Question

我正在尝试从URL到ImageView获取图像我正在使用this类。我已经添加了连接到internet write_SD卡的权限等等，AndroidManifest问题是当我尝试使用此函数将图像添加到java.lang.NullPointerException时它返回错误ImageView：`< / p>

public void download(String url, ImageView imageView) {
    try
    {    
        if (cancelPotentialDownload(url, imageView)) 
        {
             //TODO:Caching code right here
             String filename = String.valueOf(url.hashCode());
             File f = new File(getCacheDirectory(hm), filename);

              // Is the bitmap in our cache?
              Bitmap bitmap = BitmapFactory.decodeFile(f.getPath());

              //No? download it
              if(bitmap == null){
                  BitmapDownloaderTask task = new BitmapDownloaderTask(imageView);
                  DownloadedDrawable downloadedDrawable = new DownloadedDrawable(task);
                  imageView.setImageDrawable(downloadedDrawable);
                  task.execute(url);
              }else{
                  //Yes? set the image
                  imageView.setImageBitmap(bitmap);
              }
         }
    }catch (Exception e) {
        // TODO: handle exception
        Log.e("",e.toString());
    }
}`

问题是什么可能是错的，我怎么能解决这个问题？如果你能指出我正确的方向，我将很高兴。

logcat的：

`06-06 09:38:19.686: E/AndroidRuntime(18832): java.lang.NullPointerException
06-06 09:38:19.686: E/AndroidRuntime(18832):    at com.jandans.geos.ImageDownloader.download(ImageDownloader.java:51)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at com.jandans.geos.vaikpied$1.onItemClick(vaikpied.java:98)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at android.widget.AdapterView.performItemClick(AdapterView.java:284)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at android.widget.ListView.performItemClick(ListView.java:3513)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at android.widget.AbsListView$PerformClick.run(AbsListView.java:1849)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at android.os.Handler.handleCallback(Handler.java:587)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at android.os.Handler.dispatchMessage(Handler.java:92)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at android.os.Looper.loop(Looper.java:130)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at android.app.ActivityThread.main(ActivityThread.java:3835)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at java.lang.reflect.Method.invokeNative(Native Method)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at java.lang.reflect.Method.invoke(Method.java:507)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:847)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
06-06 09:38:19.686: E/AndroidRuntime(18832):    at dalvik.system.NativeStart.main(Native Method)

`

Answer 1

以下代码段会对您有所帮助。

<强> DownloadHelper.java

public interface DownloadHelper
{
    public void OnSucess(Bitmap bitmap);
    public void OnFailure(String response);
}

<强> MainActivity.java

public class GalleryExample extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        setContentView(R.layout.main);

        DownloadHelper downloadHelper = new DownloadHelper()
        {
            @Override
            public void OnSucess(Bitmap bitmap)
            {
                ImageView imageView=(ImageView)findViewById(R.id.imageView);
                imageView.setImageBitmap(bitmap);
            }

            @Override
            public void OnFailure(String response)
            {
                Toast.makeText(context, response, Toast.LENGTH_LONG).show();
            }
        };
        new MyTask(this,downloadHelper).execute("image url");
    }

<强> MyTask.java

public class DownloadTask extends AsyncTask<String, Integer, Object>
{
    private Context context;
    private DownloadHelper downloadHelper;
    private ProgressDialog dialog;


    public DownloadTask(Context context,DownloadHelper downloadHelper)
    {
        this.context = context;

    }

    @Override
    protected void onPreExecute()
    {
        dialog = new ProgressDialog(context);
        dialog.setTitle("Please Wait");
        dialog.setMessage("Fetching Data!!");
        dialog.setCancelable(false);
        dialog.show();
        super.onPreExecute();
    }

    @Override
    protected Object doInBackground(String... params)
    {
        URL aURL = new URL(myRemoteImages[position]);
        URLConnection conn = aURL.openConnection();
        conn.connect();
        InputStream is = conn.getInputStream();

        BufferedInputStream bis = new BufferedInputStream(is);
        /* Decode url-data to a bitmap. */
        Bitmap bm = BitmapFactory.decodeStream(bis);
        bis.close();
        is.close();
        return bm;
    }

    @Override
    protected void onPostExecute(Object result)
    {
        dialog.dismiss();
        if (result != null)
        {
            downloadHelper.OnSucess((Bitmap)result);
        } 
        else
        {
            downloadHelper.OnFailure("Error in Downloading Data!!");
        }
        super.onPostExecute(result);
    }
}

Answer 2

尝试下面的一个 -

public class ImgLoadFrmWebActivity extends Activity {

    ImageView imv1;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Drawable image = ImageOperations(getApplicationContext(),"http://hvz.eu5.org/upload/1.jpg","image");
        ImageView imgView = (ImageView)findViewById(R.id.imageView1);
        imgView = (ImageView)findViewById(R.id.imageView1);
        imgView.setImageDrawable(image);
    }
    private Drawable ImageOperations(Context ctx, String url, String saveFilename) {
        try {
            InputStream is = (InputStream) this.fetch(url);
            Drawable d = Drawable.createFromStream(is, "src");
            return d;
        } catch (MalformedURLException e) {
            e.printStackTrace();
            return null;
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    public Object fetch(String address) throws MalformedURLException,IOException {
        URL url = new URL(address);
        Object content = url.getContent();
        return content;
    }
}

确保在清单文件中添加了权限 -

<uses-permission android:name="android.permission.INTERNET"></uses-permission>

只需根据您的需求自定义此布局。希望这会对你有所帮助。

E /（18707）：java.lang.NullPointerException

2 个答案: