YieldLayout

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Language
Java
Version
N/A
Created
Jul 18, 2014
Updated
Jul 22, 2014 (Retired)
Owner
Evan Tatarka (evant)
Contributor
Evan Tatarka (evant)
1
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YieldLayout

Have you ever had to create two almost-identical layout files because they had a few minor differences? Sure, you can fix it with <include/> but then you start ending up with layouts all over the place.

YieldLayout to the rescue! It works opposite of <include/> so you can combine one layout around another instead of inside it. After it does it's magic, you will have 0 extra views in your layout hierarchy, just like <include/>, so it's like it was never there.

Usage

You can create a layout file that has places to yield content.

<!-- yield_view.xml -->
<?xml version="1.0" encoding="utf-8"?>

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <me.tatarka.yieldlayout.Yield
        android:id="@+id/first"
        android:layout_weight="1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    <View
        android:layout_width="match_parent"
        android:layout_height="1dp"
        android:background="@color/divider_black"
        />

    <TextView
        android:layout_weight="1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/between"
        android:gravity="center"
        android:textSize="@dimen/text_display_2"
        android:textColor="@color/text_black"
        />

    <View
        android:layout_width="match_parent"
        android:layout_height="1dp"
        android:background="@color/divider_black"
        />

    <me.tatarka.yieldlayout.Yield
        android:id="@+id/second"
        android:layout_weight="1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
</LinearLayout>

Then you can create another file that uses that layout, filling in the yields.

<!-- use_yield.xml -->
<?xml version="1.0" encoding="utf-8"?>

<me.tatarka.yieldlayout.YieldLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    app:yield_layout="@layout/yield_linear_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="@string/first"
        android:textColor="@color/text_black"
        android:textSize="@dimen/text_display_2"
        />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/second"
        android:textColor="@color/text_black"
        android:textSize="@dimen/text_display_2"
        android:gravity="center"
        />

</me.tatarka.yieldlayout.YieldLayout>

By default child views are matched against Yields in the order they are defined. However, if you give your child views explicit id's, they will be matched against the Yield id's.

<?xml version="1.0" encoding="utf-8"?>

<me.tatarka.yieldlayout.YieldLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    app:yield_layout="@layout/yield_linear_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <!-- This one will appear second -->
    <TextView
        android:id="@+id/second"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/second"
        android:textColor="@color/text_black"
        android:textSize="@dimen/text_display_2"
        android:gravity="center"
        />

    <!-- This one will appear first -->
    <TextView
        android:id="@+id/first"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="@string/first"
        android:textColor="@color/text_black"
        android:textSize="@dimen/text_display_2"
        />
</me.tatarka.yieldlayout.YieldLayout>

ListViews

If you want to use this in a list adapter, you can't use the YieldLayout directly because it will try to add it's layout to it's parent which a listview doesn't allow. Instead, you can use YieldLayoutInflater which will return the final view to add instead of the YieldLayout.

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    if (convertView == null) {
        int layout = getItemViewType(position) == 0 ? R.layout.list_item_1 : R.layout.list_item_2;  
        convertView = YieldLayoutInflater.from(mContext).inflate(layout, parent, false);
    }
    return convertView;
}

Or if you are changeing the outer layout instead of the child views,

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    if (convertView == null) {
        int layout = getItemViewType(position) == 0 ? R.layout.layout_1 : R.layout.layout_2;  
        convertView = YieldLayoutInflater.from(mContext).inflate(R.layout.list_item, layout, parent, false);
    }
    return convertView;
}

Different numbers of children

You may be wondering what happens if you don't specify as many child views for YieldLayout as there are Yields. Too many children is an error because there is no way to know where to put the extra ones. Too few, however, will simply cause the extra Yields to be removed.

Sometimes, however, you may depend on the Yield to correctly layout your views. For example,

<RelativeLayout
  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="wrap_content">

    <TextView
         android:id="@+id/content"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_above="@+id/footer"/>

    <me.tatarka.yieldlayout.Yield
        android:id="@+id/footer"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"/>
</RelativeLayout>

If there is no matching child for footer, then it will be removed, and content won't lay out correctly. To fix this, you can add

    <me.tatarka.yieldlayout.Yield
      app:yield_keep_if_empty="true"/>

which will keep the Yield view even if it's not replaced. Note that in this case, the Yield view will always have a size of 0.

Layout Preview

The layout preview in Android Studio will show Yield placholder views so that you can see how they fit in your layout. If you define your yield_layout for your YieldLayout, that will correctly show as well.

If you are setting your yield_layout dynamically, you would think you could preview it by setting tools:yield_layout in your xml. Unfortunately, the tools namespace doesn't work with custom attributes. To get around this, you can set app:tools_yield_layout instead which will give an equivalent result.