Level List

Definition

A resource that manages a number of alternate Drawables.

It’s inflated into the LevelListDrawable java object.

Each drawable is assigned a maximum numerical level.

You can set the level value of the object with setLevel(int) or an equivalent method.

This will load the image/drawable whose maximum level attribute you have passed in the parameter.

Examples:

Battery level indicator icon, with different images to indicate the current battery level, as well as network strength indicator icon, we shall use the latter for our example.

The XML

It has  element as root.

Each Drawable level is defined in a nested element.

This resource can be referenced as the background drawable for an ImageView. The default image is the first in the list. It can then be prorammatically changed to one of the other levels with setImageLevel(int).

Example

Create an android project called LevelList.

Create  a drawable xml resource like so:

network_level.xml

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

<level-list xmlns:android="http://schemas.android.com/apk/res/android">

       <item android:maxLevel="0" android:drawable="@drawable/stat_sys_wifi_signal_0" />

       <item android:maxLevel="1" android:drawable="@drawable/stat_sys_wifi_signal_1" />

       <item android:maxLevel="2" android:drawable="@drawable/stat_sys_wifi_signal_2" />

       <item android:maxLevel="3" android:drawable="@drawable/stat_sys_wifi_signal_3" />

       <item android:maxLevel="4" android:drawable="@drawable/stat_sys_wifi_signal_4" />

</level-list>

I copied the drawables from the android 2.2 jar   res\drawable-mdpi folder, they may be named differently in the archive you have but should be having something like **wifi_signal_** in the name, check accordingly.

main.xml

create an ImageView to use the new drawable resource as a background and 5 buttons to switch the image level, like so:

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

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

       android:orientation="vertical"

       android:layout_width="fill_parent"

       android:layout_height="fill_parent">

      

       <TextView

             android:layout_width="fill_parent"

             android:layout_height="wrap_content"

             android:text="Network level indicator" />

            

       <ImageView

             android:id="@+id/network_level"

             android:layout_height="wrap_content"

             android:layout_width="wrap_content"

             android:src="@drawable/network_level" />

            

       <LinearLayout

             android:layout_height="wrap_content"

             android:layout_width="fill_parent"

             android:weightSum="5">

            

             <Button

                    android:layout_height="40dp"

                    android:layout_width="wrap_content"

                    android:text="0"

                    android:id="@+id/networklevel0"

                    android:layout_weight="1"

                    android:onClick="onClick" />

             <Button

                    android:layout_height="40dp"

                    android:layout_width="wrap_content"

                    android:id="@+id/networklevel1"

                    android:text="1"

                    android:layout_weight="1"

                    android:onClick="onClick" />

                   

             <Button

                    android:layout_height="40dp"

                    android:layout_width="wrap_content"

                    android:id="@+id/networklevel2"

                    android:text="2"

                    android:layout_weight="1"

                    android:onClick="onClick" />

                   

             <Button

                    android:layout_height="40dp"

                    android:layout_width="wrap_content"

                    android:id="@+id/networklevel3"

                    android:text="3"

                    android:layout_weight="1"

                    android:onClick="onClick" />

                   

             <Button

                    android:layout_height="40dp"

                    android:layout_width="wrap_content"

                    android:id="@+id/networklevel4"

                    android:text="4"

                    android:layout_weight="1"

                    android:onClick="onClick" />

       </LinearLayout>

</LinearLayout>

The buttons must have id’s since we shall have to access them programmatically. Notice how I have referenced an onClick from xml, there fore we have to create such a method in the activity and pass to it a view like so:

package com.simplejavan.level;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.widget.ImageView;

public class LevelListActivity extends Activity {

               ImageView networkLevel;

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        networkLevel= (ImageView) findViewById(R.id.network_level);

    }

    public void onClick(View v){

               int idd=v.getId();

               if(idd==R.id.networklevel0)

                              networkLevel.setImageLevel(0);

               if(idd==R.id.networklevel1)

                              networkLevel.setImageLevel(1);

               if(idd==R.id.networklevel2)

                              networkLevel.setImageLevel(2);

               if(idd==R.id.networklevel3)

                              networkLevel.setImageLevel(3);

               if(idd==R.id.networklevel4)

                              networkLevel.setImageLevel(4);

    }

}

Load the app and switch network level from the buttons.

This is it for the basics of LevelListDrawable, I will be adding any new ideas or new findings I get in subsequent blog posts. Thanks for reading.