为什么我的Android应用程序无法从JSON url获取数据？

Question

我正在尝试运行基于WorlBank API的应用程序.我有一个JSON URL来获取有关某个国家/地区的数据,然后在TextViews中显示它.简单.但只要我关闭运行应用程序.

这是我的文件:

主要活动:

public class MainActivity extends Activity {

//URL to get JSON Array
private static String url = "http://api.worldbank.org/countries/ir?format=json";

//JSON node Names
private static final String PAGE = "page";
private static final String VALUE = "value";
private static final String NAME = "name";
private static final String GEO = "region";

JSONArray page = null;

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

    //Creating new JSON Parser
    JSONParser jParser = new JSONParser();
    // Getting JSON from URL
    JSONObject json = jParser.getJSONFromUrl(url);

    try{
        //Getting JSON Array
        page = json.getJSONArray(PAGE);
        JSONObject c = page.getJSONObject(0);

        //Sorting JSON item in a Variable
        String value = c.getString(VALUE);
        String name = c.getString(NAME);
        String geo = c.getString(GEO);

        //Importing to TextView
        final TextView id1 = (TextView) findViewById(R.id.id);
        final TextView name1 = (TextView) findViewById(R.id.name);
        final TextView geo1 = (TextView) findViewById(R.id.geo);

        //set JSON Data in TextView
        id1.setText(value);
        name1.setText(name);
        geo1.setText(geo);
    } catch (JSONException e){
        e.printStackTrace();
    }



}

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

    }

JSONParser:

public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";

// constructor
public JSONParser() {

}

public JSONObject getJSONFromUrl(String url) {

    // Making HTTP request
    try {
        // defaultHttpClient
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);

        HttpResponse httpResponse = httpClient.execute(httpPost);
        HttpEntity httpEntity = httpResponse.getEntity();
        is = httpEntity.getContent();           

    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        json = sb.toString();
    } catch (Exception e) {
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }

    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }

    // return JSON String
    return jObj;

}
}

XML:

<TextView
    android:id="@+id/id"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/name"
    android:textAppearance="?android:attr/textAppearanceLarge" />

<TextView
    android:id="@+id/name"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/id"
    android:textAppearance="?android:attr/textAppearanceLarge" />

<TextView
    android:id="@+id/geo"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/id"
    android:layout_alignParentTop="true"
    android:layout_marginTop="76dp"
    android:textAppearance="?android:attr/textAppearanceLarge" />

任何的想法？

世界银行api:http: //data.worldbank.org/node/18

更新:

机器人:的minSdkVersion = "8"

机器人:targetSdkVersion = "18"

FATAL EXCEPTION: main
E/AndroidRuntime(966): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jsonsyctask/com.example.jsonsyctask.Main}: android.os.NetworkOnMainThreadException
E/AndroidRuntime(966):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
E/AndroidRuntime(966):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
E/AndroidRuntime(966):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
E/AndroidRuntime(966):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
E/AndroidRuntime(966):  at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(966):  at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(966):  at android.app.ActivityThread.main(ActivityThread.java:5103)
E/AndroidRuntime(966):  at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(966):  at java.lang.reflect.Method.invoke(Method.java:525)
E/AndroidRuntime(966):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)

Answer 1

问题正在发生,因为您正在尝试在UI线程上执行网络操作.您需要使用后台线程进行网络操作.

使用AsyncTask如下:

public class MainActivity extends Activity {

    //URL to get JSON Array
    private static String url = "http://api.worldbank.org/countries/ir?format=json";

    //JSON node Names
    private static final String PAGE = "page";
    private static final String VALUE = "value";
    private static final String NAME = "name";
    private static final String GEO = "region";

    JSONArray page = null;

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

        new GetJSONTask().execute(url);

        // do not parse here..
        ...
        ...
    }
    ...
    ...

    class GetJSONTask extends AsyncTask<String, Void, JSONObject> {


        protected JSONObject doInBackground(String... urls) {
            try {
                JSONParser jParser = new JSONParser();
                return jParser.getJSONFromUrl(urls[0]);
            } catch (Exception e) {
                return null;
            }
        }

        protected void onPostExecute(JSONObject json) {
            // do all the parsing here:
            try {
                //Getting JSON Array
                page = json.getJSONArray(PAGE);
                JSONObject c = page.getJSONObject(0);

                //Sorting JSON item in a Variable
                String value = c.getString(VALUE);
                String name = c.getString(NAME);
                String geo = c.getString(GEO);

                //Importing to TextView
                final TextView id1 = (TextView) findViewById(R.id.id);
                final TextView name1 = (TextView) findViewById(R.id.name);
                final TextView geo1 = (TextView) findViewById(R.id.geo);

                //set JSON Data in TextView
                id1.setText(value);
                name1.setText(name);
                geo1.setText(geo);
            }
            catch (JSONException e)
            {
                e.printStackTrace();
            }
        } 
    }
}

参考:http://developer.android.com/reference/android/os/AsyncTask.html

更新发现的另一个错误,更新XML

<TextView
    android:id="@+id/id"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/name"
    android:textAppearance="?android:attr/textAppearanceLarge" />

<TextView
    android:id="@+id/name"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge" />
...
...

你不能有两个观点说A below B,B below A那会导致问题!