about MultiAutoCompleteTextView

 public class testMultiAutoCompleteTextView extends ListActivity  {
/** Called when the activity is first created. */
private MultiAutoCompleteTextView searchEdit;
 Button   okButton;
private ArrayAdapter<String> adapter = null;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    adapter = new ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_1, mStrings);

   setListAdapter(adapter);

    searchEdit = (MultiAutoCompleteTextView) findViewById(R.id.search_box);

    searchEdit.addTextChangedListener(filterTextWatcher);

    searchEdit.setTokenizer(new SpaceTokenizer());

    searchEdit.se开发者_如何学运维tAdapter(adapter);

    searchEdit.setOnClickListener(new OnClickListener() {

        public void onClick(View v) {
            String t = ((TextView) v).getText().toString();
            String f = searchEdit.getText().toString();

            int s = searchEdit.getSelectionStart();
            int i = s;

            while (i > 0 && f.charAt(i - 1) != ' ') {
                i--;
            }

            adapter.getFilter().filter(t.substring(i, s));
        }
    });

    okButton = (Button) findViewById(R.id.ok);
    okButton.setOnClickListener(new OnClickListener() {

        public void onClick(View v) {
            Bundle stats = new Bundle();
            stats.putString("ConversationName", searchEdit.getText()
                    .toString());

            Intent i = new Intent();
            i.putExtras(stats);
            setResult(RESULT_OK, i);
            finish();
        }
    });

    searchEdit.setOnKeyListener(new OnKeyListener() {

        public boolean onKey(View v, int keyCode, KeyEvent event) {
            if (keyCode == KeyEvent.KEYCODE_DPAD_LEFT
                    || keyCode == KeyEvent.KEYCODE_DPAD_RIGHT
                    || keyCode == KeyEvent.KEYCODE_DPAD_UP
                    || keyCode == KeyEvent.KEYCODE_DPAD_DOWN) {

                String t = ((TextView) v).getText().toString();
                String f = searchEdit.getText().toString();

                int s = searchEdit.getSelectionStart();
                int i = s;

                while (i > 0 && f.charAt(i - 1) != ' ') {
                    i--;
                }

                adapter.getFilter().filter(t.substring(i, s));

                return false;
            }

            return false;
        }
    });

    getListView().setOnItemClickListener(
            new ListView.OnItemClickListener() {
                public void onItemClick(AdapterView<?> parent, View view,
                        int position, long id) {

                    String t = adapter.getItem(position);
                    String f = searchEdit.getText().toString();

                    int s = searchEdit.getSelectionStart();
                    int i = s;

                    while (i > 0 && f.charAt(i - 1) != ' ') {
                        i--;
                    }

                    searchEdit.getText().insert(s, t.substring(s - i));
                }
            });
}


    @Override
protected void onDestroy() {
    super.onDestroy();
    searchEdit.removeTextChangedListener(filterTextWatcher);
}


private TextWatcher filterTextWatcher = new TextWatcher() {

    public void afterTextChanged(Editable s) {
        okButton.setEnabled(searchEdit.getText().toString().trim()
                .length() > 0);
    }

    public void beforeTextChanged(CharSequence s, int start, int count,
            int after) {
    }

    public void onTextChanged(CharSequence s, int start, int before,
            int count) {
        adapter.getFilter().filter(s);
    }

};



public class SpaceTokenizer implements Tokenizer {

public int findTokenStart(CharSequence text, int cursor) {
    int i = cursor;

    while (i > 0 && text.charAt(i - 1) != ' ') {
        i--;
    }
    while (i < cursor && text.charAt(i) == ' ') {
        i++;
    }

    return i;
}

public int findTokenEnd(CharSequence text, int cursor) {
    int i = cursor;
    int len = text.length();

    while (i < len) {
        if (text.charAt(i) == ' ') {
            return i;
        } else {
            i++;
        }
    }

    return len;
}

public CharSequence terminateToken(CharSequence text) {
    int i = text.length();

    while (i > 0 && text.charAt(i - 1) == ' ') {
        i--;
    }

    if (i > 0 && text.charAt(i - 1) == ' ') {
        return text;
    } else {
        if (text instanceof Spanned) {
            SpannableString sp = new SpannableString(text + " ");
            TextUtils.copySpansFrom((Spanned) text, 0, text.length(),
                    Object.class, sp, 0);
            return sp;
        } else {
            return text + " ";
        }
    }
}
}
 private String[] mStrings = {

            "Vacherin-Fribourgeois", "Valencay", "Vasterbottenost", "Venaco", "Vendomois",
            "Vieux Corse", "Vignotte", "Vulscombe", "Waimata Farmhouse Blue",
            "Washed Rind Cheese (Australian)", "Waterloo", "Weichkaese", "Wellington",
            "Wensleydale", "White Stilton", "Whitestone Farmhouse", "Wigmore", "Woodside Cabecou",
            "Xanadu", "Xynotyro", "Yarg Cornish", "Yarra Valley Pyramid", "Yorkshire Blue",
            "Zamorano", "Zanetti Grana Padano", "Zanetti Parmigiano Reggiano"};

} my xml:

   <?xml version="1.0" encoding="utf-8"?>
   <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
      android:layout_width="fill_parent" android:layout_height="fill_parent"
       android:orientation="vertical"
       android:drawingCacheQuality="high">

   <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
       android:layout_width="fill_parent" android:layout_height="wrap_content"
       android:orientation="horizontal">


<MultiAutoCompleteTextView
    android:layout_marginLeft="1dip"
    android:layout_marginTop="1dip"
    android:layout_height="wrap_content" 
    android:layout_weight="1"
    android:layout_width="fill_parent"
    android:dropDownHeight="0px" 
    android:hint="@string/To" 
    android:id="@+id/search_box"
    ></MultiAutoCompleteTextView>



<Button android:layout_width="wrap_content"
    android:layout_height="wrap_content" 
    android:text="Ok"
    android:id="@+id/ok"
    android:enabled="false"
    />  


  </LinearLayout>     
  <ListView android:id="@android:id/list" android:layout_width="fill_parent"
    android:layout_height="fill_parent" android:layout_weight="1" />

    </LinearLayout>

it give me ERROR/AndroidRuntime(423): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.test.testMultiAutoCompleteTextView/com.test.testMultiAutoCompleteTextView.testMultiAutoCompleteTextView}: java.lang.NullPointerException

at onCreate method before to call

adapter = new ArrayAdapter<String>(this,
        android.R.layout.simple_list_item_1, mStrings);

you have to set you layout

setContentView(R.layout.you_xml_file_name);