如何在 Android 中使用 Asynctask 类更改 UI 数据？

Question

我想知道使用 Asynctask 类 (LocationAsyncTask.java) 和 Activity 更改 UI 数据 (ListView) 的最佳方式是什么。

我有这个异常错误：

Error:(40, 5) error: method does not override or implement a method from a supertype

已编辑：

我有这个 Asynctask 类（LocationAsyncTask.java）：

public abstract class LocationAsyncTask extends AsyncTask{

    public ArrayList<Location> locationList;

    public Context context;

    public LocationAsyncTask(Context context) {
        this.context = context;
    }

    @Override
    protected Object doInBackground(Object[] objects) {
        try {
            //These lines are an example(I will obtain the data via internet)
            Location ejemplo = new Location("Locality1","name","address");
            Location ejemplo2 = new Location("Locality2","name2","address2");
            locationList = new ArrayList<Location>();
            locationList.add(ejemplo);
            locationList.add(ejemplo2);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {}

}

这是我的 Activity 类：

public class LocationNativeActivity extends Activity {
    ArrayList<Location> locationList;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        LocationAsyncTask myTask = new LocationAsyncTask(this){
            @Override
            protected void onPostExecute(Void aVoid) {
                ListView s = (ListView)(findViewById(R.id.lvlocationnative));
                ArrayAdapter<Location> adapter = new ArrayAdapter<Location>(context, android.R.layout.simple_list_item_1, locationList);
                s.setAdapter(adapter);
            }
        };

        myTask.execute();

    }

}

这是我的布局：

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

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

</LinearLayout>

这是我的位置类：

public class Location {

    private String addressLocality;
    private String name;
    private String address;

    public Location(String addressLocality,String name, String address) {
        this.addressLocality = addressLocality;
        this.name = name;
        this.address = address;
    }

    public String getAddressLocality() {
        return addressLocality;
    }

    public void setAddressLocality(String addressLocality) {
        this.addressLocality = addressLocality;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return this.addressLocality; 
    }

}

使用此代码我无法在 Listview 中插入数据，有什么建议吗？

我检查了这些帖子：

• https://stackoverflow.com/a/15409989/3739382
• https://stackoverflow.com/a/35193172/3739382

Answer 1

您的方法存在很多问题，@Jyoti 刚刚强调了其中一个问题。您不能像使用复杂对象一样简单地使用 ArrayAdapter。它不会产生有用的结果。相反，您需要创建 CustomAdapter。

1. 创建自定义项目视图让我们说 item_location.xml 在布局文件夹下并输入以下代码：

   <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
       android:layout_width="match_parent"
       android:orientation="vertical"
       android:layout_height="match_parent" >
       <TextView
           android:id="@+id/tvaddressLocality"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:textStyle="bold"
           android:text="Address Locality" />
       <TextView
           android:id="@+id/tvName"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
          android:text="Name" />
   
       <TextView
           android:id="@+id/tvAddress"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:text="Address" /></LinearLayout>
   

2. 如下创建CustomAdapter类：

   import android.content.Context;    
   import android.support.annotation.NonNull;    
   import android.view.LayoutInflater;    
   import android.view.View;    
   import android.view.ViewGroup;    
   import android.widget.ArrayAdapter;    
   import android.widget.TextView;            
   import java.util.ArrayList;
   
   public class CustomLocationAdapter  extends ArrayAdapter<Location> {
   
       public CustomLocationAdapter(@NonNull Context context, ArrayList<Location> locations) {
           super(context,0, locations);
       }
   
       @Override
       public View getView(int position, View convertView, ViewGroup parent) {
           // Get the data item for this position
           Location location = getItem(position);
           // Check if an existing view is being reused, otherwise inflate the view
           if (convertView == null) {
               convertView = LayoutInflater.from(getContext()).inflate(R.layout.item_location, parent, false);
           }
           // Lookup view for data population
           TextView tvAddressLocality = (TextView) convertView.findViewById(R.id.tvaddressLocality);
           TextView tvName = (TextView) convertView.findViewById(R.id.tvName);
           TextView tvAddress = (TextView) convertView.findViewById(R.id.tvAddress);
           // Populate the data into the template view using the data object
           tvAddressLocality.setText(location.getAddressLocality());
           tvName.setText(location.getName());
           tvAddress.setText(location.getAddress());
           // Return the completed view to render on screen
           return convertView;
       }
   }
   

3. 如下更新您的LocationAsyncTask：

    public class LocationAsyncTask extends AsyncTask {
   
       private ArrayList<Location> locationList;
       private final WeakReference<ListView> listViewWeakReference;
   
       private Context context;
   
       public LocationAsyncTask(ListView listView, Context context) {
           this.listViewWeakReference = new WeakReference<>(listView);
           this.context = context;
       }
   
       @Override
       protected Object doInBackground(Object[] objects) {
           try {
               //These lines are an example(I will obtain the data via internet)
               Location ejemplo = new Location("Locality1s", "name", "address");
               Location ejemplo2 = new Location("Locality2", "name2", "address2");
               locationList = new ArrayList<Location>();
               locationList.add(ejemplo);
               locationList.add(ejemplo2);
           } catch (Exception e) {
               e.printStackTrace();
           }
           return null;
       }
   
       @Override
       protected void onPostExecute(Object o) {
           super.onPostExecute(o);
           ArrayAdapter<Location> adapter = new CustomLocationAdapter(context, locationList);
           listViewWeakReference.get().setAdapter(adapter);
       }
   }
   

4. 更新你LocationNativeActivity.onCreate()如下：

   ListView listView = LocationNativeActivity.this.findViewById(R.id.lvlocationnative);

   LocationAsyncTask myTask = new LocationAsyncTask(listView, this);

   myTask.execute();

Answer 2

你可以替换你的代码：

LocationAsyncTask myTask = new LocationAsyncTask(this);

作为：

LocationAsyncTask myTask = new LocationAsyncTask(this){
            @Override
            protected void onPostExecute(Void aVoid) {
                  ListView s = (ListView)(findViewById(R.id.lvlocationnative));
                  ArrayAdapter<Location> adapter = new ArrayAdapter<Location>(context, android.R.layout.simple_list_item_1, locationList);
                  s.setAdapter(adapter);  
            }
};

在您的异步任务中：

• 将 arrayList 设为公开

• 使用这个onPostExecute() 方法：

  protected void onPostExecute(Void aVoid) {}