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