有些列表信息需要手动去更新，此时比较常用的就是下拉刷新列表，在这里就使用下拉列表来刷新当前Wifi信息

目录结构

界面

关键代码

下拉列表类

package com.example.dropdownrefresh.ui;
 
import java.text.SimpleDateFormat;
import java.util.Date;
 
import com.example.dropdownrefresh.R;
 
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.LinearInterpolator;
import android.view.animation.RotateAnimation;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.TextView;
 
/**
 * 下拉列表类
 * @author Administrator
 *
 */
public class DropdownListView extends ListView implements OnScrollListener {
 
    private static final String TAG = listview;
 
    private final static int RELEASE_To_REFRESH = 0;
    private final static int PULL_To_REFRESH = 1;
    private final static int REFRESHING = 2;
    private final static int DONE = 3;
    private final static int LOADING = 4;
 
    // 实际的padding的距离与界面上偏移距离的比例
    private final static int RATIO = 3;
    private LayoutInflater inflater;
    private LinearLayout headView;
    private TextView tipsTextview;
    private TextView lastUpdatedTextView;
    private ImageView arrowImageView;
    private ProgressBar progressBar;
    private RotateAnimation animation;
    private RotateAnimation reverseAnimation;
 
    // 用于保证startY的值在一个完整的touch事件中只被记录一次
    private boolean isRecored;
    private int headContentWidth;
    private int headContentHeight;
    private int startY;
    private int firstItemIndex;
    private int state;
    private boolean isBack;
    private OnRefreshListener refreshListener;
    private boolean isRefreshable;
    public DropdownListView(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
        init(context);
    }
 
    public DropdownListView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }
 
    private void init(Context context) {
        setCacheColorHint(context.getResources().getColor(R.color.transparent));
        inflater = LayoutInflater.from(context);
 
        headView = (LinearLayout) inflater.inflate(R.layout.head, null);
 
        arrowImageView = (ImageView) headView
                .findViewById(R.id.head_arrowImageView);
        arrowImageView.setMinimumWidth(70);
        arrowImageView.setMinimumHeight(50);
        progressBar = (ProgressBar) headView
                .findViewById(R.id.head_progressBar);
        tipsTextview = (TextView) headView.findViewById(R.id.head_tipsTextView);
        lastUpdatedTextView = (TextView) headView
                .findViewById(R.id.head_lastUpdatedTextView);
 
        measureView(headView);
        headContentHeight = headView.getMeasuredHeight();
        headContentWidth = headView.getMeasuredWidth();
 
        headView.setPadding(0, -1 * headContentHeight, 0, 0);
        headView.invalidate();
 
        Log.v(size, width: + headContentWidth +  height:
                + headContentHeight);
 
        addHeaderView(headView, null, false);
        setOnScrollListener(this);
 
        animation = new RotateAnimation(0, -180,
                RotateAnimation.RELATIVE_TO_SELF, 0.5f,
                RotateAnimation.RELATIVE_TO_SELF, 0.5f);
        animation.setInterpolator(new LinearInterpolator());
        animation.setDuration(250);
        animation.setFillAfter(true);
 
        reverseAnimation = new RotateAnimation(-180, 0,
                RotateAnimation.RELATIVE_TO_SELF, 0.5f,
                RotateAnimation.RELATIVE_TO_SELF, 0.5f);
        reverseAnimation.setInterpolator(new LinearInterpolator());
        reverseAnimation.setDuration(200);
        reverseAnimation.setFillAfter(true);
 
        state = DONE;
        isRefreshable = false;
    }
 
    @Override
    public void onScroll(AbsListView arg0, int firstVisiableItem, int arg2,
            int arg3) {
        // TODO Auto-generated method stub
        firstItemIndex = firstVisiableItem;
    }
 
    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        // TODO Auto-generated method stub
 
    }
 
    public boolean onTouchEvent(MotionEvent event) {
 
        if (isRefreshable) {
            switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                if (firstItemIndex == 0 && !isRecored) {
                    isRecored = true;
                    startY = (int) event.getY();
                    Log.v(TAG, 在down时候记录当前位置‘);
                }
                break;
 
            case MotionEvent.ACTION_UP:
 
                if (state != REFRESHING && state != LOADING) {
                    if (state == DONE) {
                        // 什么都不做
                    }
                    if (state == PULL_To_REFRESH) {
                        state = DONE;
                        changeHeaderViewByState();
 
                        Log.v(TAG, 由下拉刷新状态，到done状态);
                    }
                    if (state == RELEASE_To_REFRESH) {
                        state = REFRESHING;
                        changeHeaderViewByState();
                        onRefresh();
 
                        Log.v(TAG, 由松开刷新状态，到done状态);
                    }
                }
 
                isRecored = false;
                isBack = false;
 
                break;
 
            case MotionEvent.ACTION_MOVE:
                int tempY = (int) event.getY();
 
                if (!isRecored && firstItemIndex == 0) {
                    Log.v(TAG, 在move时候记录下位置);
                    isRecored = true;
                    startY = tempY;
                }
 
                if (state != REFRESHING && isRecored && state != LOADING) {
 
                    // 保证在设置padding的过程中，当前的位置一直是在head，否则如果当列表超出屏幕的话，当在上推的时候，列表会同时进行滚动
 
                    // 可以松手去刷新了
                    if (state == RELEASE_To_REFRESH) {
 
                        setSelection(0);
 
                        // 往上推了，推到了屏幕足够掩盖head的程度，但是还没有推到全部掩盖的地步
                        if (((tempY - startY) / RATIO < headContentHeight)
                                && (tempY - startY) > 0) {
                            state = PULL_To_REFRESH;
                            changeHeaderViewByState();
 
                            Log.v(TAG, 由松开刷新状态转变到下拉刷新状态);
                        }
                        // 一下子推到顶了
                        else if (tempY - startY <= 0) {
                            state = DONE;
                            changeHeaderViewByState();
 
                            Log.v(TAG, 由松开刷新状态转变到done状态);
                        }
                        // 往下拉了，或者还没有上推到屏幕顶部掩盖head的地步
                        else {
                            // 不用进行特别的操作，只用更新paddingTop的值就行了
                        }
                    }
                    // 还没有到达显示松开刷新的时候,DONE或者是PULL_To_REFRESH状态
                    if (state == PULL_To_REFRESH) {
 
                        setSelection(0);
 
                        // 下拉到可以进入RELEASE_TO_REFRESH的状态
                        if ((tempY - startY) / RATIO >= headContentHeight) {
                            state = RELEASE_To_REFRESH;
                            isBack = true;
                            changeHeaderViewByState();
 
                            Log.v(TAG, 由done或者下拉刷新状态转变到松开刷新);
                        }
                        // 上推到顶了
                        else if (tempY - startY <= 0) {
                            state = DONE;
                            changeHeaderViewByState();
 
                            Log.v(TAG, 由DOne或者下拉刷新状态转变到done状态);
                        }
                    }
 
                    // done状态下
                    if (state == DONE) {
                        if (tempY - startY > 0) {
                            state = PULL_To_REFRESH;
                            changeHeaderViewByState();
                        }
                    }
 
                    // 更新headView的size
                    if (state == PULL_To_REFRESH) {
                        headView.setPadding(0, -1 * headContentHeight
                                + (tempY - startY) / RATIO, 0, 0);
 
                    }
 
                    // 更新headView的paddingTop
                    if (state == RELEASE_To_REFRESH) {
                        headView.setPadding(0, (tempY - startY) / RATIO
                                - headContentHeight, 0, 0);
                    }
 
                }
 
                break;
            }
        }
 
        return super.onTouchEvent(event);
    }
 
    /**
     * 当状态改变时候，调用该方法，以更新界面
     */
    private void changeHeaderViewByState() {
        switch (state) {
        case RELEASE_To_REFRESH:
            arrowImageView.setVisibility(View.VISIBLE);
            progressBar.setVisibility(View.GONE);
            tipsTextview.setVisibility(View.VISIBLE);
            lastUpdatedTextView.setVisibility(View.VISIBLE);
 
            arrowImageView.clearAnimation();
            arrowImageView.startAnimation(animation);
 
            tipsTextview.setText(松开刷新);
 
            Log.v(TAG, 当前状态，松开刷新);
            break;
        case PULL_To_REFRESH:
            progressBar.setVisibility(View.GONE);
            tipsTextview.setVisibility(View.VISIBLE);
            lastUpdatedTextView.setVisibility(View.VISIBLE);
            arrowImageView.clearAnimation();
            arrowImageView.setVisibility(View.VISIBLE);
            // 是由RELEASE_To_REFRESH状态转变来的
            if (isBack) {
                isBack = false;
                arrowImageView.clearAnimation();
                arrowImageView.startAnimation(reverseAnimation);
 
                tipsTextview.setText(下拉刷新);
            } else {
                tipsTextview.setText(下拉刷新);
            }
            Log.v(TAG, 当前状态，下拉刷新);
            break;
 
        case REFRESHING:
 
            headView.setPadding(0, 0, 0, 0);
 
            progressBar.setVisibility(View.VISIBLE);
            arrowImageView.clearAnimation();
            arrowImageView.setVisibility(View.GONE);
            tipsTextview.setText(正在刷新...);
            lastUpdatedTextView.setVisibility(View.VISIBLE);
 
            Log.v(TAG, 当前状态,正在刷新...);
            break;
        case DONE:
            headView.setPadding(0, -1 * headContentHeight, 0, 0);
 
            progressBar.setVisibility(View.GONE);
            arrowImageView.clearAnimation();
            arrowImageView.setImageResource(R.drawable.arrow);
            tipsTextview.setText(下拉刷新);
            lastUpdatedTextView.setVisibility(View.VISIBLE);
 
            Log.v(TAG, 当前状态，done);
            break;
        }
    }
 
    public void setonRefreshListener(OnRefreshListener refreshListener) {
        this.refreshListener = refreshListener;
        isRefreshable = true;
    }
 
    public interface OnRefreshListener {
        public void onRefresh();
    }
 
    public void onRefreshComplete() {
        state = DONE;
        SimpleDateFormat sdf = new SimpleDateFormat(yyyy-MM-dd HH:mm:ss);
        lastUpdatedTextView.setText(最近更新: + sdf.format(new Date()));
        changeHeaderViewByState();
    }
 
    private void onRefresh() {
        if (refreshListener != null) {
            refreshListener.onRefresh();
        }
    }
 
    /**
     * 此方法直接照搬自网络上的一个下拉刷新的demo，此处是“估计”headView的width以及height
     * @param child
     */
    private void measureView(View child) {
        ViewGroup.LayoutParams p = child.getLayoutParams();
        if (p == null) {
            p = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
                    ViewGroup.LayoutParams.WRAP_CONTENT);
        }
        int childWidthSpec = ViewGroup.getChildMeasureSpec(0, 0 + 0, p.width);
        int lpHeight = p.height;
        int childHeightSpec;
        if (lpHeight > 0) {
            childHeightSpec = MeasureSpec.makeMeasureSpec(lpHeight,
                    MeasureSpec.EXACTLY);
        } else {
            childHeightSpec = MeasureSpec.makeMeasureSpec(0,
                    MeasureSpec.UNSPECIFIED);
        }
        child.measure(childWidthSpec, childHeightSpec);
    }
 
    public void setAdapter(BaseAdapter adapter) {
        SimpleDateFormat sdf = new SimpleDateFormat(yyyy-MM-dd HH:mm:ss);
        lastUpdatedTextView.setText(最近更新: + sdf.format(new Date()));
        super.setAdapter(adapter);
    }
}

main.xml

<!--?xml version=1.0 encoding=utf-8?-->
 
<!-- ListView的头部 -->
 
<linearlayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="wrap_content">
 
    <!-- 内容 -->
 
    <relativelayout android:id="@+id/head_contentLayout" android:layout_width="match_parent" android:layout_height="wrap_content" android:paddingleft="30dp">
 
        <!-- 箭头图像、进度条 -->
 
        <framelayout android:layout_alignparentleft="true" android:layout_centervertical="true" android:layout_height="wrap_content" android:layout_width="wrap_content">
 
            <!-- 箭头 -->
 
            <imageview android:id="@+id/head_arrowImageView" android:layout_width="wrap_content" android:layout_height="wrap_content" android:src="@drawable/arrow" android:layout_gravity="center" android:contentdescription="@null">
 
            <!-- 进度条 -->
 
            <progressbar android:id="@+id/head_progressBar" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="center" android:visibility="gone">
        </progressbar></imageview></framelayout>
 
        <!-- 提示、最近更新 -->
 
        <linearlayout android:layout_width="wrap_content" android:layout_height="wrap_content" android:orientation="vertical" android:layout_centerhorizontal="true" android:gravity="center_horizontal">
 
            <!-- 提示 -->
 
            <textview android:id="@+id/head_tipsTextView" android:layout_width="wrap_content" android:layout_height="wrap_content" android:textsize="20sp" android:textcolor="@color/white" android:text="下拉刷新">
 
            <!-- 最近更新 -->
 
            <textview android:id="@+id/head_lastUpdatedTextView" android:layout_width="wrap_content" android:layout_height="wrap_content" android:textsize="12sp" android:textcolor="@color/gold" android:text="上次更新">
        </textview></textview></linearlayout>
    </relativelayout>
 
</linearlayout>

下拉列表松开后需要扫描Wifi，再刷新列表

package com.example.dropdownrefresh;
 
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
 
import android.app.Activity;
import android.net.wifi.ScanResult;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.LinearLayout;
import android.widget.TextView;
 
import com.example.dropdownrefresh.ui.DropdownListView;
import com.example.dropdownrefresh.ui.DropdownListView.OnRefreshListener;
import com.example.dropdownrefresh.utils.WifiAdmin;
 
/**
 * 使用下拉刷新搜索wifi
 * @author Administrator
 *
 */
public class MainActivity extends Activity {
 
    WifiAdmin wifiAdmin = null;
    private ArrayList<hashmap<string, string="">> list;
    private BaseAdapter adapter;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        wifiAdmin = new WifiAdmin(this);
        list = new ArrayList<hashmap<string, string="">>();
        RefreshList();
 
        final DropdownListView listView = (DropdownListView) findViewById(R.id.listView);
        adapter = new BaseAdapter() {
            public View getView(int position, View convertView, ViewGroup parent) {
                LinearLayout layout = new LinearLayout(getApplicationContext());
                layout.setOrientation(LinearLayout.VERTICAL);  //垂直布局
                HashMap<string, string=""> map = list.get(position);
                TextView txtName = new TextView(getApplicationContext());
                TextView txtSignal = new TextView(getApplicationContext());
                txtName.setText(map.get(wifi_name));
                txtSignal.setText(map.get(wifi_signal));
                layout.addView(txtName);
                layout.addView(txtSignal);
                return layout;
            }
 
            public long getItemId(int position) {
                return 0;
            }
 
            public Object getItem(int position) {
                return null;
            }
 
            public int getCount() {
                return list.size();
            }
        };
        listView.setAdapter(adapter);
 
        listView.setonRefreshListener(new OnRefreshListener() {
            public void onRefresh() {
                new AsyncTask<void, void="">() {
                    protected Void doInBackground(Void... params) {
                        try {
                            Thread.sleep(1000);
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                        list.clear();
                        RefreshList();
                        return null;
                    }
 
                    @Override
                    protected void onPostExecute(Void result) {
                        adapter.notifyDataSetChanged();
                        listView.onRefreshComplete();
                    }
 
                }.execute(null, null, null);
            }
        });
    }
     
    private void RefreshList(){
        wifiAdmin.startScan(); // 扫描wifi热点，前提是wifi已经打开
        List<scanresult> wifiList = wifiAdmin.getWifiList();
        for (int index = 0; index < wifiList.size(); index++) {
            HashMap<string, string=""> map = new HashMap<string, string="">();
            map.put(wifi_name, (wifiList.get(index)).SSID);
            map.put(wifi_signal, signal: 
                    + (-(wifiList.get(index)).level) + %);
            list.add(map);
        }
    }
}