/**
     * @see android.widget.ListAdapter#getCount()
     */
    public int getCount() {
        if (mDataValid && mCursor != null) {
            return mCursor.getCount();
        } else {
            return 0;
        }
    }
   
    /**
     * @see android.widget.ListAdapter#getItem(int)
     */
    public Object getItem( int position) {
        if (mDataValid && mCursor != null) {
            mCursor.moveToPosition(position);
            return mCursor;
        } else {
            return null;
        }
    }

    /**
     * @see android.widget.ListAdapter#getItemId(int)
     */
    public long getItemId( int position) {
        if (mDataValid && mCursor != null) {
            if ( mCursor.moveToPosition(position)) {
                return mCursor.getLong( mRowIDColumn);
            } else {
                return 0;
            }
        } else {
            return 0;
        }
    }

    /**
     * @see android.widget.ListAdapter# getView(int, View, ViewGroup)
     */
    public View getView( int position, View convertView, ViewGroup parent) {
        if (!mDataValid) {
            throw new IllegalStateException( "this should only be called when the cursor is valid");
        }
        if (!mCursor.moveToPosition(position)) {
            throw new IllegalStateException( "couldn't move cursor to position " + position);
        }
        View v;
        if (convertView == null) {
            v = newView( mContext, mCursor, parent);
        } else {
            v = convertView;
        }
        bindView(v, mContext, mCursor);
        return v;
    }

 /**
     * Makes a new view to hold the data pointed to by cursor.
     * @param context Interface to application's global information
     * @param cursor The cursor from which to get the data. The cursor is already
     * moved to the correct position.
     * @param parent The parent to which the new view is attached to
     * @return the newly created view.
     */
    public abstract View newView (Context context, Cursor cursor, ViewGroup parent);

       /**
     * Bind an existing view to the data pointed to by cursor
     * @param view Existing view, returned earlier by newView
     * @param context Interface to application's global information
     * @param cursor The cursor from which to get the data. The cursor is already
     * moved to the correct position.
     */
    public abstract void bindView(View view, Context context, Cursor cursor);

/**
     * Change the underlying cursor to a new cursor. If there is an existing cursor it will be
     * closed.
     *
     * @param cursor The new cursor to be used
     */
    public void changeCursor (Cursor cursor) {
        Cursor old = swapCursor(cursor);
        if (old != null) {
            old.close();
        }
    }
 swapCursor(cusor)的源码如下：

/**
     * Swap in a new Cursor, returning the old Cursor.  Unlike
     * {@link #changeCursor(Cursor)}, the returned old Cursor is <em>not</em>
     * closed.
     *
     * @param newCursor The new cursor to be used.
     * @return Returns the previously set Cursor, or null if there wasa not one.
     * If the given new Cursor is the same instance is the previously set
     * Cursor, null is also returned.
     */
    public Cursor swapCursor (Cursor newCursor) {
        if (newCursor == mCursor) {
            return null;
        }
        Cursor oldCursor = mCursor;
        if (oldCursor != null) {
            if ( mChangeObserver != null) oldCursor.unregisterContentObserver(mChangeObserver );
            if ( mDataSetObserver != null) oldCursor.unregisterDataSetObserver(mDataSetObserver );
        }
        mCursor = newCursor;
        if (newCursor != null) {
            if ( mChangeObserver != null) newCursor.registerContentObserver(mChangeObserver );
            if ( mDataSetObserver != null) newCursor.registerDataSetObserver(mDataSetObserver );
            mRowIDColumn = newCursor.getColumnIndexOrThrow("_id" );
            mDataValid = true;
            // notify the observers about the new cursor
            notifyDataSetChanged();
        } else {
            mRowIDColumn = -1;
            mDataValid = false;
            // notify the observers about the lack of a data set
            notifyDataSetInvalidated();
        }
        return oldCursor;
    }

private void setClickListener() {
           
            btn_save.setOnClickListener( new OnClickListener() {
                
                 public void onClick(View v) {
                     
                      userName=et_name.getText().toString();
                    userPhoneNumber=et_phonenumber .getText().toString();
                   
                    if( userName.equals( "")){
                     Toast. makeText(MainActivity.this, "用户名不能为空!",0).show();
                      return;
                    }
                    if( userPhoneNumber.equals( "")){
                     Toast. makeText(MainActivity.this,"电话不能为空", 0).show();
                      return;
                    }
                   
                    ContentValues contentValues= new ContentValues();
                    contentValues.put(PersonInfo. NAME, userName);
                    contentValues.put(PersonInfo.PHONENUMBER ,userPhoneNumber );
                    //把EditText中的文本插入数据库
                    dataBase.insert(PersonInfo. PERSON_INFO_TABLE, null,contentValues);
                    //根据 _id 降序插叙数据库保证最后插入的在最上面
                    Cursor myCursor          = dataBase.query(PersonInfo. PERSON_INFO_TABLE, null, null, null, null, null, orderBy);
                    //Cursor改变调用chanageCursor()方法
                    myCursorAdapter.changeCursor(myCursor);
                }
           });
     }