本文介绍如何在Android的GridView中实现长按拖拽效果。重点在于理解DragGVAdapter.java文件中的事件处理顺序，即onInterceptTouchEvent() -> onItemLongClick() -> onTouchEvent()，ACTION_MOVE和ACTION_UP的操作。在onTouchEvent()方法内添加映像处理，以避免在滑动时出现不必要的映像。实测在Samsung S4设备上运行正常。
DragGridViewEx.java文件：
package com.smiling.draggridview;
/*
* onInterceptTouchEvent() -> onItemLongClick() -> onTouchEvent()->ACTION_MOVE->ACTION_UP;
*
* */
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Color;
import android.util.AttributeSet;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.WindowManager;
import android.widget.AdapterView;
import android.widget.GridView;
import android.widget.ImageView;
//以下为自定义GridView控件;
public class DragGridViewEx extends GridView{
private WindowManager windowManager;// windows窗口控制类
private WindowManager.LayoutParams windowParams;// 用于控制拖拽项的显示的参数
private ImageView dragImageView;// 被拖拽的项(item)，其实就是一个ImageView\
private View itemView=null;
private Bitmap bm;
private ImageView imageView;
private View dragger;
private int dragSrcPosition;// 手指拖动项在列表中的原始位置
private int dragPosition;// 手指点击准备拖动的时候,当前拖动项在列表中的位置.
private int dragPointX;
private int dragPointY;// 在当前数据项中的位置
private int dragOffsetX;
private int dragOffsetY;// 当前视图和屏幕的距离(这里只使用了y方向上)
private int upScrollBounce;// 拖动的时候，开始向上滚动的边界
private int downScrollBounce;// 拖动的时候，开始向下滚动的边界
private int tempChangeId;
private boolean isDoTouch = false;
private boolean hasAdd=false;
//=========================================================================================================
public DragGridViewEx(Context context) {
super(context);
// TODO 自动生成的构造函数存根
}
public DragGridViewEx(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO 自动生成的构造函数存根
}
public DragGridViewEx(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
// TODO 自动生成的构造函数存根
}
//==========================================================================================================
public void setDoTouch(boolean b){
this.isDoTouch=b;
this.hasAdd=false;
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
{
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
{
int x = (int) ev.getX();
int y = (int) ev.getY();
this.tempChangeId=dragSrcPosition = dragPosition = pointToPosition(x, y);
System.out.println("getY()="+y+","+"dragPosition="+dragPosition);
System.out.println("getFirstVisiblePosition()="+getFirstVisiblePosition());
// 无效不进行处理
if (dragPosition == AdapterView.INVALID_POSITION) {
return super.onInterceptTouchEvent(ev);
}
// 获取当前位置的视图(可见状态)
itemView = getChildAt(dragPosition-getFirstVisiblePosition());
dragPointX = x - itemView.getLeft();
dragPointY = y - itemView.getTop(); //不可见的项不算;
dragOffsetX = (int) (ev.getRawX() - x);
dragOffsetY = (int) (ev.getRawY() - y);
//每个项中可能有其他的文字之类的东西,所以要获取 R.id.drag_gridview_image;
dragger = itemView.findViewById(R.id.drag_gridview_image);
if (dragger != null &&dragPointX>dragger.getLeft()
&&dragPointX<dragger.getRight()
&&dragPointY>dragger.getTop()
&&dragPointY<dragger.getBottom()) {
upScrollBounce = getHeight() / 4; // 取得向上滚动的边际，大概为该控件的1/3
downScrollBounce = getHeight() * 3 / 4;// 取得向下滚动的边际，大概为该控件的2/3
System.out.println("Here....");
itemView.setDrawingCacheEnabled(true);// 开启cache.
bm= Bitmap.createBitmap(itemView.getDrawingCache());// 根据cache创建一个新的bitmap对象.
startDrag(bm, x, y);// 初始化影像;
}
}
}
}
return super.onInterceptTouchEvent(ev);
}
private void startDrag(Bitmap bm, int x, int y) {
// stopDrag();
/***
* 初始化window.
*/
windowParams = new WindowManager.LayoutParams();
windowParams.gravity = Gravity.TOP| Gravity.LEFT;
windowParams.x = x - dragPointX + dragOffsetX;
windowParams.y = y - dragPointY + dragOffsetY; //getTop()+dragOffset;
windowParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
windowParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
windowParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE// 不需获取焦点
| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE// 不需接受触摸事件
| WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON// 保持设备常开，并保持亮度不变。
| WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN;// 窗口占满整个屏幕，忽略周围的装饰边框（例如状态栏）。此窗口需考虑到装饰边框的内容。
windowParams.windowAnimations = 0;
imageView = new ImageView(getContext());
imageView.setImageBitmap(bm);
windowManager = (WindowManager) getContext().getSystemService("window");
// windowManager.addView(imageView, windowParams); //注意不在这里添加;
dragImageView = imageView;
}
//===========================================================================================================
/**
* 触摸事件处理
*/
@Override
public boolean onTouchEvent(MotionEvent ev) {
// item的view不为空，且获取的dragPosition有效
if (dragImageView!=null&&dragPosition != INVALID_POSITION && isDoTouch==true) {
if(!this.hasAdd){
windowManager.addView(imageView, windowParams);
this.hasAdd=true;
}
int action = ev.getAction();
switch (action) {
case MotionEvent.ACTION_UP:
System.out.println("ACTION_UP");
if(!this.dragger.isShown()){
this.dragger.setVisibility(View.VISIBLE);
System.out.println("VISIBLE");
}
int upX = (int) ev.getX();
int upY = (int) ev.getY();
stopDrag();
onDrop(upX,upY);
isDoTouch=false; //若没有这个，就不会触发onItemClick事件了
hasAdd=false;
break;
case MotionEvent.ACTION_MOVE:
//System.out.println("ACTION_MOVE");
if(this.dragger.isShown()){
this.dragger.setVisibility(View.INVISIBLE);
}
int moveX = (int)ev.getX();
int moveY = (int) ev.getY();
onDrag(moveX,moveY);
break;
case MotionEvent.ACTION_DOWN:
//longClick之后不会执行;
System.out.println("ACTION_DOWN");
int downX = (int)ev.getX();
int downY = (int) ev.getY();
break;
default:
break;
}
return true;
}
return super.onTouchEvent(ev);
}
//=======================================================================================================
public void onDrag(int x, int y) {
if (dragImageView != null) {
windowParams.alpha = 0.7f;// 透明度
windowParams.x = x - dragPointX + dragOffsetX;
windowParams.y = y - dragPointY + dragOffsetY;// 移动y值.//记得要加上dragOffset，windowManager计算的是整个屏幕.(标题栏和状态栏都要算上)
windowManager.updateViewLayout(dragImageView, windowParams);// 时时移动.
}
int tempPosition = pointToPosition(x, y);
if (tempPosition != INVALID_POSITION) {
dragPosition = tempPosition;
}
onChange(x,y);
// 滚动
if (y < upScrollBounce || y > downScrollBounce) {
// 使用setSelection来实现滚动
setSelection(dragPosition);
}
}
public void onChange(int x,int y){
if(dragPosition<getAdapter().getCount()){
DragGVAdapter adapter = (DragGVAdapter)getAdapter();
if(this.tempChangeId!=this.dragPosition){
adapter.update(tempChangeId,dragPosition);
this.tempChangeId=this.dragPosition;
}
}
int tempPosition=pointToPosition(x,y);
if(tempPosition!=INVALID_POSITION){
this.dragPosition=tempPosition;
}
}
public void stopDrag() {
if (dragImageView != null) {
windowManager.removeView(dragImageView);
dragImageView = null;
}
}
public void onDrop(int x,int y) {
// 数据交换
if (dragPosition < getAdapter().getCount()) {
DragGVAdapter adapter = (DragGVAdapter)getAdapter();
adapter.lastUpdate();
}
}
}
DragGVAdapter.java文件：
package com.smiling.draggridview;
import java.util.ArrayList;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
public class DragGVAdapter extends BaseAdapter{
private Context context;
private ArrayList<Integer> arrayDrawables;
private boolean isHide=false;
private int endPosition=-1;
public DragGVAdapter(Context c,ArrayList<Integer> pics){
this.context=c;
this.arrayDrawables=pics;
}
@Override
public int getCount() {
// TODO 自动生成的方法存根
return this.arrayDrawables.size();
}
@Override
public Object getItem(int arg0) {
// TODO 自动生成的方法存根
return null;
}
@Override
public long getItemId(int arg0) {
// TODO 自动生成的方法存根
return arg0;
}
@Override
public View getView(int position, View v, ViewGroup vg) {
// TODO 自动生成的方法存根
LayoutInflater inflater=LayoutInflater.from(context);
v=inflater.inflate(R.layout.drag_gridview_item,null);
System.out.println("POSITION="+position); //连续输出两次POSITION=0;
if(position!=endPosition){
ImageView imageview=(ImageView)v.findViewById(R.id.drag_gridview_image);
imageview.setImageResource(this.arrayDrawables.get(position));
imageview.setScaleType(ImageView.ScaleType.FIT_XY);
}else if(position==endPosition){
ImageView imageview=(ImageView)v.findViewById(R.id.drag_gridview_image);
imageview.setImageResource(this.arrayDrawables.get(position));
imageview.setScaleType(ImageView.ScaleType.FIT_XY);
imageview.setVisibility(View.INVISIBLE);
}
return v;
}
public void update(int start, int down) {
this.endPosition=down;
System.out.println("END="+endPosition);
int drawable_id = arrayDrawables.get(start);
arrayDrawables.remove(start);
arrayDrawables.add(down, drawable_id);
notifyDataSetChanged();
}
public void lastUpdate(){
this.endPosition=-1;
notifyDataSetChanged();
}
}
这里需要注意几点，首先是方法的执行顺序，是先onInterceptTouchEvent()，然后是onItemLongClick()，接着onTouchEvent()，ACTION_MOVE->ACTION_UP;注意映像应该在onTouchEvent方法中添加，而不能在onInterceptTouchEvent()方法中添加，否则GridView上下滑动也会出现映像。
Sumsang S4实测截图如下：
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