Android下图片或按钮等可拖动到任意位置的效果实现源码

public class DraftTest extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_draft_test);

DisplayMetrics dm = getResources().getDisplayMetrics();
final int screenWidth = dm.widthPixels;
final int screenHeight = dm.heightPixels - 50;
// 拖动的按钮
final Button b = (Button) findViewById(R.id.startBtn);

// 添加触摸事件
b.setOnTouchListener(new OnTouchListener() {
int lastX, lastY; // 记录移动的最后的位置

public boolean onTouch(View v, MotionEvent event) {
// 获取Action
int ea = event.getAction();
Log.i("TAG", "Touch:" + ea);
switch (ea) {
case MotionEvent.ACTION_DOWN: // 按下
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: // 移动
// 移动中动态设置位置
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("aaa", "position：" + left + ", " + top + ", " + right
+ ", " + bottom);
// 将当前的位置再次设置
lastX = (int) event.getRawX();
lastY = (int) event.getRawY();
break;
case MotionEvent.ACTION_UP: // 脱离
break;
}
return false;
}
});
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_draft_test, menu);
return true;
}

}

<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"
android:padding="0px"
tools:context=".DraftTest" >

<Button
android:id="@+id/startBtn"
android:text="tuodongdeanniu"
android:layout_centerInParent="true"
android:layout_width="wrap_content" android:layout_height="wrap_content"/>

</RelativeLayout>