我是
Android编程的新手,可以真正使用我正在编写的程序帮助建立Http连接并显示图像.
我正在使用Wei-Meng Lee的“Beginning Android Application Development”一书.代码编译并且没有标记错误,但每次运行程序时都会出现“错误连接”消息,并且不显示任何图像.
我查看了GET请求的各种代码示例,但找不到任何适用于我的代码的内容.
任何人都可以提供的任何帮助都将非常感激,因为到目前为止我正在努力寻找任何解决方案.
关于uses-permission的最后一行代码包含在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" />
最佳答案 也许问题是因为api版本.您必须使用AsyncTask类来访问Web功能.
这可能与以下事实有关:在apis 11及以上访问主线程中的网络是不允许的,您可能必须使用ASYNC任务.
使用ASYNC任务的示例;
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);
}
}
}