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[英]Why can't I see the layout preview in Android Studio but instead I see a 'cross' sign and am not able to add any elements?
[英]why i am not able to download any html page of any website?(i am using android studio)
public class MainActivity extends AppCompatActivity{
对于下载 html 页面,这甚至没有返回失败
public class DownloadTask extends AsyncTask<String,Void,String>{
@Override
protected String doInBackground(String... urls){
String result = "";
URL url;
HttpURLConnection urlConnection = null;
try{
url = new URL(urls[0]);
urlConnection = (HttpURLConnection) url.openConnection();
InputStream in = urlConnection.getInputStream();
InputStreamReader reader = new InputStreamReader(in);
int data = reader.read();
while(data!=-1){
char current = (char) data;
result+=current;
}
return result;
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return "failed";
}
}
当我在OnCreate 中执行它时,我在Logcat 中什么也没得到(在这里我打印了我存储 html 页面的变量。)
正如在您的课程中所见,您没有传递任何参数(网址)进行处理。
你需要在你的类中创建一个参数化的构造函数来传递数据。 像下面,
public class DownloadTask extends AsyncTask<String,Void,String>{
private String url1;
public DownloadTask(String url1){
this.url1=url1;
}
//rest of your code
try{
url = new URL(url1);
}catch(Exception e){}
//rest of your code
}
希望这可以帮助。
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