java - 尝试检索对象字符串时出现 JSON 异常

Question

我正在尝试从下面的 JSON 中检索“Maxspeed”字符串。它遍历数组，但是当它到达“tag”对象并尝试检索“maxspeed”值时，它返回一个异常(如下)。

有谁知道为什么会这样吗？任何帮助将不胜感激。

谢谢。

异常:

org.json.JSONException: No value for maxspeed

Java:

JSONObject parentObject = new JSONObject(result);

                JSONArray speedJSON = parentObject.getJSONArray("elements"); 

                for (int i = 0; i < speedJSON.length(); i++) {

                    JSONObject element = (JSONObject) speedJSON.get(i);

                    if (!element.isNull("tags")) {
                        //JSONObject tags = (JSONObject) speedJSON.getJSONObject(i).get("tags");
                        String maxspeed = element.getString("maxspeed");
                        txtSpeed.setText(maxspeed+" here");
                    } else {
                        //Your error handling here...
                    }
                }
                //txtSpeed.setText(""+);
                this.progressDialog.dismiss();

JSON:

{
  "version": 0.6,
  "generator": "Overpass API",
  "osm3s": {
    "timestamp_osm_base": "2015-03-16T20:10:02Z",
    "copyright": "The data included in this document is from www.openstreetmap.org. The data is made available under ODbL."
  },
  "elements": [

{
  "type": "node",
  "id": 768053039,
  "lat": 54.9526671,
  "lon": -7.7273348
},
{
  "type": "node",
  "id": 768053040,
  "lat": 54.9498094,
  "lon": -7.7176056
},
{
  "type": "node",
  "id": 768053041,
  "lat": 54.9497066,
  "lon": -7.7173174
},
{
  "type": "node",
  "id": 768053043,
  "lat": 54.9495658,
  "lon": -7.7170937
},
{
  "type": "node",
  "id": 768053044,
  "lat": 54.9495035,
  "lon": -7.7169816
},
{
  "type": "node",
  "id": 791492493,
  "lat": 54.9494183,
  "lon": -7.7168205
},
{
  "type": "node",
  "id": 795319854,
  "lat": 54.9510427,
  "lon": -7.7218262
},
{
  "type": "node",
  "id": 795320324,
  "lat": 54.9509153,
  "lon": -7.7213706
},
{
  "type": "node",
  "id": 1922546572,
  "lat": 54.9502165,
  "lon": -7.7190169
},
{
  "type": "node",
  "id": 1922546679,
  "lat": 54.9504739,
  "lon": -7.7199078
},
{
  "type": "node",
  "id": 1922546692,
  "lat": 54.9500860,
  "lon": -7.7185174
},
{
  "type": "node",
  "id": 1922602861,
  "lat": 54.9517250,
  "lon": -7.7241644
},
{
  "type": "node",
  "id": 1922622063,
  "lat": 54.9514357,
  "lon": -7.7231690
},
{
  "type": "node",
  "id": 2673934802,
  "lat": 54.9498543,
  "lon": -7.7177617
},
{
  "type": "way",
  "id": 64273241,
  "nodes": [
    768053039,
    1922602861,
    1922622063,
    795319854,
    795320324
  ],
  "tags": {
    "highway": "secondary",
    "maxspeed": "60",
    "name": "Port Road",
    "oneway": "no",
    "ref": "R229"
  }
},
{
  "type": "way",
  "id": 64887990,
  "nodes": [
    795320324,
    1922546679,
    1922546572,
    1922546692,
    2673934802,
    768053040,
    768053041,
    768053043,
    768053044,
    791492493
  ],
  "tags": {
    "highway": "secondary",
    "maxspeed": "60",
    "name": "Port Road",
    "oneway": "no",
    "ref": "R229"
  }
}

  ]
}

Answer 1

您试图从元素获取最大速度，但它不存在。它位于 element 中的 tags 对象内。

你需要这样的东西

if (!element.isNull("tags")) {
    JSONObject tags = element.getJSONObject("tags");
    String maxspeed = tags.getString("maxspeed");
    txtSpeed.setText(maxspeed+" here");
} else {
    //Your error handling here...
}