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

<animation-list xmlns:android="http://schemas.android.com/apk/res/android"
  android:oneshot="false">
  <item android:drawable="@drawable/s1" android:duration="300" />
  <item android:drawable="@drawable/s2" android:duration="300" />
  <item android:drawable="@drawable/s3" android:duration="300" />
  <item android:drawable="@drawable/s4" android:duration="300" />
  <item android:drawable="@drawable/s5" android:duration="300" />
</animation-list>

public class SnailBar extends SeekBar {

  public SnailBar(Context context) {
    super(context);
    init();
  }

  public SnailBar(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  public SnailBar(Context context, AttributeSet attrs,
          int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init();
  }

  private void init() {
      setMax(100);//设置最大进度
    setThumbOffset(dip2px(getContext(), 20));
    setBackgroundResource(R.drawable.sbg);//设置背景
    int padding = dip2px(getContext(),(float)20);
    setPadding(padding, padding, padding, padding);//设置内边距
    setProgressDrawable(getResources().
        getDrawable(R.drawable.snailbar_define_style));
  }

  @Override
  protected void onAttachedToWindow() {
    super.onAttachedToWindow();
    AnimationDrawable drawable =
        (AnimationDrawable)this.getThumb();
    drawable.start();
  }

  public int dip2px(Context context, float dpValue) {
    final float scale = context.getResources()
        .getDisplayMetrics().density;
    return (int) (dpValue * scale + 0.5f);
  }
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:background="#deeaeb">

  <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical">

    <TextView
      android:id="@+id/seekbar_percent"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginTop="10dp"
      android:text="SnailBar"
      android:textSize="24sp"
      android:textStyle="bold" />

    <TextView
      android:id="@+id/seekbar_status"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="snailbar status"
      android:textSize="14sp" />

    <ad.pintextview.SnailBar
      android:id="@+id/seekBar"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_marginTop="30dp"
      android:thumb="@drawable/snailanim"/>

  </LinearLayout>
</RelativeLayout>

public class MainActivity extends AppCompatActivity {
  private SeekBar seekBar;
  private TextView seekbar_status;
  int len = 0;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    seekBar = (SeekBar) findViewById(R.id.seekBar);
    seekBar.setMax(100);
    seekbar_status = (TextView) findViewById(R.id.seekbar_status);
    handler.sendEmptyMessage(1);

  }

  private Handler handler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
      switch (msg.what) {
        case 1:
          handleHandler();
          break;
      }
    }
  };

  private void handleHandler() {
    if (seekBar.getProgress() < 100) {
      if (seekBar.getProgress() < 20) {
        len += 2;
        handler.sendEmptyMessageDelayed(1, 500);
        seekbar_status.setText("Normal download speed.");
      } else if (seekBar.getProgress() > 21
          && seekBar.getProgress() < 26) {
        len += 1;
        handler.sendEmptyMessageDelayed(1, 1000);
        seekbar_status.
            setText("Sundden speed down or disconnet...");
      } else {
        len += 2;
        handler.sendEmptyMessageDelayed(1, 50);
        seekbar_status.setText("Sundden speed up.");
      }
      seekBar.setProgress(len);
    }
  }
}

seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
  @Override
  public void onProgressChanged(SeekBar seekBar, int i, boolean b) {
    if(seekBar.getProgress()==100){
      AnimationDrawable drawable =
          (AnimationDrawable)seekBar.getThumb();
      drawable.stop();
    }
  }

  @Override
  public void onStartTrackingTouch(SeekBar seekBar) {

  }

  @Override
  public void onStopTrackingTouch(SeekBar seekBar) {

  }
});