How to make layout to be 80% of the width of the screen?

Question

How can I make some layout to be for example 80% or 90% of the width of the screen, no matter what is the screen size or DPI? I tried with " but I get 80% of the height then.

EDIT:

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="@drawable/background" >

    <Button
        android:id="@+id/bNivoi1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_marginTop="80dp"
        android:background="@drawable/button_nivoi_back" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:weightSum="1"
        android:orientation="horizontal" >

    <TextView
        android:id="@+id/tvOpis15Nivoa"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:gravity="center"
        android:textSize="15sp"
        android:layout_weight="0.8"
        android:text="text" />
    </LinearLayout>

</LinearLayout>

I only need textview to be 80% of the screen, not the rest of the activity.

Answer 1

android:layout_weight is based on the android:orientation of your LinearLayout - if you want your layout to take up 80% of the width, you need a LinearLayout with an android:orientation="horizontal"

<LinearLayout
    android:id="@+id/your_outer_layout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical" > <!-- note that vertical is the default -->

    <!-- Other elements here -->

    <LinearLayout
        android:id="@+id/eighty_percent_layout_holder
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:weightSum="1">
        <View
            android:id="@+id/your_eighty_percent_layout"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="0.8" />
     </LinearLayout>

    <!-- Other elements here -->
</LinearLayout>