Question

我试着理解为什么我的变量result为空？我用Debug检查它，但我不明白为什么..我没有在我的设备中看到我的ImageView 这是我的代码：

public class ClassicView extends Activity {

private Content content;
public  LinearLayout view;
ClassicView classicView;
JSONParser jParser;
Context context;
private Bitmap bitmap;

private ImageView downloadedImg;
 private ProgressDialog simpleWaitDialog;
//RelativeLayout mainLayout;

RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams( new ViewGroup.MarginLayoutParams(
        RelativeLayout.LayoutParams.WRAP_CONTENT,
        RelativeLayout.LayoutParams.WRAP_CONTENT));

public ClassicView() {

}
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);


        JSONParser jParser = null;
        try {
            jParser = new JSONParser("Json.txt");
        } catch (IOException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }

        content = (Content)getIntent().getSerializableExtra("CONTENT");


            //this.setClassicLabel(jParser.getContentViewWithId(content.getElemView()).getJSONArray("Label"));
            //(jParser.getContentViewWithId(content.getElemView()).getJSONArray("Img"));

        try {
            this.setClassicImg();
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
    public void setClassicLabel(JSONArray listLabel) throws JSONException {
        RelativeLayout rl = new RelativeLayout(this);
        DisplayMetrics metrics = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(metrics);
        setContentView(rl);

        for (int i = 0; i < listLabel.length(); i++) {  
            TextView tv = new TextView(this);
            tv.setText(listLabel.getJSONObject(i).getString("text"));
            RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams((int) (metrics.widthPixels * listLabel.getJSONObject(i).getDouble("size_x")), (int) (metrics.heightPixels * listLabel.getJSONObject(i).getDouble("size_y")));
            params.leftMargin = (int) (metrics.widthPixels * listLabel.getJSONObject(i).getDouble("position_x"));
            params.topMargin = (int) (metrics.heightPixels * listLabel.getJSONObject(i).getDouble("position_y"));
            rl.addView(tv, params);

        }
    }

    public void setClassicImg() throws JSONException, IOException, MalformedURLException {
        RelativeLayout rl2 = new RelativeLayout(this);
        DisplayMetrics metrics = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(metrics);
        setContentView(rl2);
        ImageView downloadedImg = new ImageView(this);
        new DownloadImageTask(downloadedImg).execute("http://felicita-pizzeria.fr/images/logo.png");
        }





/* To Load Image */


    private class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {
        ImageView myimage;

        public DownloadImageTask(ImageView bmImage) {
            this.myimage = bmImage;
        }

        protected Bitmap doInBackground(String... urls) {
            String urldisplay = urls[0];
            Bitmap mIcon11 = null;
            try {
                InputStream in = new java.net.URL(urldisplay).openStream();
                mIcon11 = BitmapFactory.decodeStream(in);
            } catch (Exception e) {
                Log.e("Error", e.getMessage());
                e.printStackTrace();
            }
            return mIcon11;
        }

        protected void onPostExecute(Bitmap result) {
            myimage.setImageBitmap(result);
        }
    }`

有人可以帮我吗？谢谢

Answer 1

它是null，因为传递给任务构造函数的downloadedImg为null。您的代码没有显示您如何找到ImageView的代码，但很可能您要么找到该布局中不存在的imageView，要么您忘记完全执行此操作。

Answer 2

它提供nullpointer异常，因为您可能忘记初始化ImageView

中作为参数传递的new DownloadImageTask(downloadedImg).execute(..);

确保您已在班级中初始化了ImageView。

 ImageView downloadedImg =new ImageView(this);

使用以下代码从网址下载图片：

private Bitmap downloadBitmap(String url) {
     // initilize the default HTTP client object
     final DefaultHttpClient client = new DefaultHttpClient();

     //forming a HttoGet request 
     final HttpGet getRequest = new HttpGet(url);
     try {

         HttpResponse response = client.execute(getRequest);
             //check 200 OK for success
         final int statusCode = response.getStatusLine().getStatusCode();

         if (statusCode != HttpStatus.SC_OK) {
             Log.w("ImageDownloader", "Error " + statusCode + 
                     " while retrieving bitmap from " + url);
             return null;

         }

         final HttpEntity entity = response.getEntity();
         if (entity != null) {
             InputStream inputStream = null;
             try {
                 // getting contents from the stream 
                 inputStream = entity.getContent();

                 // decoding stream data back into image Bitmap that android understands
                 image = BitmapFactory.decodeStream(inputStream);


             } finally {
                 if (inputStream != null) {
                     inputStream.close();
                 }
                 entity.consumeContent();
             }
         }
     } catch (Exception e) {

         Log.e("ImageDownloader", "Something went wrong while" +
                 " retrieving bitmap from " + url + e.toString());
     } 

     return image;
 }

更改您的代码如下：

  private class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {
    ImageView myimage;

    public DownloadImageTask(ImageView bmImage) {
        this.myimage = bmImage;
    }

    protected Bitmap doInBackground(String... urls) {
        String urldisplay = urls[0];
        Bitmap mIcon11 = null;
        try {
                   mIcon11 = downloadBitmap(urldisplay);
        } catch (Exception e) {
            Log.e("Error", e.getMessage());
            e.printStackTrace();
        }
        return mIcon11;
    }

    protected void onPostExecute(Bitmap result) {
        myimage.setImageBitmap(result);
    }
}

<强>编辑：

这是我尝试过的代码，它的功能就像魅力一样。

public class MainActivity extends Activity {

    Bitmap image;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ImageView mm=new ImageView(getApplicationContext());

        new DownloadImageTask(mm).execute("http://felicita-pizzeria.fr/images/logo.png");
        setContentView(mm);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    private Bitmap downloadBitmap(String url) {
         // initilize the default HTTP client object
         final DefaultHttpClient client = new DefaultHttpClient();

         //forming a HttoGet request 
         final HttpGet getRequest = new HttpGet(url);
         try {

             HttpResponse response = client.execute(getRequest);
                 //check 200 OK for success
             final int statusCode = response.getStatusLine().getStatusCode();

             if (statusCode != HttpStatus.SC_OK) {
                 Log.w("ImageDownloader", "Error " + statusCode + 
                         " while retrieving bitmap from " + url);
                 return null;

             }

             final HttpEntity entity = response.getEntity();
             if (entity != null) {
                 InputStream inputStream = null;
                 try {
                     // getting contents from the stream 
                     inputStream = entity.getContent();

                     // decoding stream data back into image Bitmap that android understands
                     image = BitmapFactory.decodeStream(inputStream);


                 } finally {
                     if (inputStream != null) {
                         inputStream.close();
                     }
                     entity.consumeContent();
                 }
             }
         } catch (Exception e) {

             Log.e("ImageDownloader", "Something went wrong while" +
                     " retrieving bitmap from " + url + e.toString());
         } 

         return image;
     }

     private class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {
            ImageView myimage;

            public DownloadImageTask(ImageView bmImage) {
                this.myimage = bmImage;
            }

            protected Bitmap doInBackground(String... urls) {


        String urldisplay = urls[0];
            Bitmap mIcon11 = null;
            try {
                       mIcon11 = downloadBitmap(urldisplay);
            } catch (Exception e) {
                Log.e("Error", e.getMessage());
                e.printStackTrace();
            }
            return mIcon11;
        }

        protected void onPostExecute(Bitmap result) {
            myimage.setImageBitmap(result);
        }
    }

}

<强>输出：

enter image description here

为什么我在设备上看不到ImageView？

2 个答案: