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：

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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。

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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：

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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。

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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。

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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。

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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