Exercise: Change background color, by SeekBar

In this exercise, the background color is changed, controlled by SeekBar.

A SeekBar is an extension of ProgressBar that adds a draggable thumb. The user can touch the thumb and drag left or right to set the current progress level or use the arrow keys.

When SeekBarChange, the onProgressChanged() of OnSeekBarChangeListener will be called, and the background of the screen(LinearLayout) will be updated according to the value (SeekBar.getProgress()).

Create a Android Application, SeekColor, with three SeekBar for Red, Green and Blue setting.

main.xml

<?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"
android:id="@+id/myScreen"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello"
/>
<SeekBar
android:id="@+id/mySeekingBar_R"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:max="255"
    android:progress="0"/>
<SeekBar
android:id="@+id/mySeekingBar_G"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:max="255"
    android:progress="0"/>
<SeekBar
android:id="@+id/mySeekingBar_B"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:max="255"
    android:progress="0"/>
</LinearLayout>

SeekColorActivity.java

package com.exercise.seekcolor;

import android.app.Activity;
import android.os.Bundle;
import android.widget.LinearLayout;
import android.widget.SeekBar;

public class SeekColorActivity extends Activity {

private int seekR, seekG, seekB;
SeekBar redSeekBar, greenSeekBar, blueSeekBar;
LinearLayout mScreen;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mScreen = (LinearLayout) findViewById(R.id.myScreen);
    redSeekBar = (SeekBar) findViewById(R.id.mySeekingBar_R);
    greenSeekBar = (SeekBar) findViewById(R.id.mySeekingBar_G);
    blueSeekBar = (SeekBar) findViewById(R.id.mySeekingBar_B);
    updateBackground();

    redSeekBar.setOnSeekBarChangeListener(seekBarChangeListener);
    greenSeekBar.setOnSeekBarChangeListener(seekBarChangeListener);
    blueSeekBar.setOnSeekBarChangeListener(seekBarChangeListener);

}

private SeekBar.OnSeekBarChangeListener seekBarChangeListener
= new SeekBar.OnSeekBarChangeListener()
{

@Override
public void onProgressChanged(SeekBar seekBar, int progress,
  boolean fromUser) {
// TODO Auto-generated method stub
 updateBackground();
}
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
// TODO Auto-generated method stub
}

@Override
public void onStopTrackingTouch(SeekBar seekBar) {
// TODO Auto-generated method stub
}
};

private void updateBackground()
{
 seekR = redSeekBar.getProgress();
 seekG = greenSeekBar.getProgress();
 seekB = blueSeekBar.getProgress();
 mScreen.setBackgroundColor(
  0xff000000
  + seekR * 0x10000
  + seekG * 0x100
  + seekB
  );
}
}