Android中在GridView网格视图上实现item拖拽交换的方法

<?xml version="1.0" encoding="utf-8"?> 
<GridView 
 xmlns:android="http://schemas.android.com/apk/res/android" 
 android:id="@+id/gridview" 
 android:layout_width="fill_parent" 
 android:layout_height="fill_parent" 
 android:columnWidth="90dp" 
 android:numColumns="auto_fit" 
 android:horizontalSpacing="10dp" 
 android:verticalSpacing="10dp" 
 android:stretchMode="columnWidth" 
 android:gravity="center"> 
</GridView> 

public class HelloGridView extends Activity { 
  /** Called when the activity is first created. */ 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    GridView gridView=(GridView)findViewById(R.id.gridview); 
    gridView.setAdapter(new ImageAdapter(this)); 
    //单击GridView元素的响应 
    gridView.setOnItemClickListener(new OnItemClickListener() { 
 
      @Override 
      public void onItemClick(AdapterView<?> parent, View view, 
          int position, long id) { 
        //弹出单击的GridView元素的位置 
        Toast.makeText(HelloGridView.this,mThumbIds[position], Toast.LENGTH_SHORT).show(); 
      } 
    }); 
  } 
  private class ImageAdapter extends BaseAdapter{ 
    private Context mContext; 
 
    public ImageAdapter(Context context) { 
      this.mContext=context; 
    } 
 
    @Override 
    public int getCount() { 
      return mThumbIds.length; 
    } 
 
    @Override 
    public Object getItem(int position) { 
      return mThumbIds[position]; 
    } 
 
    @Override 
    public long getItemId(int position) { 
      // TODO Auto-generated method stub 
      return 0; 
    } 
 
    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 
      //定义一个ImageView,显示在GridView里 
      ImageView imageView; 
      if(convertView==null){ 
        imageView=new ImageView(mContext); 
        imageView.setLayoutParams(new GridView.LayoutParams(85, 85)); 
        imageView.setScaleType(ImageView.ScaleType.CENTER_CROP); 
        imageView.setPadding(8, 8, 8, 8); 
      }else{ 
        imageView = (ImageView) convertView; 
      } 
      imageView.setImageResource(mThumbIds[position]); 
      return imageView; 
    } 
     
 
     
  } 
  //展示图片 
  private Integer[] mThumbIds = { 
      R.drawable.sample_2, R.drawable.sample_3, 
      R.drawable.sample_4, R.drawable.sample_5, 
      R.drawable.sample_6, R.drawable.sample_7, 
      R.drawable.sample_0, R.drawable.sample_1, 
      R.drawable.sample_2, R.drawable.sample_3, 
      R.drawable.sample_4, R.drawable.sample_5, 
      R.drawable.sample_6, R.drawable.sample_7, 
      R.drawable.sample_0, R.drawable.sample_1, 
      R.drawable.sample_2, R.drawable.sample_3, 
      R.drawable.sample_4, R.drawable.sample_5, 
      R.drawable.sample_6, R.drawable.sample_7 
  }; 
} 

package com.example.draggridview; 
 
import android.app.Activity; 
import android.content.Context; 
import android.graphics.Bitmap; 
import android.graphics.PixelFormat; 
import android.graphics.Rect; 
import android.os.Handler; 
import android.os.Vibrator; 
import android.util.AttributeSet; 
import android.view.Gravity; 
import android.view.MotionEvent; 
import android.view.View; 
import android.view.WindowManager; 
import android.widget.AdapterView; 
import android.widget.GridView; 
import android.widget.ImageView; 
 
public class DragGridView extends GridView{ 
  /** 
   * DragGridView的item长按响应的时间， 默认是1000毫秒，也可以自行设置 
   */ 
  private long dragResponseMS = 1000; 
   
  /** 
   * 是否可以拖拽，默认不可以 
   */ 
  private boolean isDrag = false; 
   
  private int mDownX; 
  private int mDownY; 
  private int moveX; 
  private int moveY; 
  /** 
   * 正在拖拽的position 
   */ 
  private int mDragPosition; 
   
  /** 
   * 刚开始拖拽的item对应的View 
   */ 
  private View mStartDragItemView = null; 
   
  /** 
   * 用于拖拽的镜像，这里直接用一个ImageView 
   */ 
  private ImageView mDragImageView; 
   
  /** 
   * 震动器 
   */ 
  private Vibrator mVibrator; 
   
  private WindowManager mWindowManager; 
  /** 
   * item镜像的布局参数 
   */ 
  private WindowManager.LayoutParams mWindowLayoutParams; 
   
  /** 
   * 我们拖拽的item对应的Bitmap 
   */ 
  private Bitmap mDragBitmap; 
   
  /** 
   * 按下的点到所在item的上边缘的距离 
   */ 
  private int mPoint2ItemTop ;  
   
  /** 
   * 按下的点到所在item的左边缘的距离 
   */ 
  private int mPoint2ItemLeft; 
   
  /** 
   * DragGridView距离屏幕顶部的偏移量 
   */ 
  private int mOffset2Top; 
   
  /** 
   * DragGridView距离屏幕左边的偏移量 
   */ 
  private int mOffset2Left; 
   
  /** 
   * 状态栏的高度 
   */ 
  private int mStatusHeight;  
   
  /** 
   * DragGridView自动向下滚动的边界值 
   */ 
  private int mDownScrollBorder; 
   
  /** 
   * DragGridView自动向上滚动的边界值 
   */ 
  private int mUpScrollBorder; 
   
  /** 
   * DragGridView自动滚动的速度 
   */ 
  private static final int speed = 20; 
   
  /** 
   * item发生变化回调的接口 
   */ 
  private OnChanageListener onChanageListener; 
   
   
   
  public DragGridView(Context context) { 
    this(context, null); 
  } 
   
  public DragGridView(Context context, AttributeSet attrs) { 
    this(context, attrs, 0); 
  } 
 
  public DragGridView(Context context, AttributeSet attrs, int defStyle) { 
    super(context, attrs, defStyle); 
    mVibrator = (Vibrator) context.getSystemService(Context.VIBRATOR_SERVICE); 
    mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE); 
    mStatusHeight = getStatusHeight(context); //获取状态栏的高度 
     
  } 
   
  private Handler mHandler = new Handler(); 
   
  //用来处理是否为长按的Runnable 
  private Runnable mLongClickRunnable = new Runnable() { 
     
    @Override 
    public void run() { 
      isDrag = true; //设置可以拖拽 
      mVibrator.vibrate(50); //震动一下 
      mStartDragItemView.setVisibility(View.INVISIBLE);//隐藏该item 
       
      //根据我们按下的点显示item镜像 
      createDragImage(mDragBitmap, mDownX, mDownY); 
    } 
  }; 

  /** 
   * 设置回调接口 
   * @param onChanageListener 
   */ 
  public void setOnChangeListener(OnChanageListener onChanageListener){ 
    this.onChanageListener = onChanageListener; 
  } 
   
  /** 
   * 设置响应拖拽的毫秒数，默认是1000毫秒 
   * @param dragResponseMS 
   */ 
  public void setDragResponseMS(long dragResponseMS) { 
    this.dragResponseMS = dragResponseMS; 
  } 
 
  @Override 
  public boolean dispatchTouchEvent(MotionEvent ev) { 
    switch(ev.getAction()){ 
    case MotionEvent.ACTION_DOWN: 
      mDownX = (int) ev.getX(); 
      mDownY = (int) ev.getY(); 
       
      //根据按下的X,Y坐标获取所点击item的position 
      mDragPosition = pointToPosition(mDownX, mDownY); 
       
       
      if(mDragPosition == AdapterView.INVALID_POSITION){ 
        return super.dispatchTouchEvent(ev); 
      } 
       
      //使用Handler延迟dragResponseMS执行mLongClickRunnable 
      mHandler.postDelayed(mLongClickRunnable, dragResponseMS); 
       
      //根据position获取该item所对应的View 
      mStartDragItemView = getChildAt(mDragPosition - getFirstVisiblePosition()); 
       
      //下面这几个距离大家可以参考我的博客上面的图来理解下 
      mPoint2ItemTop = mDownY - mStartDragItemView.getTop(); 
      mPoint2ItemLeft = mDownX - mStartDragItemView.getLeft(); 
       
      mOffset2Top = (int) (ev.getRawY() - mDownY); 
      mOffset2Left = (int) (ev.getRawX() - mDownX); 
       
      //获取DragGridView自动向上滚动的偏移量，小于这个值，DragGridView向下滚动 
      mDownScrollBorder = getHeight() /4; 
      //获取DragGridView自动向下滚动的偏移量，大于这个值，DragGridView向上滚动 
      mUpScrollBorder = getHeight() * 3/4; 
       
       
       
      //开启mDragItemView绘图缓存 
      mStartDragItemView.setDrawingCacheEnabled(true); 
      //获取mDragItemView在缓存中的Bitmap对象 
      mDragBitmap = Bitmap.createBitmap(mStartDragItemView.getDrawingCache()); 
      //这一步很关键，释放绘图缓存，避免出现重复的镜像 
      mStartDragItemView.destroyDrawingCache(); 
       
       
      break; 
    case MotionEvent.ACTION_MOVE: 
      int moveX = (int)ev.getX(); 
      int moveY = (int) ev.getY(); 
       
      //如果我们在按下的item上面移动，只要不超过item的边界我们就不移除mRunnable 
      if(!isTouchInItem(mStartDragItemView, moveX, moveY)){ 
        mHandler.removeCallbacks(mLongClickRunnable); 
      } 
      break; 
    case MotionEvent.ACTION_UP: 
      mHandler.removeCallbacks(mLongClickRunnable); 
      mHandler.removeCallbacks(mScrollRunnable); 
      break; 
    } 
    return super.dispatchTouchEvent(ev); 
  } 

  /** 
   * 是否点击在GridView的item上面 
   * @param itemView 
   * @param x 
   * @param y 
   * @return 
   */ 
  private boolean isTouchInItem(View dragView, int x, int y){ 
    if(dragView == null){ 
      return false; 
    } 
    int leftOffset = dragView.getLeft(); 
    int topOffset = dragView.getTop(); 
    if(x < leftOffset || x > leftOffset + dragView.getWidth()){ 
      return false; 
    } 
     
    if(y < topOffset || y > topOffset + dragView.getHeight()){ 
      return false; 
    } 
     
    return true; 
  } 
   
   
 
  @Override 
  public boolean onTouchEvent(MotionEvent ev) { 
    if(isDrag && mDragImageView != null){ 
      switch(ev.getAction()){ 
      case MotionEvent.ACTION_MOVE: 
        moveX = (int) ev.getX(); 
        moveY = (int) ev.getY(); 
        //拖动item 
        onDragItem(moveX, moveY); 
        break; 
      case MotionEvent.ACTION_UP: 
        onStopDrag(); 
        isDrag = false; 
        break; 
      } 
      return true; 
    } 
    return super.onTouchEvent(ev); 
  } 

  /** 
   * 创建拖动的镜像 
   * @param bitmap 
   * @param downX 
   *     按下的点相对父控件的X坐标 
   * @param downY 
   *     按下的点相对父控件的X坐标 
   */ 
  private void createDragImage(Bitmap bitmap, int downX , int downY){ 
    mWindowLayoutParams = new WindowManager.LayoutParams(); 
    mWindowLayoutParams.format = PixelFormat.TRANSLUCENT; //图片之外的其他地方透明 
    mWindowLayoutParams.gravity = Gravity.TOP | Gravity.LEFT; 
    mWindowLayoutParams.x = downX - mPoint2ItemLeft + mOffset2Left; 
    mWindowLayoutParams.y = downY - mPoint2ItemTop + mOffset2Top - mStatusHeight; 
    mWindowLayoutParams.alpha = 0.55f; //透明度 
    mWindowLayoutParams.width = WindowManager.LayoutParams.WRAP_CONTENT;  
    mWindowLayoutParams.height = WindowManager.LayoutParams.WRAP_CONTENT;  
    mWindowLayoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE  
          | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE ; 
      
    mDragImageView = new ImageView(getContext());  
    mDragImageView.setImageBitmap(bitmap);  
    mWindowManager.addView(mDragImageView, mWindowLayoutParams);  
  } 
   

  /** 
   * 从界面上面移动拖动镜像 
   */ 
  private void removeDragImage(){ 
    if(mDragImageView != null){ 
      mWindowManager.removeView(mDragImageView); 
      mDragImageView = null; 
    } 
  } 

  /** 
   * 拖动item，在里面实现了item镜像的位置更新，item的相互交换以及GridView的自行滚动 
   * @param x 
   * @param y 
   */ 
  private void onDragItem(int moveX, int moveY){ 
    mWindowLayoutParams.x = moveX - mPoint2ItemLeft + mOffset2Left; 
    mWindowLayoutParams.y = moveY - mPoint2ItemTop + mOffset2Top - mStatusHeight; 
    mWindowManager.updateViewLayout(mDragImageView, mWindowLayoutParams); //更新镜像的位置 
    onSwapItem(moveX, moveY); 
     
    //GridView自动滚动 
    mHandler.post(mScrollRunnable); 
  } 

  /** 
   * 当moveY的值大于向上滚动的边界值，触发GridView自动向上滚动 
   * 当moveY的值小于向下滚动的边界值，触犯GridView自动向下滚动 
   * 否则不进行滚动 
   */ 
  private Runnable mScrollRunnable = new Runnable() { 
     
    @Override 
    public void run() { 
      int scrollY; 
      if(moveY > mUpScrollBorder){ 
         scrollY = speed; 
         mHandler.postDelayed(mScrollRunnable, 25); 
      }else if(moveY < mDownScrollBorder){ 
        scrollY = -speed; 
         mHandler.postDelayed(mScrollRunnable, 25); 
      }else{ 
        scrollY = 0; 
        mHandler.removeCallbacks(mScrollRunnable); 
      } 
       
      //当我们的手指到达GridView向上或者向下滚动的偏移量的时候，可能我们手指没有移动，但是DragGridView在自动的滚动 
      //所以我们在这里调用下onSwapItem()方法来交换item 
      onSwapItem(moveX, moveY); 
       
       
      smoothScrollBy(scrollY, 10); 
    } 
  }; 

  /** 
   * 交换item,并且控制item之间的显示与隐藏效果 
   * @param moveX 
   * @param moveY 
   */ 
  private void onSwapItem(int moveX, int moveY){ 
    //获取我们手指移动到的那个item的position 
    int tempPosition = pointToPosition(moveX, moveY); 
     
    //假如tempPosition 改变了并且tempPosition不等于-1,则进行交换 
    if(tempPosition != mDragPosition && tempPosition != AdapterView.INVALID_POSITION){ 
      if(onChanageListener != null){ 
        onChanageListener.onChange(mDragPosition, tempPosition); 
      } 
       
      getChildAt(tempPosition - getFirstVisiblePosition()).setVisibility(View.INVISIBLE);//拖动到了新的item,新的item隐藏掉 
      getChildAt(mDragPosition - getFirstVisiblePosition()).setVisibility(View.VISIBLE);//之前的item显示出来 
       
      mDragPosition = tempPosition; 
    } 
  } 

   
  /** 
   * 停止拖拽我们将之前隐藏的item显示出来，并将镜像移除 
   */ 
  private void onStopDrag(){ 
    View view = getChildAt(mDragPosition - getFirstVisiblePosition()); 
    if(view != null){ 
      view.setVisibility(View.VISIBLE); 
    } 
    ((DragAdapter)this.getAdapter()).setItemHide(-1); 
    removeDragImage(); 
  } 

  /** 
   * 获取状态栏的高度 
   * @param context 
   * @return 
   */ 
  private static int getStatusHeight(Context context){ 
    int statusHeight = 0; 
    Rect localRect = new Rect(); 
    ((Activity) context).getWindow().getDecorView().getWindowVisibleDisplayFrame(localRect); 
    statusHeight = localRect.top; 
    if (0 == statusHeight){ 
      Class<?> localClass; 
      try { 
        localClass = Class.forName("com.android.internal.R$dimen"); 
        Object localObject = localClass.newInstance(); 
        int i5 = Integer.parseInt(localClass.getField("status_bar_height").get(localObject).toString()); 
        statusHeight = context.getResources().getDimensionPixelSize(i5); 
      } catch (Exception e) { 
        e.printStackTrace(); 
      }  
    } 
    return statusHeight; 
  } 

  /** 
   * 
   * @author xiaanming 
   * 
   */ 
  public interface OnChanageListener{ 
     
    /** 
     * 当item交换位置的时候回调的方法，我们只需要在该方法中实现数据的交换即可 
     * @param form 
     *     开始的position 
     * @param to 
     *     拖拽到的position 
     */ 
    public void onChange(int form, int to); 
  } 
} 

首先看DragGridView的事件分发方法，不了解Android事件分发的可以先去了解下，Android事件分发对于自定义控件很重要，简单说下，当我们点击DragGridView的Item,先会去执行dispatchTouchEvent()方法将事件分发下去，所以我们要重写dispatchTouchEvent()方法在手指按下的时候根据pointToPosition()方法来获取我们按下的item的position,根据getChildAt()方法来获取该position上面所对应的View, 并且开启长按的定时器，默认时间为1000毫秒，如果在1000毫秒内手指抬起或者手指在屏幕上滑动出了该item，则取消长按定时器，否则就表示可以进行拖拽，手机友好的震动一下，隐藏我们长按的Item，屏幕调用createDragImage()方法来创建我们长按的item的镜像，创建Item的镜像使用的是WindowManager类，该类可以创建一个窗体显示在Activity之上，
再此之前大家先要理解这几个距离，理解这几个距离之前要首先知道getRawX(),getRawY()和getX(),getY()的区别，getRawX(),getRawY()是相对于屏幕的原点的距离，而getX(),getY()是相对于控件左上方的点的距离，为了方便大家理解我用Word简单的画了下图，画得不好，大家将就的看下，红色框框为我们的GridView

• mPoint2ItemTop 手指按下的点到该Item的上边缘的距离，如上图的1号线
• mPoint2ItemLeft 手指按下的点到该Item的左边缘的距离，如上图的2号线
• mOffset2Top  DragGridView的上边缘到屏幕上边缘的距离，如上图的3号线，这个距离包裹状态栏，标题栏，或者一些在DragGridView上面的布局的高度，这个很重要我们现实Item镜像需要用到
• mOffset2Left DragGridView的左边缘到屏幕左边缘的距离，如上图的4号线，我这个Demo的这个距离为0，因为我设置DragGridView的宽度为充满屏幕，但是我们要考虑假如DragGridView与屏幕左边缘设置了间隙或者左边有其他的布局的情形
• mDownScrollBorder 这个距离表示当DragGridView的item过多的时候，手机一屏显示不完全，我们拖动Item镜像到这个高度的时候，DragGridView自动向下滚动，如上图的5号线
• .mUpScrollBorder 这个和mDownScrollBorder相反，当我们大于这个高度的时候，DragGridView自动向上滚动，如上图的6号线

理解了这六个距离，我们就来看看创建Item镜像的方法里面，其他的我不多说，首先设置format为PixelFormat.TRANSLUCENT，表示除了我们显示图片和文字的其他地方为透明，之后就是x，y这两个距离的计算，计算的是item的左上角的坐标，理解了上面这六个距离我们很容易得出x,y的坐标，可是你会发现y的坐标减去了状态栏的高度，这点大家需要注意下，另外我们需要获取item的绘制缓存的Bitmap对象，然后将Bitmap设置到一个ImageView上面，为什么要这么做呢？如果调用addView()方法将item 直接添加到WindowManager里面，会有异常产生，因为item已经有了自己归属的父容器DragGridView，所有我们这里使用一个ImageView来代替item添加到WindowManager里面

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
  xmlns:tools="http://schemas.android.com/tools" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent" > 
 
  <com.example.draggridview.DragGridView 
    android:id="@+id/dragGridView" 
    android:listSelector="@android:color/transparent" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:cacheColorHint="@android:color/transparent" 
    android:verticalSpacing="10dip" 
    android:horizontalSpacing="10dip" 
    android:stretchMode="columnWidth"  
    android:gravity="center"  
    android:numColumns="3" > 
  </com.example.draggridview.DragGridView> 
 
</RelativeLayout> 

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
  android:layout_width="fill_parent" 
  android:layout_height="wrap_content" 
  android:background="@android:color/transparent" > 
 
  <ImageView 
    android:id="@+id/item_image" 
    android:scaleType="centerCrop" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_centerHorizontal="true" > 
  </ImageView> 
 
  <TextView 
    android:id="@+id/item_text" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_below="@+id/item_image" 
    android:layout_centerHorizontal="true" > 
  </TextView> 
 
</RelativeLayout> 

package com.example.draggridview; 
 
import java.util.ArrayList; 
import java.util.Collections; 
import java.util.HashMap; 
import java.util.List; 
 
import android.app.Activity; 
import android.os.Bundle; 
import android.widget.SimpleAdapter; 
 
import com.example.draggridview.DragGridView.OnChanageListener; 

public class MainActivity extends Activity { 
  private List<HashMap<String, Object>> dataSourceList = new ArrayList<HashMap<String, Object>>(); 
 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
 
    DragGridView mDragGridView = (DragGridView) findViewById(R.id.dragGridView); 
    for (int i = 0; i < 30; i++) { 
      HashMap<String, Object> itemHashMap = new HashMap<String, Object>(); 
      itemHashMap.put("item_image",R.drawable.com_tencent_open_notice_msg_icon_big); 
      itemHashMap.put("item_text", "拖拽 " + Integer.toString(i)); 
      dataSourceList.add(itemHashMap); 
    } 
     
 
    final SimpleAdapter mSimpleAdapter = new SimpleAdapter(this, dataSourceList, 
        R.layout.grid_item, new String[] { "item_image", "item_text" }, 
        new int[] { R.id.item_image, R.id.item_text }); 
     
    mDragGridView.setAdapter(mSimpleAdapter); 
     
    mDragGridView.setOnChangeListener(new OnChanageListener() { 
       
      @Override 
      public void onChange(int from, int to) { 
        HashMap<String, Object> temp = dataSourceList.get(from); 
        //直接交互item 
//       dataSourceList.set(from, dataSourceList.get(to)); 
//       dataSourceList.set(to, temp); 
//       dataSourceList.set(to, temp); 
         
         
        //这里的处理需要注意下 
        if(from < to){ 
          for(int i=from; i<to; i++){ 
            Collections.swap(dataSourceList, i, i+1); 
          } 
        }else if(from > to){ 
          for(int i=from; i>to; i--){ 
            Collections.swap(dataSourceList, i, i-1); 
          } 
        } 
         
        dataSourceList.set(to, temp); 
         
        mSimpleAdapter.notifyDataSetChanged(); 
         
         
      } 
    }); 
     
  } 
 
} 

HashMap<String, Object> temp = dataSourceList.get(from); 
        //直接交互item 
//       dataSourceList.set(from, dataSourceList.get(to)); 
//       dataSourceList.set(to, temp);