Question

我的json看起来像这样：

{"type":"FeatureCollection","metadata":{"generated":1428783374000,"url":"http://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&starttime=2015-04-04&endtime=2015-04-05","title":"USGS Earthquakes","status":200,"api":"1.0.17","count":328},"features":[{"type":"Feature","properties":{"mag":1.3,"place":"8km SSE of Talmage, California","time":1428191575500,"updated":1428359465102,"tz":-420,"url":"http://earthquake.usgs.gov/earthquakes/eventpage/nc72426686","detail":"http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=nc72426686&format=geojson","felt":null,"cdi":null,"mmi":null,"alert":null,"status":"reviewed","tsunami":0,"sig":26,"net":"nc","code":"72426686","ids":",nc72426686,","sources":",nc,","types":",cap,general-link,geoserve,nearby-cities,origin,phase-data,scitech-link,tectonic-summary,","nst":12,"dmin":0.08508,"rms":0.06,"gap":154,"magType":"md","type":"earthquake","title":"M 1.3 - 8km SSE of Talmage, California"},"geometry":{"type":"Point","coordinates":[-123.1233333,39.0688333,7.27]},"id":"nc72426686"},

我的主要活动代码如下所示：

public class MainActivity extends ActionBarActivity {

private static final String LOG_TAG ="JSON STRING";
TextView httpData;
HttpClient client;
JSONObject json;


final static String URL = "http://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&starttime=2015-04-04&endtime=2015-04-05";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    httpData = (TextView) findViewById(R.id.tvHttp);
    client = new DefaultHttpClient();

    new Read().execute("features");

}

public JSONObject lastEvent(String event) throws ClientProtocolException, IOException, JSONException {
    StringBuilder url = new StringBuilder(URL);

    HttpGet get = new HttpGet(url.toString());
    HttpResponse response = client.execute(get);

    int status = response.getStatusLine().getStatusCode();

    if ( status == 200 ) {
        HttpEntity entity = response.getEntity();
        String data = EntityUtils.toString(entity);
        JSONArray timeline = new JSONArray(data);
        JSONObject last = timeline.getJSONObject(0);

        return last;
    }
    else {
        Toast.makeText(MainActivity.this, "error", Toast.LENGTH_SHORT);
        return null;
    }
}


public class Read extends AsyncTask<String, Integer, String> {

    @Override
    protected String doInBackground(String... params) {
        try {
            json = lastEvent("title");
            return json.getString(params[0]);

        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(String result ) {
       httpData.setText(result);
    }
}

public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

}

我的activity_main.xml如下所示：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="wrap_content"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">
<ScrollView android:layout_height="fill_parent" android:layout_width="fill_parent">
<TextView android:text="Loading Data" android:id="@+id/tvHttp" android:layout_width="wrap_content"
    android:layout_height="wrap_content" />
</ScrollView>

我正在努力获得＆＃39; title＆＃39;从JSONArray的第一个元素，但我得到一个空白的文本视图屏幕。我对Java和Android有点新手，所以如果我更容易使用不同的格式（例如XML），我也可以尝试。任何见解或提示都非常感谢。

Answer 1

好的，假设我们有你发布的JSON

{"type":"FeatureCollection","metadata":{"generated":1428783374000,"url":"http://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&starttime=2015-04-04&endtime=2015-04-05","title":"USGS Earthquakes","status":200,"api":"1.0.17","count":328},"features":[{"type":"Feature","properties":{"mag":1.3,"place":"8km SSE of Talmage, California","time":1428191575500,"updated":1428359465102,"tz":-420,"url":"http://earthquake.usgs.gov/earthquakes/eventpage/nc72426686","detail":"http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=nc72426686&format=geojson","felt":null,"cdi":null,"mmi":null,"alert":null,"status":"reviewed","tsunami":0,"sig":26,"net":"nc","code":"72426686","ids":",nc72426686,","sources":",nc,","types":",cap,general-link,geoserve,nearby-cities,origin,phase-data,scitech-link,tectonic-summary,","nst":12,"dmin":0.08508,"rms":0.06,"gap":154,"magType":"md","type":"earthquake","title":"M 1.3 - 8km SSE of Talmage, California"},"geometry":{"type":"Point","coordinates":[-123.1233333,39.0688333,7.27]},"id":"nc72426686"},

这是一个object。我们想要进入键features中的数组，并且我们希望在该数组的第一个元素（它是一个对象）中使用标题键。

查看您的lastEvent功能。您传递一个名为event的字符串。但这从未使用过。

public String lastEvent(String event) throws ClientProtocolException, IOException, JSONException {
    StringBuilder url = new StringBuilder(URL);

    HttpGet get = new HttpGet(url.toString());
    HttpResponse response = client.execute(get);

    int status = response.getStatusLine().getStatusCode();

    if ( status == 200 ) {
        HttpEntity entity = response.getEntity();
        String data = EntityUtils.toString(entity);
        // data now contains the json object I posted above
        // So we fetch it
        JSONObject timeline = new JSONObject(data);
        // We want the features array
        JSONArray features = timeline.getJSONArray("features");
        // The first element
        JSONObject first = timeline.getJSONObject(0);
        // The titles attribute. I assume lastEvent("titles")
        // is the way you call this function
        String last = first.getString(event);

        return last;
    }
    else {
        Toast.makeText(MainActivity.this, "error", Toast.LENGTH_SHORT);
        return null;
    }
}

注意我更改了lastEvent的返回类型，因为我们从对象中获取了一个String。第一个参数event现在是我们想要得到的字段，我认为这是你的意图，因为你在AsyncTask中称之为。

另外，检查你的Logcat！可能会抛出JSONException，您捕获并打印其消息并返回null。返回null，稍后调用httpData.setText(null)将导致空TextView

修改：您的doInBackground功能也不需要再次调用getString() lastEvent的返回值。我不知道你的AsyncTask需要多么通用。但是我写的代码可能会帮助你达到你想要的目标。

来自JSON Object的Android显示值

1 个答案: