如何抓住地图平移和缩放真的完成了？

Question

我正在尝试编写一个应用程序,它将动态加载数据,以便在用户平移或缩放时进行映射.

我需要跟踪地图何时完成以更改其视图状态(停止平移或缩放),然后加载新的数据部分以创建标记.但实际上Google Maps API没有任何事件来处理这个问题.

有一些方法,比如创建一个空的叠加来控制onTouch事件等等,但是地图平移可能会在用户完成触摸后持续很长时间,因为GMaps会使用某种惯性来使平移更平滑.

我试图子类,MapView但它的draw()方法是final因此它不能被覆盖.

有任何想法如何精确处理平移和缩放整理？

Answer 1

发现了研究时间和一些决定.它有一些缺点和优点,我将进一步描述.

我们应该做的主要是覆盖一些MapView的方法来处理它的绘图行为.如果我们不能覆盖draw()方法,我们应该找到另一种方法.可以覆盖View中的另一个派生 - computeScroll()方法.随着地图继续填充,它被重复调用.我们所要做的就是设置一些时间阈值来捕获这次是否再次调用computeScroll.
这是我做的:

import java.util.Timer;
import java.util.TimerTask;

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;

import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapView;

public class EnhancedMapView extends MapView {
public interface OnZoomChangeListener {
    public void onZoomChange(MapView view, int newZoom, int oldZoom);
}

public interface OnPanChangeListener {
    public void onPanChange(MapView view, GeoPoint newCenter, GeoPoint oldCenter);
}

private EnhancedMapView _this;

    // Set this variable to your preferred timeout
private long events_timeout = 500L;
private boolean is_touched = false;
private GeoPoint last_center_pos;
private int last_zoom;
private Timer zoom_event_delay_timer = new Timer();
private Timer pan_event_delay_timer = new Timer();

private EnhancedMapView.OnZoomChangeListener zoom_change_listener;
private EnhancedMapView.OnPanChangeListener pan_change_listener;


public EnhancedMapView(Context context, String apiKey) {
    super(context, apiKey);
    _this = this;
    last_center_pos = this.getMapCenter();
    last_zoom = this.getZoomLevel();
}

public EnhancedMapView(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public EnhancedMapView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
}

public void setOnZoomChangeListener(EnhancedMapView.OnZoomChangeListener l) {
    zoom_change_listener = l;
}

public void setOnPanChangeListener(EnhancedMapView.OnPanChangeListener l) {
    pan_change_listener = l;
}

@Override
public boolean onTouchEvent(MotionEvent ev) {
    if (ev.getAction() == 1) {
        is_touched = false;
    } else {
        is_touched = true;
    }

    return super.onTouchEvent(ev);
}

@Override
public void computeScroll() {
    super.computeScroll();

    if (getZoomLevel() != last_zoom) {
                    // if computeScroll called before timer counts down we should drop it and start it over again
        zoom_event_delay_timer.cancel();
        zoom_event_delay_timer = new Timer();
        zoom_event_delay_timer.schedule(new TimerTask() {
            @Override
            public void run() {
                zoom_change_listener.onZoomChange(_this, getZoomLevel(), last_zoom);
                last_zoom = getZoomLevel();
            }
        }, events_timeout);
    }

    // Send event only when map's center has changed and user stopped touching the screen
    if (!last_center_pos.equals(getMapCenter()) || !is_touched) {
        pan_event_delay_timer.cancel();
        pan_event_delay_timer = new Timer();
        pan_event_delay_timer.schedule(new TimerTask() {
            @Override
            public void run() {
                pan_change_listener.onPanChange(_this, getMapCenter(), last_center_pos);
                last_center_pos = getMapCenter();
            }
        }, events_timeout);
    }
}

}

然后你应该在MapActivity中注册事件处理程序,如下所示:

public class YourMapActivity extends MapActivity {

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    mv = new EnhancedMapView(this, "<your Maps API key here>");

    mv.setClickable(true);
    mv.setBuiltInZoomControls(true);

    mv.setOnZoomChangeListener(new EnhancedMapView.OnZoomChangeListener() {
        @Override
        public void onZoomChange(MapView view, int newZoom, int oldZoom) {
            Log.d("test", "zoom changed from " + oldZoom + " to " + newZoom);
        }
    }
    mv.setOnPanChangeListener(new EnhancedMapView.OnPanChangeListener() {
        public void onPanChange(MapView view, GeoPoint newCenter, GeoPoint oldCenter) {
            Log.d("test", "center changed from " + oldCenter.getLatitudeE6() + "," + oldCenter.getLongitudeE6() + " to " + newCenter.getLatitudeE6() + "," + newCenter.getLongitudeE6());
        }
    }
}

那么这种方法的优缺点呢？
优点:
- 事件处理方式地图被平移或缩放.触摸事件,使用的硬件键,甚至以编程方式触发的事件都被处理(如setZoom()或animate()方法).
- 如果用户快速点击几次缩放按钮,则可以跳过不必要的数据加载.只有在点击停止后才会触发事件.
缺点:
- 取消缩放或平移动作是不可能的(也许我将来会添加此功能)

希望这个小课程能帮到你.