单击按钮后未显示Listview

Question

我正在尝试从stackexchange api获取数据，但是在单击按钮以调用asynctask之后，listview没有填充。没有崩溃

我已经用Listview创建了一个简单的Custom Adapter来填充listview。

MainActivity.java

 button.addEventListener("click", event => {
        event.target.innerText = "In Cart";
        event.target.disabled = true;
        // get product from products
        let cartItem = {
          ...Storage.getProduct(id),
          amount: 1
        };

activity_main.xml

public class MainActivity extends AppCompatActivity {
    private EditText stackSearch;
    private Button searchBtn;
    private String text;
    private static final String BASE_URL = "https://api.stackexchange.com/2.2/questions";
    private StackAsyncTask stackAsyncTask;
    private ArrayList<Questions> stackArrayList;
    private String exception;
    private ListView questionList;
    private StackAdapter stackAdapter;
    //private ProgressBar progressBar;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        stackAsyncTask = new StackAsyncTask();
        stackSearch = findViewById(R.id.book_genre);
        searchBtn = findViewById(R.id.btn_search);
        questionList = findViewById(R.id.book_list);
        stackArrayList = new ArrayList<>();
      //  progressBar = findViewById(R.id.progressBar);

        searchBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.i("kunal","clicked");
                text = stackSearch.getText().toString();
        //        progressBar.setVisibility(View.VISIBLE);
                stackAsyncTask.execute();

            }
        });
    }

    class StackAsyncTask extends AsyncTask<Void,Void,Void> {
        @Override
        protected Void doInBackground(Void... voids) {
            Uri uri = Uri.parse(BASE_URL).buildUpon()
                    .appendQueryParameter("order","desc")
                    .appendQueryParameter("sort","activity")
                    .appendQueryParameter("tagged",text)
                    .appendQueryParameter("site","stackoverflow")
                    .build();
            URL url;
            try {
                url = new URL(uri.toString());
                HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection() ;
                httpURLConnection.connect();
                InputStream inputStream = httpURLConnection.getInputStream();
                InputStreamReader inputStreamReader = new InputStreamReader(inputStream, Charset.forName("UTF-8"));
                BufferedReader reader = new BufferedReader(inputStreamReader);
                StringBuilder buffer = new StringBuilder();
                String line = reader.readLine();
                while(line != null){
                    buffer.append(line);
                    line = reader.readLine();
                }
                JSONObject questions = new JSONObject(buffer.toString());
                JSONArray items = questions.getJSONArray("items");
                for(int i=0;i<20;i++) {
                    JSONObject first = items.getJSONObject(i);
                    JSONObject owner = first.getJSONObject("owner");
                    String profile_image = owner.getString("profile_image");
                    String display_name = owner.getString("display_name");
                    String view_count = first.getString("view_count");
                    String answer_count = first.getString("answer_count");
                    String score = first.getString("score");
                    String last_activity_date = first.getString("last_activity_date");
                    String creation_date = first.getString("creation_date");
                    String link = first.getString("link");
                    String title = first.getString("title");
                    stackArrayList.add(new Questions(display_name, title, link, profile_image, view_count, answer_count, last_activity_date, creation_date, score));
                }
                stackAdapter = new StackAdapter(MainActivity.this,R.layout.questionlistitem, stackArrayList);
                questionList.setAdapter(stackAdapter);
            }catch (Exception e){
                exception = e.toString();
            }
            return null;
        }
    }
}

questionslistitem.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/book_genre"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="@string/query"
        android:inputType="text" />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/btn_search"
        android:layout_gravity="center_horizontal"
        android:text="Search"/>

    <ListView
        android:id="@+id/book_list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>


</LinearLayout>

Questions.java

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/title"
        android:textAppearance="@style/Base.TextAppearance.AppCompat.Large"
        android:textColor="#000"/>

    <LinearLayout
        android:id="@+id/user_stats"
        android:orientation="horizontal"
        android:layout_below="@+id/title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/image"
            android:layout_weight="1"
            android:contentDescription="@string/profile_image"/>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/name"
            android:layout_weight="1"
            android:textAppearance="@style/Base.TextAppearance.AppCompat.Medium"/>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/link"
            android:layout_weight="1"/>

    </LinearLayout>

    <LinearLayout
        android:orientation="horizontal"
        android:layout_below="@+id/user_stats"
        android:id="@+id/views_stats"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:layout_weight="1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/view_count"
            android:text="@string/views"
            android:textAppearance="@style/Base.TextAppearance.AppCompat.Small"/>

        <TextView
            android:layout_weight="1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/answers_count"
            android:text="@string/answers"
            android:textAppearance="@style/Base.TextAppearance.AppCompat.Small"/>

        <TextView
            android:layout_weight="1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/score"
            android:text="@string/score"
            android:textAppearance="@style/Base.TextAppearance.AppCompat.Small"/>
    </LinearLayout>

    <LinearLayout
        android:orientation="horizontal"
        android:id="@+id/dates_stats"
        android:layout_below="@+id/views_stats"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:layout_weight="1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/last_date"
            android:text="@string/last_date"
            android:textAppearance="@style/Base.TextAppearance.AppCompat.Small"/>

        <TextView
            android:layout_weight="1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/creation_date"
            android:text="@string/creation_date"
            android:textAppearance="@style/Base.TextAppearance.AppCompat.Small"/>

    </LinearLayout>

</RelativeLayout>

StackAdapter.java

public class Questions{

    private String owner;

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    private String title;
    private String link;
    private String image;
    private String view_count;
    private String answer_count;
    private String last_activity;
    private String creation;
    private String score;

    public Questions(String owner, String title, String link, String image, String view_count, String answer_count, String last_activity, String creation, String score) {
        this.owner = owner;
        this.title = title;
        this.link = link;
        this.image = image;
        this.view_count = view_count;
        this.answer_count = answer_count;
        this.last_activity = last_activity;
        this.creation = creation;
        this.score = score;
    }

    public String getOwner() {
        return owner;
    }

    public void setOwner(String owner) {
        this.owner = owner;
    }

    public String getLink() {
        return link;
    }

    public void setLink(String link) {
        this.link = link;
    }

    public String getImage() {
        return image;
    }

    public void setImage(String image) {
        this.image = image;
    }

    public String getView_count() {
        return view_count;
    }

    public void setView_count(String view_count) {
        this.view_count = view_count;
    }

    public String getAnswer_count() {
        return answer_count;
    }

    public void setAnswer_count(String answer_count) {
        this.answer_count = answer_count;
    }

    public String getLast_activity() {
        return last_activity;
    }

    public void setLast_activity(String last_activity) {
        this.last_activity = last_activity;
    }

    public String getCreation() {
        return creation;
    }

    public void setCreation(String creation) {
        this.creation = creation;
    }

    public String getScore() {
        return score;
    }

    public void setScore(String score) {
        this.score = score;
    }
}

我尝试只用字符串填充listvie，但是它没有用，所以这不是api提取的问题。谢谢。

修改

public class StackAdapter extends ArrayAdapter {

    private int resourceLayout;
    private Context mContext;

    public StackAdapter(Context context, int resource,List objects) {
        super(context, resource, objects);
        this.resourceLayout = resource;
        this.mContext = context;
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        View v = convertView;
        if (v == null) {
            LayoutInflater vi;
            vi = LayoutInflater.from(mContext);
            v = vi.inflate(resourceLayout, null);
        }

        Questions questions = (Questions) getItem(position);

        TextView title = v.findViewById(R.id.title);
        TextView views = v.findViewById(R.id.view_count);
        TextView score = v.findViewById(R.id.score);
        TextView answers = v.findViewById(R.id.answers_count);
        TextView author = v.findViewById(R.id.name);
        TextView last = v.findViewById(R.id.last_date);
        TextView creation = v.findViewById(R.id.creation_date);
        TextView link = v.findViewById(R.id.link);
        ImageView image = v.findViewById(R.id.image);


        title.append(questions.getTitle());
        views.append(questions.getView_count());
        score.append(questions.getScore());
        answers.append(questions.getAnswer_count());
        author.append(questions.getOwner());
        last.append(questions.getLast_activity());
        creation.append(questions.getCreation());
        link.append(questions.getLink());
        try {
            URL url = new URL(questions.getImage());
            Glide.with(getContext()).load(url.toString()).into(image);
        } catch (MalformedURLException e) {
            e.printStackTrace();
        }

        return v;
    }
}

这部分没有执行。请帮忙。

Answer 1

我建议您在AsyncTask类中实现onPostExecute（）方法，并在其中创建和设置适配器，它可能是这样的：

    class GetOrders extends AsyncTask<Void, Void, List<ClientOrder>> {

                    @Override
                    protected List<ClientOrder> doInBackground(Void... voids) {
                        //here we get data from REST or database      
                        appDatabase.clientOrderDao().deleteById(id);
                        clientOrderList = appDatabase.clientOrderDao().getAll();
                        return clientOrderList;
                    }

                    @Override
                    protected void onPostExecute(List<ClientOrder> orders) {
                        super.onPostExecute(orders);
                        MyAdapter adapter = new Adapter(orders);
                        recyclerView.setAdapter(adapter);
                    }
                }

还有一个！从http服务获取数据的现代方法是Retrofit库，它非常有用，我建议您尝试一下：

https://square.github.io/retrofit/

Answer 2

嗨，请检查此更新的代码

public class MainActivity extends AppCompatActivity {
private static final String BASE_URL = "https://api.stackexchange.com/2.2/questions";
private EditText stackSearch;
private Button searchBtn;
private String text;
private StackAsyncTask stackAsyncTask;
private ArrayList<Questions> stackArrayList;
private String exception;
private ListView questionList;
private StackAdapter stackAdapter;

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

    stackArrayList = new ArrayList<>();


    stackAsyncTask = new StackAsyncTask();
    stackSearch = findViewById(R.id.book_genre);
    searchBtn = findViewById(R.id.btn_search);
    questionList = findViewById(R.id.book_list);
    //  progressBar = findViewById(R.id.progressBar);

    //add this both lines here
    stackAdapter = new StackAdapter(MainActivity.this, R.layout.questionlistitem, stackArrayList);
    questionList.setAdapter(stackAdapter);

    searchBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Log.i("kunal", "clicked");
            text = stackSearch.getText().toString();
            //        progressBar.setVisibility(View.VISIBLE);
            stackAsyncTask.execute();

        }
    });
}

class StackAsyncTask extends AsyncTask<Void, Void, Void> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected Void doInBackground(Void... voids) {
        Uri uri = Uri.parse(BASE_URL).buildUpon()
                .appendQueryParameter("order", "desc")
                .appendQueryParameter("sort", "activity")
                .appendQueryParameter("tagged", text)
                .appendQueryParameter("site", "stackoverflow")
                .build();
        URL url;
        try {
            url = new URL(uri.toString());
            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            httpURLConnection.connect();
            InputStream inputStream = httpURLConnection.getInputStream();
            InputStreamReader inputStreamReader = new InputStreamReader(inputStream, Charset.forName("UTF-8"));
            BufferedReader reader = new BufferedReader(inputStreamReader);
            StringBuilder buffer = new StringBuilder();
            String line = reader.readLine();
            while (line != null) {
                buffer.append(line);
                line = reader.readLine();
            }
            JSONObject questions = new JSONObject(buffer.toString());
            JSONArray items = questions.getJSONArray("items");
            for (int i = 0; i < 20; i++) {
                JSONObject first = items.getJSONObject(i);
                JSONObject owner = first.getJSONObject("owner");
                String profile_image = owner.getString("profile_image");
                String display_name = owner.getString("display_name");
                String view_count = first.getString("view_count");
                String answer_count = first.getString("answer_count");
                String score = first.getString("score");
                String last_activity_date = first.getString("last_activity_date");
                String creation_date = first.getString("creation_date");
                String link = first.getString("link");
                String title = first.getString("title");
                stackArrayList.add(new Questions(display_name, title, link, profile_image, view_count, answer_count, last_activity_date, creation_date, score));
            }
        } catch (Exception e) {
            exception = e.toString();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        stackAdapter.notifyDataSetChanged();
    }
} }

使用此代码继续编码：）