android error java.lang.NoClassDefFoundError
<p>I have android app in market so I get this error but I don't know why.</p>

<pre><code>Exception class java.lang.NoClassDefFoundError
Source method MainActivity.onCreate()

java.lang.NoClassDefFoundError: android.app.DownloadManager
at com.example.viewpagerexample.MainActivity.onCreate(MainActivity.java:182)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1069)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2751)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2803)
at android.app.ActivityThread.access$2300(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2136)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:144)
at android.app.ActivityThread.main(ActivityThread.java:4937)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
at dalvik.system.NativeStart.main(Native Method)
</code></pre>
