当我运行我的代码时显示消息很遗憾您的应用已关闭。这是在ProgressDialog解雇后开始发生的。
我认为这里的错误[Searchresult.java]
@Override
protected void onPostExecute(Void args) {
// Locate the listview in listview_main.xml
// Pass the results into ListViewAdapter.java
adapter = new ListViewAdapter(Searchresult.this, arraylist);
// Set the adapter to the ListView
listview.setAdapter(adapter);
// Close the progressdialog
mProgressDialog.dismiss();
}
这是我的日志猫
Shutting down VM
06-30 05:08:03.882 23680-23680/com.ali.test E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.ali.test, PID: 23680
java.lang.NullPointerException: Attempt to invoke virtual method 'org.json.JSONArray org.json.JSONObject.getJSONArray(java.lang.String)' on a null object reference
at com.ali.test.Searchresult$DownloadJSON.onPostExecute(Searchresult.java:93)
at com.ali.test.Searchresult$DownloadJSON.onPostExecute(Searchresult.java:54)
at android.os.AsyncTask.finish(AsyncTask.java:651)
at android.os.AsyncTask.-wrap1(AsyncTask.java)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
06-30 05:08:03.884 1768-2143/system_process W/ActivityManager: Force finishing activity com.ali.test/.Searchresult
home.jave [主档案]
public class home extends AppCompatActivity {
EditText search_txt;
Button search_btn;
String strbook;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
search_txt = (EditText) findViewById(R.id.editText);
search_btn = (Button) findViewById(R.id.button);
search_btn.setOnClickListener(listener);
search_txt.setOnKeyListener(new View.OnKeyListener() {
public boolean onKey(View v, int keyCode, KeyEvent event) {
// If the event is a key-down event on the "enter" button
if ((event.getAction() == KeyEvent.ACTION_DOWN) &&
(keyCode == KeyEvent.KEYCODE_ENTER)) {
// Perform action on key press
search_btn.setOnClickListener(listener);
return true;
}
return false;
}
});
}private OnClickListener listener = new OnClickListener() {
@Override
public void onClick(View v) {
strbook = search_txt.getText().toString();
if (TextUtils.isEmpty(strbook))
{
search_txt.setError("Enter name");
}
else {
Intent i = new Intent(home.this, Searchresult.class);
startActivity(i);
}
}
};
}
ListViewAdapter.java
public class ListViewAdapter extends BaseAdapter {
// Declare Variables
Context context;
LayoutInflater inflater;
ArrayList<HashMap<String, String>> data;
ImageLoader imageLoader;
HashMap<String, String> resultp = new HashMap<String, String>();
public ListViewAdapter(Context context,
ArrayList<HashMap<String, String>> arraylist) {
this.context = context;
data = arraylist;
imageLoader = new ImageLoader(context);
}
@Override
public int getCount() {
return data.size();
}
@Override
public Object getItem(int position) {
return null;
}
@Override
public long getItemId(int position) {
return 0;
}
public View getView(final int position, View convertView, ViewGroup parent) {
// Declare Variables
TextView rank;
ImageView flag;
inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View itemView = inflater.inflate(R.layout.list_item, parent, false);
// Get the position
resultp = data.get(position);
// Locate the TextViews in listview_item.xml
rank = (TextView) itemView.findViewById(R.id.rank);
// Locate the ImageView in listview_item.xml
flag = (ImageView) itemView.findViewById(R.id.flag);
// Capture position and set results to the TextViews
rank.setText(resultp.get(Searchresult.RANK));
// Capture position and set results to the ImageView
// Passes flag images URL into ImageLoader.class
imageLoader.DisplayImage(resultp.get(Searchresult.FLAG), flag);
// Capture ListView item click
itemView.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
// Get the position
resultp = data.get(position);
Intent intent = new Intent(context,SingleItemView.class);
// Pass all data rank
intent.putExtra("rank", resultp.get(Searchresult.RANK));
// Pass all data flag
intent.putExtra("flag", resultp.get(Searchresult.FLAG));
// Start SingleItemView Class
context.startActivity(intent);
}
});
return itemView;
}
}
searchresult.java
public class Searchresult extends AppCompatActivity {
// Declare Variables
JSONObject jsonobject;
JSONArray jsonarray;
ListView listview;
ListViewAdapter adapter;
ProgressDialog mProgressDialog;
ArrayList<HashMap<String, String>> arraylist;
static String RANK = "rank";
static String FLAG = "flag";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
listview = (ListView) findViewById(R.id.list);
// Get the view from listview_main.xml
setContentView(R.layout.list_item);
// Execute DownloadJSON AsyncTask
new DownloadJSON().execute();
}
// DownloadJSON AsyncTask
private class DownloadJSON extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
// Create a progressdialog
mProgressDialog = new ProgressDialog(Searchresult.this);
// Set progressdialog title
// mProgressDialog.setTitle("Android JSON Parse Tutorial");
// Set progressdialog message
mProgressDialog.setMessage("Loading...");
mProgressDialog.setIndeterminate(false);
// Show progressdialog
mProgressDialog.show();
}
@Override
protected Void doInBackground(Void... params) {
// Create an array
arraylist = new ArrayList<HashMap<String, String>>();
// Retrieve JSON Objects from the given URL address
jsonobject = JSONfunctions
.getJSONfromURL("http://www.androidbegin.com/tutorial/jsonparsetutorial.txt");
try {
// Locate the array name in JSON
jsonarray = jsonobject.getJSONArray("worldpopulation");
for (int i = 0; i < jsonarray.length(); i++) {
HashMap<String, String> map = new HashMap<String, String>();
jsonobject = jsonarray.getJSONObject(i);
// Retrive JSON Objects
map.put("rank", jsonobject.getString("rank"));
map.put("flag", jsonobject.getString("flag"));
// Set the JSON Objects into the array
arraylist.add(map);
}
} catch (JSONException e) {
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void args) {
// Locate the listview in listview_main.xml
// Pass the results into ListViewAdapter.java
adapter = new ListViewAdapter(Searchresult.this, arraylist);
// Set the adapter to the ListView
listview.setAdapter(adapter);
// Close the progressdialog
mProgressDialog.dismiss();
}
}
}
答案 0 :(得分：0)
确保返回的json是您期望的那个。所以在之前的状态，检查你确实有一个jsonobject，然后检查是否有一个带有预期名称的jsonarray，并查看模式。
您可以查看一下Retrofit库，它对于RESTful服务调用来说非常棒。 http://square.github.io/retrofit/
虽然学习曲线很小。