Question

首先，我将解释我正在尝试使用我的Android应用程序。该应用程序允许用户输入他们的车辆信息以及起点和终点。然后，用户将点击“计划我的公路旅行”按钮，该按钮将把它们发送到第二页上有Google Map的页面。在第二页上，应用程序将获取原点和目的地，将它们放入Google Directions URL，即

http://maps.googleapis.com/maps/api/directions/json?origin=90210&destination=02115&sensor=false&units=imperial

然后将“overview_polyline”JSONObject解析为LatLng ArrayList。该ArrayList将用于使用折线绘制原点和目的地之间的路径。

正如您在屏幕截图中看到的那样，用户有4个微调器可供选择，与此问题无关。用户还有一个Origin EditText框和一个我上面提到的Destination EditText框。

enter image description here

我的问题如下。当我单击将我带到第二页的按钮时，应用程序崩溃了。它甚至没有超过setContentView(R.layout.page2);。我已经在另一个项目中测试了JSON解析，并且解析代码没有任何问题，但由于某种原因它在这种情况下不起作用。我也在使用AsyncTask类。这是要走的路吗？如果没有，是否可以展示一个正确的方法来做这个例子？此外，正如您将在代码中看到的那样，如果我手动将点添加到ArrayList而不是动态填充，则加载地图并使折线工作。

这是代码......

Page2Activity.java

 public class Page2Activity extends FragmentActivity {

GoogleMap map;
//Non Dynamic ArrayList
//ArrayList<LatLng> points = new ArrayList<LatLng>();

//Dynamic ArrayList
ArrayList<LatLng> poly = new ArrayList<LatLng>();

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.page2);

    //Async Task here
    new populatePolys().execute();


    //This works if I manually add the points. Non Dynamic. But obviously this is not what I want.

//      SupportMapFragment fm = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
//      map = fm.getMap();
//       
//      points.add(new LatLng(51.5, -0.1));
//      points.add(new LatLng(40.7, -74.0));
//      points.add(new LatLng(30.2, -80.1));
//      Polyline line = map.addPolyline(new PolylineOptions()
//      .addAll(points)
//      .width(5)
//      .color(Color.RED));
}

 class populatePolys extends AsyncTask<Void, Void, ArrayList<LatLng>> {
    protected ArrayList<LatLng> doInBackground(Void... params) {

        //Creating a new instance of the Activity for the first page
        //The first page holds the user's input for the Origin EditText box and Destination EditText box.
        MainActivity mA = new MainActivity();
        String pointA = "";
        String pointB = "";
        try {
            //Grabbing the user input from the main page.
            pointA = URLEncoder.encode(mA.originEditText.getText().toString(), "UTF-8");
            pointB = URLEncoder.encode(mA.destinationEditText.getText().toString(), "UTF-8");
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }

        JSONObject jsonObject = null;
        String status = "INVALID_REQUEST";

        try {
            jsonObject = readJsonFromUrl("http://maps.googleapis.com/maps/api/directions/json?origin=" + pointA + "&destination=" + pointB + "&sensor=false&units=imperial");
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }

        if(status.equals("OK")){
            //Directions entered are correct.
            JSONObject polyArray;
            JSONArray routesArray;
            try {
                //Grabbing the Polyline points String. This does pull the correct value.
                //Parsing is correct.
                routesArray = jsonObject.getJSONArray("routes");
                JSONObject route = routesArray.getJSONObject(0);
                polyArray = route.getJSONObject("overview_polyline");
                String polyPoints = polyArray.getString("points");

                //Passing the Polyline points from the JSON file I get from the Google Directions URL into a decoder.
                decodePoly(polyPoints);
            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return poly;
    }

    protected void onPostExecute(NodeList makeList) {

        //Adding the Dynamic ArrayList "poly" into Polylines.

        SupportMapFragment fm = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
        map = fm.getMap();

        Polyline line = map.addPolyline(new PolylineOptions()
        .addAll(poly)
        .width(5)
        .color(Color.RED));

    }


}


/*
 * LatLng Decoder for polyline
 */

private List<LatLng> decodePoly(String encoded) {

    int index = 0, len = encoded.length();
    int lat = 0, lng = 0;

    while (index < len) {
        int b, shift = 0, result = 0;
        do {
            b = encoded.charAt(index++) - 63;
            result |= (b & 0x1f) << shift;
            shift += 5;
        } while (b >= 0x20);
        int dlat = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
        lat += dlat;

        shift = 0;
        result = 0;
        do {
            b = encoded.charAt(index++) - 63;
            result |= (b & 0x1f) << shift;
            shift += 5;
        } while (b >= 0x20);
        int dlng = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
        lng += dlng;

        LatLng p = new LatLng((int) (((double) lat / 1E5) * 1E6),
             (int) (((double) lng / 1E5) * 1E6));
        poly.add(p);
    }

    return poly;
}

/*
 * Methods to parse the JSON when grabbing from Google Directions API
 */

private static String readAll(Reader rd) throws IOException {
    StringBuilder sb = new StringBuilder();
    int cp;
    while ((cp = rd.read()) != -1) {
      sb.append((char) cp);
    }
    return sb.toString();
}

public static JSONObject readJsonFromUrl(String url) throws IOException, JSONException {

      InputStream is = new URL(url).openStream();
        try {
          BufferedReader rd = new BufferedReader(new InputStreamReader(is, Charset.forName("UTF-8")));
          String jsonText = readAll(rd);
          JSONObject jsonObject = new JSONObject(jsonText);
          return jsonObject;
        } finally {
          is.close();
        }   
  }



}

page2.xml的代码.... 更新（请参阅旧代码的编辑）

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
    <fragment
    android:id="@+id/map"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    class="com.google.android.gms.maps.SupportMapFragment"/>
</LinearLayout>

更新了LogCat ......

07-10 11:33:09.193: E/AndroidRuntime(8130): FATAL EXCEPTION: AsyncTask #5
07-10 11:33:09.193: E/AndroidRuntime(8130): java.lang.RuntimeException: An error occured while executing doInBackground()
07-10 11:33:09.193: E/AndroidRuntime(8130):     at android.os.AsyncTask$3.done(AsyncTask.java:299)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at java.lang.Thread.run(Thread.java:856)
07-10 11:33:09.193: E/AndroidRuntime(8130): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
07-10 11:33:09.193: E/AndroidRuntime(8130):     at android.os.Handler.<init>(Handler.java:121)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at android.app.Activity.<init>(Activity.java:763)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at com.example.roadtripplanner.MainActivity.<init>(MainActivity.java:51)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at com.example.roadtripplanner.Page2Activity$populatePolys.doInBackground(Page2Activity.java:74)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at com.example.roadtripplanner.Page2Activity$populatePolys.doInBackground(Page2Activity.java:1)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at android.os.AsyncTask$2.call(AsyncTask.java:287)
07-10 11:33:09.193: E/AndroidRuntime(8130):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
07-10 11:33:09.193: E/AndroidRuntime(8130):     ... 5 more

要查看旧的logcat，请参阅编辑

请询问您是否需要更多代码。

Answer 1

请仔细查看错误Caused by: java.lang.ClassCastException: com.google.android.gms.maps.MapFragment cannot be cast to android.support.v4.app.Fragment

我相信你在xml中使用了错误的类

android:name="com.google.android.gms.maps.MapFragment"

应该是

android:name="com.google.android.gms.maps.SupportMapFragment"

无法使用动态LatLng ArrayList在Android Google地图上绘制折线

1 个答案: