为什么我滑屏时不显示"默认的Toast"呢

public class MainActivity extends Activity implements OnGestureListener {

@Override
public boolean onDown(MotionEvent e) {
    // TODO Auto-generated method stub
    return false;
}

@Override
public void onShowPress(MotionEvent e) {
    // TODO Auto-generated method stub

}

@Override
public boolean onSingleTapUp(MotionEvent e) {
    // TODO Auto-generated method stub
    return false;
}

@Override
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
    // TODO Auto-generated method stub
    return false;
}

@Override
public void onLongPress(MotionEvent e) {
    // TODO Auto-generated method stub

}

@SuppressLint("ShowToast")
@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
    if(velocityX < 0){ 
     Toast toast=Toast.makeText(getApplicationContext(), "默认的Toast", Toast.LENGTH_SHORT); }
    if(velocityX > 0){ 
         Toast toast=Toast.makeText(getApplicationContext(), "默认的Toast", Toast.LENGTH_SHORT); }
    if(velocityY < 0){ 
         Toast toast=Toast.makeText(getApplicationContext(), "默认的Toast", Toast.LENGTH_SHORT); }
    if(velocityY > 0){ 
         Toast toast=Toast.makeText(getApplicationContext(), "默认的Toast", Toast.LENGTH_SHORT); }
    return false;
}



}  

。。因为你只是初始化那个Toast，没有调用show方法，正确应该是：
Toast.makeText(getApplicationContext(), "默认的Toast", Toast.LENGTH_SHORT).show();