Java 将图像从 URL 加载到 Listview

Question

现在 3 天后，我认为最好在接下来的 3 天没有结果之前问清楚。

现状：我通过 PHP API 作为 JSON 获取数据。 数据已解析，我现在将图像的 URL 作为“字符串？”。 实际上 URL 在 Listview 中显示为文本 URL。

现在的问题是如何在 listView 中显示来自 URL 的图像？

使用以下代码，URL 在 listView 中显示为文本 - 这是有效的。

 ListAdapter adapter = new SimpleAdapter(this, mProductMapList, R.layout.list_product_categories,
                new String[] { KEY_ID, KEY_NAME, KEY_IMAGE},
               new int[] { R.id.id,R.id.name, R.id.image});
                new String[]{KEY_VER,KEY_NAME},new int[]{R.id.id,R.id.title});
       mListView.setAdapter(adapter);

所以我认为问题是 SimpleAdapter。 我还创建了一个这样的自定义适配器：

    ListView list= (ListView) this.findViewById(R.id.list_view);
    ListAdapter adapter =
            new MyAdapter(
                    this,
                    mProductMapList,
                    R.layout.list_product_categories,
                    new String[]{KEY_ID,KEY_NAME,KEY_IMAGE},
                    new int[]{R.id.id,R.id.name,R.id.image});
    list.setAdapter(adapter);

MyAdapter.java：

    package com.learn2crack.listviewjson;

import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.SimpleAdapter;

import com.squareup.picasso.Picasso;

import java.util.List;
import java.util.Map;

/**
 * Created by Michael on 07.11.2017.
 */

public class MyAdapter extends SimpleAdapter {
  //String KEY_IMAGE = "image";
        public MyAdapter(Context context, List<? extends Map<String, ?>> data, int resource, String[] from, int[] to){
            super(context, data, resource, from, to);
        }

        public View getView(int position, View convertView, ViewGroup parent){
            // here you let SimpleAdapter built the view normally.
            View v = super.getView(position, convertView, parent);

            // Then we get reference for Picasso
            ImageView img = (ImageView) v.getTag();
            if(img == null){
                img = (ImageView) v.findViewById(R.id.image);
                v.setTag(img); // <<< THIS LINE !!!!
            }
            // get the url from the data you passed to the `Map`
           // String url = ((Map)getItem(position)).get();
            // do Picasso
            Picasso.with(v.getContext()).load("http://copy-cat.at/wp-content/uploads/2014/06/as11.jpg").into(img);

            // return the view
            return v;
        }

}

完整 Shop.java（主）

    package com.learn2crack.listviewjson;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Spinner;
import android.widget.Toast;

import com.learn2crack.listviewjson.model.AndroidVersion;
import com.learn2crack.listviewjson.model.ProductDetails;
import org.json.JSONObject;
import com.learn2crack.listviewjson.model.ResponseProduct;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Scanner;

import com.learn2crack.listviewjson.ImageAdapter;
import com.squareup.picasso.Picasso;
import com.squareup.picasso.Target;

public class Shop extends AppCompatActivity implements LoadJSONTaskShop.listenerShop, AdapterView.OnItemClickListener {


    private ListView mListView;
    private Context context;
    ImageView imagee;
    public static final String URL = "http://copy-cat.at/api/?act=getProductCategories";
//http://copy-cat.at/api/?act=getProductCategories
    private List<HashMap<String, String>> mProductMapList = new ArrayList<>();

    private static final String KEY_ID = "id";
    private static final String KEY_NAME = "title";
    private static final String KEY_IMAGE = "image";



    private Spinner spinner1, spinner2;
    private Button btnSubmit;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_shop);
        Log.e("TESTLOGSHOP", "SHOP");

        //instantiate your listView
       // ListView nameAndAgeListView = (ListView) findViewById(R.id.gridview);

//create your listView with your custom object
      //  ArrayList<ImageAdapter> nameAndAgeList = new ArrayList<>();

        mListView = (ListView) findViewById(R.id.list_view);
        ImageView imagee= (ImageView) findViewById(R.id.image); // your imageview onbject

       // context = this;
       // String imageUri = "https://i.imgur.com/tGbaZCY.jpg";
      //  ImageView ivBasicImage = (ImageView) findViewById(R.id.imagee);
        //Picasso.with(getApplicationContext()).load(imageUri).into(ivBasicImage);



        // ImageView imageView = (ImageView) findViewById(R.id.image);
        // Glide.with(this).load("http://i.imgur.com/DvpvklR.png").into(imageView);

      // mListView.setOnItemClickListener(this);
       // mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
          // @Override
           // public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,long arg3) {
               // Intent i= new Intent(Shop.this,ShowProductDetails.class);
               //Sring itemString= mProductMapList.get(arg2).get(KEY_VER);
               // i.putExtra("productid",itemString);
               // Log.e("TESTLOG", itemString);

               // startActivity(i);
               // finish();
         //   }
     //   });
        new LoadJSONTaskShop(this).execute(URL);


        getCategories();

        addItemsOnSpinner2();
        addListenerOnButton();
        addListenerOnSpinnerItemSelection();

        String URL ="";
    // new LoadJSONTaskShop(this).execute(URL);

    }

    public void getCategories() {
        String URL ="";
        mListView = (ListView) findViewById(R.id.list_view);
       // new LoadJSONTaskShop(this).execute(URL);
    }



    // add items into spinner dynamically
    public void addItemsOnSpinner2() {

        spinner2 = (Spinner) findViewById(R.id.spinner2);

        String URL ="";
        //new LoadJSONTaskShop(this).execute(URL);



        List<String> list = new ArrayList<String>();
        list.add("list 1");
        list.add("list 2");
        list.add("list 3");
        ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_spinner_item, list);
        dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner2.setAdapter(dataAdapter);
    }

    public void addListenerOnSpinnerItemSelection() {
        spinner1 = (Spinner) findViewById(R.id.spinner1);
        spinner1.setOnItemSelectedListener(new CustomOnItemSelectedListener());
    }

    // get the selected dropdown list value
    public void addListenerOnButton() {

        spinner1 = (Spinner) findViewById(R.id.spinner1);
        spinner2 = (Spinner) findViewById(R.id.spinner2);
        btnSubmit = (Button) findViewById(R.id.btnSubmit);

        btnSubmit.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {

                Toast.makeText(Shop.this,
                        "OnClickListener : " +
                                "\nSpinner 1 : "+ String.valueOf(spinner1.getSelectedItem()) +
                                "\nSpinner 2 : "+ String.valueOf(spinner2.getSelectedItem()),
                        Toast.LENGTH_SHORT).show();
            }

        });
    }

    public void onClick(View v) {
        startActivity(new Intent(this, Shop.class));
        finish();

    }
    ///////////
  //  @Override
    public void onLoaded(List<ProductDetails> productDetails) {

        for (ProductDetails android : productDetails) {

         //   HashMap<String, String> map = new HashMap<>();
            HashMap<String, String> map = new HashMap<String, String>();

            map.put(KEY_ID, android.getId());
            map.put(KEY_NAME, android.getName());
            map.put(KEY_IMAGE, android.getImage());


           // new DownloadImage((ImageView) findViewById(R.id.image))
                  //  .execute("http://copy-cat.at/wp-content/uploads/2014/06/as11.jpg");

            String URL = "http://copy-cat.at/wp-content/uploads/2014/06/as11.jpg";
         //  new DownloadImage((ImageView) findViewById(R.id.imagee)).execute(URL);
          new DownloadImage();
           // Picasso.with(this).load("http://copy-cat.at/wp-content/uploads/2014/06/as11.jpg").into(imagee);
            Log.e("TESTLOGSHOPxx", android.getImage());

            mProductMapList.add(map);

        }

        loadListView();
    }

    @Override
    public void onError() {

        Toast.makeText(this, "Error !", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {

       // Toast.makeText(this, mProductMapList.get(i).get(KEY_NAME),Toast.LENGTH_LONG).show();
        //ShowProduct.getProduct(this);
        Toast.makeText(this, "Error !", Toast.LENGTH_SHORT).show();
    }

    private void loadListView() {

        //ListAdapter adapter = new SimpleAdapter(this, mProductMapList, R.layout.list_product_categories,
               // new String[] { KEY_ID, KEY_NAME, KEY_IMAGE},
               // new int[] { R.id.id,R.id.name, R.id.image});
                //new String[]{KEY_VER,KEY_NAME},new int[]{R.id.id,R.id.title});
      // mListView.setAdapter(adapter);

        ListView list= (ListView) this.findViewById(R.id.list_view);
        ListAdapter adapter =
                new MyAdapter(
                        this,
                        mProductMapList,
                        R.layout.list_product_categories,
                        new String[]{KEY_ID,KEY_NAME,KEY_IMAGE},
                        new int[]{R.id.id,R.id.name,R.id.image});
        list.setAdapter(adapter);

    }


    // NAVIGATION
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.main_menu, menu);
        return true;
    }




}

错误：

java.lang.IllegalArgumentException: Target must not be null.
                                                                            at com.squareup.picasso.RequestCreator.into(RequestCreator.java:607)
                                                                            at com.squareup.picasso.RequestCreator.into(RequestCreator.java:590)
                                                                            at com.learn2crack.listviewjson.MyAdapter.getView(MyAdapter.java:37)

这里是 list_product_categories.xml

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


<ImageView
    android:id="@+id/flag"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:contentDescription="@string/search"
    android:paddingTop="10dp"
    android:paddingRight="10dp"
    android:paddingBottom="10dp"
    />


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


    <TextView
        android:id="@+id/name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="5dp"
        android:textSize="20dp"
        android:textColor="#88000000"
        android:layout_weight="1"
        />

<ImageView
    android:id="@+id/imagee"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="5dp"
    android:textSize="20dp"
    android:textColor="#88000000"
    android:layout_weight="1"
    />

问题是什么？ 您可以在代码中看到我测试了更多以设置显示图像但我是新手并且它并不那么容易...... 我希望你可以帮助我 ：） 非常感谢！

干杯，迈克尔

编辑： 现在我已经修复了很多很多，非常感谢你们！

解决方案：

 // Then we get reference for Picasso
            ImageView img = (ImageView) v.findViewById(R.id.imagee);
            Log.e("", img.toString());
            if(img == null){
                img = (ImageView) v.findViewById(R.id.imagee);
                v.setTag(img); // <<< THIS LINE !!!!
            }

现在它工作正常:)

Answer 1

您的img 变量为空（代码img = (ImageView) v.findViewById(R.id.image); 显然不能正常工作），因此它在抱怨。