Android：Http GET請求無法連接

Question

我是Android新手，我真的可以用一些幫助來編寫一個程序來建立一個Http連接並顯示一個圖像。

我正在使用Wei-Meng Lee的'Beginning Android Application Development'一書。代碼編譯並且沒有錯誤標記，但是每次運行程序時都會出現「錯誤連接」消息，並且不會顯示圖像。

我已經看過GET請求代碼的各種示例，但找不到任何適用於我的代碼的代碼。

任何人都可以提供的幫助將不勝感激，因爲我目前正在努力看到任何解決方案。

關於使用權限的最後一行代碼包含在Manifest中。

ImageView image; 

private InputStream OpenHttpConnection(String urlString) 
throws IOException { 
    InputStream in = null; 
    int response = -1; 

    URL url = new URL(urlString); 
    URLConnection conn = url.openConnection(); 

    if(!(conn instanceof HttpURLConnection)) 
     throw new IOException("Not an HTTP Connection"); 

    try { 
     HttpURLConnection httpConn = (HttpURLConnection) conn; 
     httpConn.setAllowUserInteraction(false); 
     httpConn.setInstanceFollowRedirects(true); 
     httpConn.setRequestMethod("GET"); 
     httpConn.connect(); 
     response = httpConn.getResponseCode(); 
     if (response == HttpURLConnection.HTTP_OK) { 
      in = httpConn.getInputStream(); 
     } 
    } 
    catch (Exception ex) { 
     throw new IOException("Error connecting"); 
    } 
    return in; 

} 

private Bitmap DownloadImage(String URL) { 
    Bitmap bitmap = null; 
    InputStream in = null; 
    try { 
     in = OpenHttpConnection(URL); 
     bitmap = BitmapFactory.decodeStream(in); 
     in.close(); 
    } 
    catch (IOException e1) { 
     Toast.makeText(this, e1.getLocalizedMessage(), Toast.LENGTH_LONG).show(); 
     e1.printStackTrace(); 
    } 
    return bitmap; 
}                                          

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

    Bitmap bitmap = DownloadImage("http://www.mayoff.com/5-01cablecarDCP01934.jpg"); 
    image = (ImageView) findViewById(R.id.image); 
    image.setImageBitmap(bitmap); 

} 

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

Answer 1

也許問題是你有因爲api版本。您必須使用AsyncTask類來訪問Web功能。

這可能與apis 11及以上版本在主線程中不允許訪問網絡有關，因此您可能必須使用ASYNC任務。

使用ASYNC任務的示例;

class InternetFileCheack extends AsyncTask<Object, Void, Boolean> { 

    private Button btn; 
    private String fileURL; 
    Context c; 

    public InternetFileCheack (Button imv, String url, Context ctx) { 
    this.btn = imv; 
    this.fileURL = url; 
    this.c = ctx; 
    } 

    @Override 
    protected Boolean doInBackground(Object... params) { 
    Boolean sonuc = null; 
    try { 
    URL u = new URL(fileURL); 
    HttpURLConnection huc = (HttpURLConnection) u.openConnection(); 
    huc.setRequestMethod("HEAD"); 
    huc.connect(); 
    int code = huc.getResponseCode(); 

    if (code == HttpURLConnection.HTTP_OK) { 
    sonuc = true; 
    } else { 
    sonuc = false; 
    } 
    } catch (Exception e) { 
    sonuc = false; 
    } 
    return sonuc; 
    } 

    @Override 
    protected void onPostExecute(Boolean result) { 
    btn.setEnabled(result); 

    if (result) { 
    Toast.makeText(c, "", Toast.LENGTH_LONG).show(); 
    btn.setVisibility(View.VISIBLE); 
    } else { 
    btn.setVisibility(View.GONE); 
    } 
    } 
}