无法在 AsyncTask 的 onPostExecute 中解析构造函数 ArrayAdapter

Question

我知道这听起来像是一个重复的问题，但我已经尝试了所有的解决方案都没有 works.It 显示错误 "Cannot resolve constructor ArrayAdapter" 我在 Mainactivity 中有列表视图，我已经通过了第二个 activity 我正在搜索远程数据库并在列表视图中显示结果。看看。。谢谢。。这是主要的activity:

public class Main2Activity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
private EditText location;
private TextView result ;
ListView lv;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    location = (EditText)findViewById(R.id.editText1);
    result = (TextView)findViewById(R.id.textView4);
    lv = (ListView) findViewById( R.id.lv );
 }
 public void search(View view){
    String slocation = location.getText().toString();
    new SearchActivity(this,lv,1).execute(slocation);
}

搜索活动

public class SearchActivity extends AsyncTask<String,Void,String[]>{
private Context context;
private int byGetOrPost = 0;
private TextView sresult;
ListView lv1;
JSONArray garages;
String[] names;

public SearchActivity(Context context,ListView lv1,int flag) {
    this.context = context;
    byGetOrPost = flag;
    this.lv1 = lv1;
}

protected void onPreExecute(){

}

@Override
protected String[] doInBackground(String... arg0) {
        try{
            String location = (String)arg0[0];

            String link="http://garagekhojo.in/androidtest.php";
            String data  = URLEncoder.encode("location", "UTF-8") + "=" + URLEncoder.encode(location, "UTF-8");

            URL url = new URL(link);
            URLConnection conn = url.openConnection();

            conn.setDoOutput(true);
            OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream());

            wr.write( data );
            wr.flush();

            BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));

            StringBuilder sb = new StringBuilder();
            String line = null;

            // Read Server Response
            while((line = reader.readLine()) != null)
            {
                sb.append(line);
                break;
            }

            String newsb = sb.toString();
            JSONObject jo = new JSONObject(newsb) ;
            garages = jo.getJSONArray("garages");
            for (int i = 0; i < garages.length(); i++) {
                JSONObject c = garages.getJSONObject(i);

                names[i] = c.getString("name");
            }
            return names;


        }
        catch(Exception e){
            return null;
        }

}

@Override
protected void onPostExecute(String[] names){
    ArrayAdapter<String> adapter;
    adapter = new ArrayAdapter<String>(this, R.layout.class,names);
    lv1.setAdapter(adapter);
}

}

Answer 1

请将 activity 的 Context 传递给异步任务并用它代替

 adapter = new ArrayAdapter<String>(context, R.layout.class,names);

上下文来自 this.context = context;

永远不要使用 Activity 作为 AsyncTask 的后缀（不好的做法）（而不是 SearchActivity 使用 SearchAsyncTask）

Answer 2

您必须编辑 SearchActivity.java。首先将其命名为 SearchAsyncTask。你还没有初始化 name[] 字符串数组，这就是它抛出空指针异常的原因。

这里是SearchAsyncTask.java

的代码

public class SearchAsyncTask extends AsyncTask<String,Void,String[]>{
private Context context;
private int byGetOrPost = 0;
private TextView sresult;
ListView lv1;
JSONArray garages;

public SearchActivity(Context context,ListView lv1,int flag) {
   this.context = context;
   byGetOrPost = flag;
   this.lv1 = lv1;
}

protected void onPreExecute(){

}

@Override
protected String[] doInBackground(String... arg0) {
     try{
        String location = (String)arg0[0];

        String link="http://garagekhojo.in/androidtest.php";
        String data  = URLEncoder.encode("location", "UTF-8") + "=" + URLEncoder.encode(location, "UTF-8");

        URL url = new URL(link);
        URLConnection conn = url.openConnection();

        conn.setDoOutput(true);
        OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream());

        wr.write( data );
        wr.flush();

        BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));

        StringBuilder sb = new StringBuilder();
        String line = null;

        // Read Server Response
        while((line = reader.readLine()) != null)
        {
            sb.append(line);
            break;
        }

        String newsb = sb.toString();
        JSONObject jo = new JSONObject(newsb) ;
        garages = jo.getJSONArray("garages");
        String[] names = new String[garages.length()];
        for (int i = 0; i < garages.length(); i++) {
            JSONObject c = garages.getJSONObject(i);
            names[i] = c.getString("name");
        }
        return names;
    }
    catch(Exception e){
        return null;
    }
}

@Override
protected void onPostExecute(String[] names){
    if(names!=null){
       ArrayAdapter<String> adapter;
       adapter = new ArrayAdapter<String>(context, R.layout.class,names);
       lv1.setAdapter(adapter);
    }
}

您也应该应用 null 检查，因为在异常情况下您将返回 null 作为值。因此，如果再次发生任何异常，它就会崩溃。也没有必要定义全局变量 String[] 名称，因为您没有使用该变量。我也编辑了 class 和 class 的名称。请检查。

无法在 AsyncTask 的 onPostExecute 中解析构造函数 ArrayAdapter

Cannot resolve constructor ArrayAdapter in onPostExecute in AsyncTask

android

listview

android-arrayadapter

android-asynctask