Android控件拖动的实现

              这个也是从网上得到的代码，例子比较简单，但是如果有需要此功能的，这个例子可以提供很多提示，首先，给个截图

这个是拖动以后的效果，一个imageview和一个button控件，提供两份代码下载吧，一份是只有一个Button的，另一份就是像上图，就是多了一个imagview！先看下代码吧，比较简单：

public class DraftTest extends Activity implements OnTouchListener{
	/** Called when the activity is first created. */
	int screenWidth;
	int screenHeight;
	int lastX;
	int lastY;
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);

		DisplayMetrics dm = getResources().getDisplayMetrics();
		screenWidth = dm.widthPixels;
		screenHeight = dm.heightPixels - 50;
		Button button=(Button)findViewById(R.id.btn);
		ImageView imageView=(ImageView)findViewById(R.id.btn2);
		imageView.setOnTouchListener(this);
		button.setOnTouchListener(this);
	}

	@Override
	public boolean onTouch(View v, MotionEvent event) {
		// TODO Auto-generated method stub
		int action=event.getAction();
		Log.i("@@@@@@", "Touch:"+action);
		//Toast.makeText(DraftTest.this, "λ�ã�"+x+","+y, Toast.LENGTH_SHORT).show();
		switch(action){
		case MotionEvent.ACTION_DOWN:
			lastX = (int) event.getRawX();
			lastY = (int) event.getRawY();
			break;
			/**
			 * layout(l,t,r,b)
			 * l  Left position, relative to parent 
            t  Top position, relative to parent 
            r  Right position, relative to parent 
            b  Bottom position, relative to parent  
			 * */
		case MotionEvent.ACTION_MOVE:
			int dx =(int)event.getRawX() - lastX;
			int dy =(int)event.getRawY() - lastY;
		
			int left = v.getLeft() + dx;
			int top = v.getTop() + dy;
			int right = v.getRight() + dx;
			int bottom = v.getBottom() + dy;					
			if(left < 0){
				left = 0;
				right = left + v.getWidth();
			}					
			if(right > screenWidth){
				right = screenWidth;
				left = right - v.getWidth();
			}					
			if(top < 0){
				top = 0;
				bottom = top + v.getHeight();
			}					
			if(bottom > screenHeight){
				bottom = screenHeight;
				top = bottom - v.getHeight();
			}					
			v.layout(left, top, right, bottom);
			Log.i("@@@@@@", "position��" + left +", " + top + ", " + right + ", " + bottom);   
			lastX = (int) event.getRawX();
			lastY = (int) event.getRawY();					
			break;
		case MotionEvent.ACTION_UP:
			break;        		
		}
		return false;	
	}
}

高度减去50是减去状态栏和标题栏的高度。

case MotionEvent.ACTION_DOWN:
			lastX = (int) event.getRawX();
			lastY = (int) event.getRawY();
			break;

然后获取控件一开始的位置，然后在ACTION_MOVIE中：

int dx =(int)event.getRawX() - lastX;
			int dy =(int)event.getRawY() - lastY;
		
			int left = v.getLeft() + dx;
			int top = v.getTop() + dy;
			int right = v.getRight() + dx;
			int bottom = v.getBottom() + dy;					
			if(left < 0){
				left = 0;
				right = left + v.getWidth();
			}					
			if(right > screenWidth){
				right = screenWidth;
				left = right - v.getWidth();
			}					
			if(top < 0){
				top = 0;
				bottom = top + v.getHeight();
			}					
			if(bottom > screenHeight){
				bottom = screenHeight;
				top = bottom - v.getHeight();
			}					
			v.layout(left, top, right, bottom);
			Log.i("@@@@@@", "position��" + left +", " + top + ", " + right + ", " + bottom);   
			lastX = (int) event.getRawX();
			lastY = (int) event.getRawY();	

getLeft()方法得到的是控件坐标距离父控件原点(左上角，坐标（0，0）)的x轴距离，getReght()是控件右边距离父控件原点的x轴距离，同理，getTop和getButtom是距离的y轴距离。

if(left < 0){
				left = 0;
				right = left + v.getWidth();
			}					
			if(right > screenWidth){
				right = screenWidth;
				left = right - v.getWidth();
			}					
			if(top < 0){
				top = 0;
				bottom = top + v.getHeight();
			}					
			if(bottom > screenHeight){
				bottom = screenHeight;
				top = bottom - v.getHeight();
			}	

这里的判断是为了是控件不超出屏幕以外，即：到达边界以后，不能再移动。

v.layout(left, top, right, bottom);

设置View的位置。

有一点忘记说了，就是像ImageView和TextView这些控件，要想实现拖动，要在xml文件中设置它的clickable为true。

android:clickable="true"

就这样，这些就是这个demo的全部内容。

最后，是代码的下载地址：

http://download.csdn.net/detail/aomandeshangxiao/4187376，

http://download.csdn.net/detail/aomandeshangxiao/4189910