView
        android:id="@+id/textview2"
        android:layout_width="80dp"
        android:layout_height="80dp"
        app:layout_alignSelf="center"
        />

    <TextView
        android:id="@+id/textview3"
        android:layout_width="160dp"
        android:layout_height="80dp"
        app:layout_alignSelf="flex_end"
        />
</com.google.android.libraries.flexbox.FlexboxLayout>
```

Or from code like:
```java
FlexboxLayout flexboxLayout = (FlexboxLayout) findViewById(R.id.flexbox_layout);
flexboxLayout.setFlexDirection(FlexboxLayout.FLEX_DIRECTION_COLUMN);

View view = flexboxLayout.getChildAt(0);
FlexboxLayout.LayoutParams lp = (FlexboxLayout.LayoutParams) view.getLayoutParams();
lp.order = -1;
lp.flexGrow = 2;
view.setLayoutParams(lp);
```

## Supported attributes
You can specify following attributes for the FlexboxLayout.
* flexDirection
  * The direction children items are placed inside the Flexbox layout, it determines the
  direction of the main axis (and the cross axis, perpendicular to the main axis).
  Possible values are:
    * row (default)
    * row_reverse
    * column
    * column_reverse

    ![Flex Direction explanation](/assets/flex-direction.gif)

* flexWrap
  * This attribute controls whether the flex container is single-line or multi-line, and the
  direction of the cross axis. Poissble values are:
    * nowrap (default)
    * wrap
    * wrap_reverse

    ![Flex Wrap explanation](/assets/flex-wrap.gif)

* justifyContent
  * This attribute controls the alignment along the main axis. Possible values are:
    * flex_start (default)
    * flex_end
    * center
    * space_between
    * space_around

    ![Justify Content explanation](/assets/justify-content.gif)

* alignItems
  * This attribute controls the alignment along the cross axis. Possible values are:
    * stretch (default)
    * flex_start
    * flex_end
    * center
    * baseline

    ![Align Items explanation](/assets/align-items.gif)

* alignContent
  * This attribute controls the alignment of the flex lines in the flex container. Possible values
  are:
    * stretch (default)
    * flex_start
    * flex_end
    * center
    * space_between
    * space_around

    ![Align Content explanation](/assets/align-content.gif)

Also you can specify following attributes for the children of a FlexboxLayout

* layout_order
  * This attribute can change the ordering of the children views are laid out.
  By default, children are displayed and laid out in the same order as they appear in the
  layout XML. If not specified, `1` is set as a default value.

* layout_flexGrow
  * This attribute determines how much this child will grow if positive free space is
  distributed relative to the rest of other flex items included in the same flex line.
  If not specified, `0` is set as a default value.

* layout_flexShrink
  * This attributes determines how much this child will shrink is negative free space is
  distributed relative to the rest of other flex items included in the same flex line.
  If not specified, `1` is set as a default value.

* layout_alignSelf
  * This attributes determines the alignment along the cross axis (perpendicular to the
  main axis). The alignment in the same direction can be determined by the
  `alignItems` in the parent, but if this is set to other than
  `auto`, the cross axis alignment is overridden for this child. Possible values are:
    * auto (default)
    * flex_start
    * flex_end
    * center
    * baseline
    * stretch

* layout_flexBasisPercent
  * The initial flex item length in a fraction format relative to its parent.
  The initial main size of this child View is trying to be expanded as the specified
  fraction against the parent main size.
  If this value is set, the length specified from `layout_width`
  (or `layout_height`) is overridden by the calculated value from this attribute.
  This attribute is only effective when the parent's length is definite (MeasureSpec mode is
  `MeasureSpec.EXACTLY`). The default value is `-1`, which means not set.

## Known differences from the original CSS specification
This library tries to achieve the same capabilities of the original
[Flexible specification](https://www.w3.org/TR/css-flexbox-1) as much as possible,
but due to some reasons such as the way specifying attributes can't be the same between
CSS and Android XML, there are some known differences from the original specification.

(1) There is no [flex-flow](https://www.w3.org/TR/css-flexbox-1/#flex-flow-property)
equivalent attribute
  * Because `flex-flow` is a shorthand for setting the `flex-direction` and `flex-wrap` properties,
  specifying two attributes from a single attribute is not practical in Android.

(2) There is no [flex](https://www.w3.org/TR/css-flexbox-1/#flex-property) equivalent attribute
  * Likewise `flex` is a shorthand for setting the `flex-grow`, `flex-shrink` and `flex-basis`,
  specifying those attributes from a single attribute is not practical.

(3) `layout_flexBasisPercent` is introduced instead of
  [flexBasis](https://www.w3.org/TR/css-flexbox-1/#flex-basis-property)
  * Both `layout_flexBasisPercent` in this library and `flex-basis` property in the CSS are used to
  determine the initial length of an individual flex item. The `flex-basis` property accepts width
  values such as `1em`, `10px` and the `content` as string as well as percentage values such as
  `10%`, `30%` whereas `layout_flexBasisPercent` only accepts percentage values.
  But specifying initial fixed width values can be done by specifying width (or height) values in
  layout_width (or layout_height, varies depending on the `flexDirection`). Also the same
  effect can be done by specifying "wrap_contnet" in layout_width (or layout_height) if
  developers want to achieve the same effect as 'content'. Thus, `layout_flexBasisProperty` only
  accepts percentage values, which can't be done through layout_width (or layout_height) for
  simplicity.

(4) min-width and min-height can't be specified
  * Which isn't just implemented yet.

## How to make contributions
Please read and follow the steps in CONTRIBUTING.md

## License
Please see License