Android：如何在下载完成后恢复主线程

Question

如果我在任何Activity中并且我想下载一个文件（使用线程）并且同时我希望主线程等待下载完成，我该怎么办？ ？

Answer 1

使用AsyncTask ..从活动

new DownloadTask(this).execute(); 

任务，例如：

public class DownloadTask extends AsyncTask<Void, Void, String> { 

private ProgressDialog progressDialog; 
private Context context; 

/** 
* 
* @param context 
* @param pdfDoc the document of the PDF 
*/ 
public DownloadTask(Context context) { 
    this.context = context; 

    progressDialog = new ProgressDialog(context); 
} 

@Override 
protected void onPreExecute() { 
     progressDialog.setMessage("Downloading..."); 
     progressDialog.setIndeterminate(true); 
     progressDialog.show(); 
} 

@Override 
protected String doInBackground(Void... arg0) { 
    //download here 
} 

@Override 
protected void onPostExecute(final String result) { 
     progressDialog.dismiss(); 

} 
} 

Answer 2

使用的AsyncTask和回调。如果你想线程与他主线程沟通，告诉下载完成后，使用handler 这个代码将有助于

downloadString("http://www.route.to.your.string.com", new DownloadCallback<String>(){ 
    public void onFinishDownloading(String downloadedResult){ 
     Toast.makeText(YourActivityName.this, downloadedResult, Toast.LENGTH_SHORT).show(); 
    } 
}); 

Answer 3

：

public interface DownloadCallback<T>{ 
    public void onFinishDownload(T downloadedResult); 
} 


public static void downloadString(String url, DownloadCallback<String> callback){ 
    new AsyncTask<Void,Void,Void>(){ 

     String result;    

     @Override 
     protected void onPreExecute() { 
      // Do things before downloading on UI Thread 
     } 

     @Override 
     protected String doInBackground(Void... arg0) { 

      //download here 
      result = download(url); 

     } 

     @Override 
     protected void onPostExecute(final Void result) { 
      // Do things on UI thread after downloading, then execute your callback 
      if (callback != null) callback.onFinishDownloading(result); 
     } 


    }.execute(); 
} 

，并利用这一点，你只是这样做你了解它

MyHnadler handler; 
onCreate(Bundle savedInstance) 
{ 
setContent.. 
... 
handler=new MyHandler(); 
new MyThread().start(); 
} 
public class MyHandler extends Handler 
{ 
    @Override 
    public void handleMessage(Message message) { 
      switch (message.what) { 
      case 1: //....threading over 
         //write your code here 
        break; 
      case2 : //if you want to be notiifed of something else 
        .. 
} 

public class MyThread extends Thread 
{ 
@Override 
public void run() 
{ 
    //run the threa 
    //and when over 
    Message msg=handler.getMessage(); 
    msg.what=1; 
    handler.sendMessage(msg); //send the message to handler 
} 
} 
} 

正如你可以看到线程交通技术通过处理程序通过UI线程处理。在上面的例子中，我只将任何对象从线程发送到UI线程。要做到这一点，只需在线程中执行msg.obj=your_obj。它可以是任何对象。希望这可以帮助你:)