无法解析 AsyncTask 中 onPostExecute 中的构造函数 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解决方案，但没有任何效果。它显示错误“无法解析构造函数 ArrayAdapter”我在 Mainactivity 中有列表视图，我已将其传递给我正在搜索的第二个活动远程数据库并在列表视图中显示结果。 看看。。谢谢。。 这是主要活动：

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

您必须编辑您的 SearchActivity.java。首先将其命名为 SearchAsyncTask。您尚未初始化 name[] 字符串数组，这不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。所以如果发生任何异常，它就会崩溃。此外，由于您没有使用该变量，因此无需定义全局变量 String[] 名称。我也编辑了班级和班级名称。请检查。

Answer 2

请将活动的上下文传递给异步任务并代替它使用

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

上下文来自this.context = context;

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