How to fix x Error parsing XML: unbound prefix in android

Question

I am creating an android application consists of login page, I created login page with two buttons but the xml showing an error called error: Error parsing XML: unbound prefix please tell me how to fix it.?

This is my xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.developer.milanandroid.Login" >

    <LinearLayout
        android:id="@+id/linearLayout1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/linear_1"
        android:layout_alignRight="@+id/linear_1"
        android:layout_below="@+id/linear_1"
        android:layout_marginTop="56dp" >

        <TextView
            android:id="@+id/password"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="PASSWORD :"
            android:textAppearance="?android:attr/textAppearanceMedium" />

        <EditText
            android:id="@+id/editTextusername"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:ems="10"
            android:inputType="textPassword" />
    </LinearLayout>

    <LinearLayout
        android:id="@+id/linear_1"
        android:layout_width="450dp"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="108dp"
        android:orientation="horizontal" >

        <TextView
            android:id="@+id/username"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="USER NAME: "
            android:textAppearance="?android:attr/textAppearanceMedium" />

        <EditText
            android:id="@+id/editTextpassword"
            android:layout_width="350dp"
            android:layout_height="wrap_content" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="450dp"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/linearLayout1"
        android:layout_below="@+id/linearLayout1"
        android:layout_marginTop="63dp" >

        <Button
            android:id="@+id/clear"
            style="?android:attr/buttonStyleSmall"
            android:layout_width="225dp"
            android:layout_height="wrap_content"
            android:text="clear" />

     <!--     <Button
            android:id="@+id/Login"
            style="?android:attr/buttonStyleSmall"
            android:layout_width="225dp"
            android:layout_height="wrap_content"
            android:text="login" />-->
        <com.developer.milanandroid.buttonlib.ActionProcessButton 
            android:id="@+id/btnSignIn"
            android:layout_width="match_parent"
            android:layout_height="48dp"
            android:layout_marginBottom="16dp"
            android:text="Sign_in"
            android:textColor="@android:color/white"
            android:textSize="18sp"
            custom:pb_colorComplete="@color/green_complete"
            custom:pb_colorNormal="@color/blue_normal"
            custom:pb_colorPressed="@color/blue_pressed"
            custom:pb_colorProgress="@color/purple_progress"
            custom:pb_textComplete="Success"
            custom:pb_textProgress="Loading" />

    </LinearLayout>

</RelativeLayout>

Answer 1

add

xmlns:custom="http://schemas.android.com/apk/res-auto"

to your layout.

  <com.developer.milanandroid.buttonlib.ActionProcessButton 
        xmlns:custom="http://schemas.android.com/apk/res-auto"
        android:id="@+id/btnSignIn"