使用谷歌路线API地图视图中绘制方向 - 解码折线 [英] Map View draw directions using google Directions API - decoding polylines

问题描述

我想使用谷歌API的方向上显示我的MapView的方向，但我有困难的JSON响应获取数据。我能得到的水平和分的字符串，但不能工作，如何去code他们点在地图上。

I'm trying to use the Google directions API to show directions on my mapview but I am having difficulties getting the data from the JSON response. I can get the "levels" and "points" strings but can't work out how to decode them to points on the map.

任何帮助将是非常美联社preciated。

Any help would be much appreciated.

推荐答案

我可以去code他们为你，加上一流的下方，然后调用你的code像这样一类：

I have a class which can decode them for you, add the class below then call in your code like this:

int[] decodedZoomLevels = PolylineDecoder.decodeZoomLevels(levels);
GeoPoint[] gPts = PolylineDecoder.decodePoints(points, decodedZoomLevels.length);

其中，分和水平你是从JSON响应已提取的数据。然后，您可以通过geopoints数组绘制他们之间的线，以显示你的方向。

where points and levels are the data you've extracted from the JSON response. You can then go through the array of geopoints drawing a line between them to display your directions.

希望这有助于！肯尼

编辑：这似乎是谷歌的方向API不再返回缩放级别字符串作为JSON响应的一部分，不过不用担心，所有我们使用本作是检查点的数量，所以我们可以简单地把这些成一个列表，如：

It would seem that the google directions API no longer returns the zoom levels string as part of the JSON response, not to worry though, all we were using this for was to check the number of points, so we can simply put these into a list like:

public static List <GeoPoint> decodePoints(String encoded_points){
int index = 0;
int lat = 0;
int lng = 0;
List <GeoPoint> out = new ArrayList<GeoPoint>();

try {
    int shift;
    int result;
    while (index < encoded_points.length()) {
        shift = 0;
        result = 0;
        while (true) {
            int b = encoded_points.charAt(index++) - '?';
            result |= ((b & 31) << shift);
            shift += 5;
            if (b < 32)
                break;
        }
        lat += ((result & 1) != 0 ? ~(result >> 1) : result >> 1);

        shift = 0;
        result = 0;
        while (true) {
            int b = encoded_points.charAt(index++) - '?';
            result |= ((b & 31) << shift);
            shift += 5;
            if (b < 32)
                break;
        }
        lng += ((result & 1) != 0 ? ~(result >> 1) : result >> 1);
        /* Add the new Lat/Lng to the Array. */
        out.add(new GeoPoint((lat*10),(lng*10)));
    }
    return out;
}catch(Exception e) {
    e.printStackTrace();
}
return out;
}

---

编辑：OLD code

---

OLD CODE

public class PolylineDecoder {
/**
 * Transform a encoded PolyLine to a Array of GeoPoints.
 * Java implementation of the original Google JS code.
 * @see Original encoding part: <a href="http://code.google.com/apis/maps/documentation/polylinealgorithm.html">http://code.google.com/apis/maps/documentation/polylinealgorithm.html</a>
 * @return Array of all GeoPoints decoded from the PolyLine-String.
 * @param encoded_points String containing the encoded PolyLine. 
 * @param countExpected Number of points that are encoded in the PolyLine. Easiest way is to use the length of the ZoomLevels-String. 
 * @throws DecodingException 
 */
public static GeoPoint[] decodePoints(String encoded_points, int countExpected){
    int index = 0;
    int lat = 0;
    int lng = 0;
    int cnt = 0;
    GeoPoint[] out = new GeoPoint[countExpected];

    try {
        int shift;
        int result;
        while (index < encoded_points.length()) {
            shift = 0;
            result = 0;
            while (true) {
                int b = encoded_points.charAt(index++) - '?';
                result |= ((b & 31) << shift);
                shift += 5;
                if (b < 32)
                    break;
            }
            lat += ((result & 1) != 0 ? ~(result >> 1) : result >> 1);

            shift = 0;
            result = 0;
            while (true) {
                int b = encoded_points.charAt(index++) - '?';
                result |= ((b & 31) << shift);
                shift += 5;
                if (b < 32)
                    break;
            }
            lng += ((result & 1) != 0 ? ~(result >> 1) : result >> 1);
            /* Add the new Lat/Lng to the Array. */
            out[cnt++] = new GeoPoint((lat*10),(lng*10));
        }
        return out;
    }catch(Exception e) {
        e.printStackTrace();
    }
    return out;
}

public static int[] decodeZoomLevels(String encodedZoomLevels){
    int[] out = new int[encodedZoomLevels.length()];
    int index = 0;

    for(char c : encodedZoomLevels.toCharArray())
        out[index++] = c - '?';
    return out;

}
}

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