Question

我正在尝试使用通用图像加载器在网格视图中获取图像。但是，一旦我创建了这段代码，日志开始就会出现一些错误

04-03 21:45:12.653: E/AndroidRuntime(1271): FATAL EXCEPTION: main
04-03 21:45:12.653: E/AndroidRuntime(1271): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.nostra13.example.universalimageloader/com.nostra13.example.universalimageloader.ImageGridActivity}: java.lang.NullPointerException
04-03 21:45:12.653: E/AndroidRuntime(1271):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at android.os.Looper.loop(Looper.java:123)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at android.app.ActivityThread.main(ActivityThread.java:3683)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at java.lang.reflect.Method.invokeNative(Native Method)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at java.lang.reflect.Method.invoke(Method.java:507)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at dalvik.system.NativeStart.main(Native Method)
04-03 21:45:12.653: E/AndroidRuntime(1271): Caused by: java.lang.NullPointerException
04-03 21:45:12.653: E/AndroidRuntime(1271):     at com.nostra13.example.universalimageloader.ImageGridActivity$ImageAdapter.getCount(ImageGridActivity.java:78)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at android.widget.GridView.setAdapter(GridView.java:131)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at com.nostra13.example.universalimageloader.ImageGridActivity.onCreate(ImageGridActivity.java:59)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-03 21:45:12.653: E/AndroidRuntime(1271):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)

这里的代码是这样的 Constants.java

import java.util.ArrayList;
import java.util.HashMap;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.util.Log;

//import com.example.parseimage.JSONParser;

public final class Constants {

    public static String url = "http://ensign119.com/assets/image11.php";

    public static String[] IMAGES;

    protected static final String TAG_PRODUCTS = "image_path";
    protected static final String TAG_CID = "file_id";
    public static final String TAG_NAME = "file_name";

    ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();
    JSONParser jParser = new JSONParser();
    JSONArray products = null;

    private Constants() {
        JSONObject json = jParser.getJSONFromUrl(url);

        Log.d("path_parsing", "before parsing");
        try {
            // Getting Array of Contacts
            products = json.getJSONArray(TAG_PRODUCTS);

            // looping through All Contacts
            for(int i = products.length()-1; i >=0; i--){
                JSONObject c = products.getJSONObject(i);

                // Storing each json item in variable
                String cid = c.getString(TAG_CID).toString();
                String name = c.getString(TAG_NAME);
                // creating new HashMap
                HashMap<String, String> map = new HashMap<String, String>();

                // adding each child node to HashMap key => value
                map.put(TAG_CID, cid);
                map.put(TAG_NAME, name);

                // adding HashList to ArrayList
                mylist.add(map);
                Log.d("mylist_value", mylist.toString());
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
        Log.d("path_parsing", "after parsing");   

        IMAGES = new String[mylist.size()];
        for(int i=0; i<mylist.size(); i++){
           IMAGES[i] = mylist.get(i).get("file_name");
        }
        for(String path: IMAGES){
            Log.d("path", path.toString());
        }
    }

    public static class Config {
        public static final boolean DEVELOPER_MODE = false;
    }

    public static class Extra {
        public static final String IMAGES = "com.nostra13.example.universalimageloader.IMAGES";
        public static final String IMAGE_POSITION = "com.nostra13.example.universalimageloader.IMAGE_POSITION";
    }


}

imageGridActivity.java

import android.content.Intent;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;

import com.nostra13.example.universalimageloader.Constants.Extra;
import com.nostra13.universalimageloader.core.DisplayImageOptions;

public class ImageGridActivity extends AbsListViewBaseActivity {

    String[] imageUrls;

    DisplayImageOptions options;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.ac_image_grid);

        Bundle bundle = getIntent().getExtras();
        imageUrls = bundle.getStringArray(Extra.IMAGES);

        options = new DisplayImageOptions.Builder()
            .showStubImage(R.drawable.ic_stub)
            .showImageForEmptyUri(R.drawable.ic_empty)
            .showImageOnFail(R.drawable.ic_error)
            .cacheInMemory()
            .cacheOnDisc()
            .bitmapConfig(Bitmap.Config.RGB_565)
            .build();

        listView = (GridView) findViewById(R.id.gridview);
        ((GridView) listView).setAdapter(new ImageAdapter());
        listView.setOnItemClickListener(new OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                startImagePagerActivity(position);
            }
        });
    }

    private void startImagePagerActivity(int position) {
        Intent intent = new Intent(this, ImagePagerActivity.class);
        intent.putExtra(Extra.IMAGES, imageUrls);
        intent.putExtra(Extra.IMAGE_POSITION, position);
        startActivity(intent);
    }

    public class ImageAdapter extends BaseAdapter {
        @Override
        public int getCount() {
            return imageUrls.length;
        }

        @Override
        public Object getItem(int position) {
            return null;
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            final ImageView imageView;
            if (convertView == null) {
                imageView = (ImageView) getLayoutInflater().inflate(R.layout.item_grid_image, parent, false);
            } else {
                imageView = (ImageView) convertView;
            }

            imageLoader.displayImage(imageUrls[position], imageView, options);

            return imageView;
        }
    }
}

请帮我解决这个问题。我是android的新手。

Answer 1

我猜你的问题来自这一行：

imageLoader.displayImage(imageUrls[position], imageView, options);

确认imageView，imageUrls at position（位置）和options对象不是NULL。

Answer 2

stacktrace中的这一行：

04-03 21:45:12.653: E/AndroidRuntime(1271): Caused by: java.lang.NullPointerException
04-03 21:45:12.653: E/AndroidRuntime(1271):     at com.nostra13.example.universalimageloader.ImageGridActivity$ImageAdapter.getCount(ImageGridActivity.java:78)

建议您的getCount方法返回null，这表示imageUrls为空，因为imageUrls.length也将为空，为您提供NullPointerException

另一个问题是你在这里做了什么：

@Override
public Object getItem(int position) {
    return null;
}

当Android尝试检索您的视图时，您将其赋予null，这在某些时候也会导致NullPointerException。如果您不确定自己在做什么，请不要覆盖方法。如果您强制覆盖方法，请确保您确切知道操作系统需要什么。仅仅因为您没有在自己的代码中使用getItem()，并不意味着Android不会使用它。

Answer 3

假设您的imageUrls[]数组不为空或为空，我认为您的问题位于getItem( int position )。尝试更改如下。

 public class ImageAdapter extends BaseAdapter {
        @Override
        public int getCount() {
            return imageUrls.length;
        }

        @Override
        public Object getItem(int position) {
            return imageUrls.get(i); // change here like this
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            final ImageView imageView;
            if (convertView == null) {
                imageView = (ImageView) getLayoutInflater().inflate(R.layout.item_grid_image, parent, false);
            } else {
                imageView = (ImageView) convertView;
            }

            imageLoader.displayImage(imageUrls[position], imageView, options);

            return imageView;
        }
    }
}

android.app.activitythread上的NullPointerException

3 个答案: