view 移动 不超过 边缘

下面是一个拖动view时 view不会超出屏幕，即view不会被盖住的小例子

public class DragButtonActivity extends Activity implements OnTouchListener {

/** Called when the activity is first created. */

int[] temp = new int[] { 0, 0 };

int display_x, display_y = 800;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

final Button btn = (Button) findViewById(R.id.btn);

display_x = getWindowManager().getDefaultDisplay().getWidth();

View v = getWindow().findViewById(Window.ID_ANDROID_CONTENT);

v.measure(0, 0);

display_y = v.getMeasuredHeight();

showLog("display_y = " + display_y);

btn.setOnTouchListener(this);

}

@Override

public boolean onTouch(View v, MotionEvent event) {

int eventaction = event.getAction();

// Log.i("touch", "onTouchEvent:" + eventaction);

int x = (int) event.getRawX();

int y = (int) event.getRawY();

int w = v.getWidth(), h = v.getHeight();

switch (eventaction) {

case MotionEvent.ACTION_DOWN: // touch down so check if the

temp[0] = (int) event.getX();

temp[1] = (int) (y - v.getTop());

showLog("y = " + y + "; v.getTop() " + v.getTop()

+ "; (y - v.getTop()) = " + (y - v.getTop())

+ "; event.getY() = " + event.getY());

display_y = getWindow().findViewById(Window.ID_ANDROID_CONTENT)

.getHeight();

showLog("display_y = " + display_y);

break;

case MotionEvent.ACTION_MOVE: // touch drag with the ball

int l = (x - temp[0] <= 0) ? 0

: ((x - temp[0] + w > display_x) ? (display_x - w)

: (x - temp[0]));

int r = (l + w);

int t = (y - temp[1] <= 0) ? 0

: ((y - temp[1] + h > display_y) ? (display_y - h)

: (y - temp[1]));

int b = t + h;

v.layout(l, t, r, b);

v.postInvalidate();

break;

case MotionEvent.ACTION_UP:

break;

}

return false;

}

void showLog(String content) {

Log.i("touch", "------------------------:" + content);

}

}