<AutoCompleteTextView
  android:id="@+id/mp002_top_place_input"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:completionThreshold="1"
  android:layout_marginTop="5dp" >
</AutoCompleteTextView>

AutoCompleteTextView mPlace = (AutoCompleteTextView)findViewById(R.id.mp002_top_place_input);
ArrayList<String> result = new ArrayList<String>();
result.add("1111111");
result.add("1222222");
mPlace.setAdapter(new ArrayAdapter<String>(
   MP002TopActivity.this,
   android.R.layout.simple_dropdown_item_1line,
   result)
);

public class MyAutoCompleteTextView extends AutoCompleteTextView{
 public MyAutoCompleteTextView(Context context) {
  super(context);
 }
 public MyAutoCompleteTextView(Context context, AttributeSet attrs) {
  super(context, attrs);
 }
 public MyAutoCompleteTextView(Context context, AttributeSet attrs, int defStyle) {
  super(context, attrs, defStyle);
 }
 @Override
 public boolean enoughToFilter() {
  return true;
 }
 @Override
 protected void onFocusChanged(boolean focused, int direction, Rect previouslyFocusedRect) {
  super.onFocusChanged(focused, direction, previouslyFocusedRect);
  performFiltering(getText(), KeyEvent.KEYCODE_UNKNOWN);
 }
}

public class EmailAutoCompleteTextView extends AutoCompleteTextView {
  private static final String TAG = "EmailAutoCompleteTextView";

  private String[] emailSufixs = new String[] { "@163.com",
    "@gmail.com", "@hotmail.com" };

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

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

  public EmailAutoCompleteTextView(Context context, AttributeSet attrs,
      int defStyle) {
    super(context, attrs, defStyle);
    init(context);
  }
  
  public void setAdapterString(String[] es) {
    if(es != null && es.length > 0)
      this.emailSufixs = es;
  }
  
  private void init(final Context context) {
    //adapter中使用默认的emailSufixs中的数据，可以通过setAdapterString来更改
    this.setAdapter(new EmailAutoCompleteAdapter(context, R.layout.auto_complete_item, emailSufixs));
    
    //使得在输入1个字符之后便开启自动完成
    this.setThreshold(1);

    this.setOnFocusChangeListener(new OnFocusChangeListener() {
      
      @Override
      public void onFocusChange(View v, boolean hasFocus) {
        if(hasFocus) {
          String text = EmailAutoCompleteTextView.this.getText().toString();
          //当该文本域重新获得焦点后，重启自动完成
          if(!"".equals(text))
            performFiltering(text, 0);
        } else {
          //当文本域丢失焦点后，检查输入email地址的格式
          EmailAutoCompleteTextView ev = (EmailAutoCompleteTextView) v;
          String text = ev.getText().toString();
          //这里正则写的有点粗暴:)
          if(text != null && text.matches("^[a-zA-Z0-9_]+@[a-zA-Z0-9]+\\.[a-zA-Z0-9]+$")) {
            Toast to = new Toast(context);
            ImageView i = new ImageView(context);
            i.setBackgroundResource(R.drawable.img_success);
            to.setView(i);
            to.show();
          } else {
            Toast toast = Toast.makeText(context, "邮件地址格式不正确", Toast.LENGTH_SHORT);
            toast.setGravity(Gravity.TOP, 0, 50);
            toast.show();
          }
        }
      }
    });
  }
  
  

  @Override
  protected void replaceText(CharSequence text) {
    //当我们在下拉框中选择一项时，android会默认使用AutoCompleteTextView中Adapter里的文本来填充文本域
    //因为这里Adapter中只是存了常用email的后缀
    //因此要重新replace逻辑，将用户输入的部分与后缀合并
    Log.i(TAG + " replaceText", text.toString());
    String t = this.getText().toString();
    int index = t.indexOf("@");
    if(index != -1)
      t = t.substring(0, index);
    super.replaceText(t + text);
  }

  @Override
  protected void performFiltering(CharSequence text, int keyCode) {
    //该方法会在用户输入文本之后调用，将已输入的文本与adapter中的数据对比，若它匹配
    //adapter中数据的前半部分，那么adapter中的这条数据将会在下拉框中出现
    Log.i(TAG + " performFiltering", text.toString() + "  " + keyCode);
    String t = text.toString();
    
    //因为用户输入邮箱时，都是以字母，数字开始，而我们的adapter中只会提供以类似于"@163.com"
    //的邮箱后缀，因此在调用super.performFiltering时，传入的一定是以"@"开头的字符串
    int index = t.indexOf("@");
    if(index == -1) {
      if(t.matches("^[a-zA-Z0-9_]+$")) {
        super.performFiltering("@", keyCode);
      }
      else
        this.dismissDropDown();//当用户中途输入非法字符时，关闭下拉提示框
    } else {
      super.performFiltering(t.substring(index), keyCode);
    }
  }

  
  private class EmailAutoCompleteAdapter extends ArrayAdapter<String> {

    public EmailAutoCompleteAdapter(Context context, int textViewResourceId, String[] email_s) {
      super(context, textViewResourceId, email_s);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
      Log.i(TAG, "in GetView");
      View v = convertView;
      if (v == null)
        v = LayoutInflater.from(getContext()).inflate(
            R.layout.auto_complete_item, null);
      TextView tv = (TextView) v.findViewById(R.id.tv);
      
      String t = EmailAutoCompleteTextView.this.getText().toString();
      int index = t.indexOf("@");
      if(index != -1)
        t = t.substring(0, index);
      //将用户输入的文本与adapter中的email后缀拼接后，在下拉框中显示
      tv.setText(t + getItem(position));
      Log.i(TAG, tv.getText().toString());
      return v;
    }
  }
}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical" >

  <com.example.testautocompletetextview.EmailAutoCompleteTextView
    android:id="@+id/act"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="Email Address"
    android:textColor="@color/black" />

  <!-- 用于测试移开焦点 -->
  <EditText
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginTop="20dp"
    android:drawableLeft="@drawable/amount_selected" />

</LinearLayout>
下拉提示框中每一项（TextView）的xml：

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
  android:id="@+id/tv"
  android:padding="8dp"
  android:layout_width="match_parent"
  android:layout_height="wrap_content" />