Android: 执行 doInBackground , TextView 的 setText

Question

我是 android 和套接字编程的新手。我正在开发一个客户端向服务器发送字符串的项目。当服务器获取字符串时，将更改 TextView 的文本。问题是每当客户端发送字符串时，服务器就会崩溃(当我使用 setText() 函数时)。这是我的代码:

public class Download extends AppCompatActivity {


GetRequestedURLAsyncTask __getRequestedURLAsyncTask;

TextView incomingURL;
Button downloadButton;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_download);

    incomingURL = (TextView)  this.findViewById(R.id.incomingURL);
    downloadButton = (Button) this.findViewById(R.id.disconnectButton);


    __getRequestedURLAsyncTask = new GetRequestedURLAsyncTask(this);
    __getRequestedURLAsyncTask.execute(this);
}

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

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

private class GetRequestedURLAsyncTask extends AsyncTask {

    private Context context;
    private TextView statusText;

    private String requestedURL;

    public GetRequestedURLAsyncTask(Context context) {
        this.context = context;
    }

    @Override
    protected Object doInBackground(Object[] params) {

        ServerSocket serverSocket = null;
        Socket client = null;

        try {
            Log.v("transferService", "Creating server socket");
            serverSocket = new ServerSocket(8282);

            Log.v("transferService", "Creating client socket");
            client = serverSocket.accept();


            InetAddress inetAddress = client.getInetAddress();
            Log.d("New connection made from ", inetAddress.getHostAddress());

            Log.d("IncomingText", "Init input");

            DataInputStream input = new DataInputStream(client.getInputStream());



            while(true)
            {
                try
                {

                    requestedURL = input.readLine().toString();
                    Log.d("incomingText", requestedURL);
                    setRequestedUrl(requestedURL);
                }
                catch (IOException e)
                {

                }
            }





        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }

    }


    protected void onPostExecute(String result)
    {

        if (result != null)
        {
            setRequestedUrl(result);
        }
    }

    public String getRequestedUrl()
    {
        return this.requestedURL;
    }

}

private void setRequestedUrl(String s)
{
    this.incomingURL.setText(s);
}

和 logcat:

 FATAL EXCEPTION: AsyncTask #1
java.lang.RuntimeException: An error occured while executing doInBackground()
        at android.os.AsyncTask$3.done(AsyncTask.java:299)
        at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
        at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
        at java.util.concurrent.FutureTask.run(FutureTask.java:137)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
        at java.lang.Thread.run(Thread.java:856)
 Caused by: android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
        at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:4876)
        at android.view.ViewRootImpl.requestLayout(ViewRootImpl.java:948)
        at android.view.View.requestLayout(View.java:15245)
        at android.view.View.requestLayout(View.java:15245)
        at android.view.View.requestLayout(View.java:15245)
        at android.view.View.requestLayout(View.java:15245)
        at android.view.View.requestLayout(View.java:15245)
        at android.view.View.requestLayout(View.java:15245)
        at android.widget.RelativeLayout.requestLayout(RelativeLayout.java:292)
        at android.view.View.requestLayout(View.java:15245)
        at android.widget.TextView.checkForRelayout(TextView.java:6632)
        at android.widget.TextView.setText(TextView.java:3736)
        at android.widget.TextView.setText(TextView.java:3594)
        at android.widget.TextView.setText(TextView.java:3569)
        at Download.setRequestedUrl(Download.java:147)
        at Download.access$000(Download.java:24)
        at Download$GetRequestedURLAsyncTask.doInBackground(Download.java:109)
        at android.os.AsyncTask$2.call(AsyncTask.java:287)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)

任何建议都会有所帮助。

Answer 1

在 doInBackground 方法中删除对 setRequestedUrl(requestedURL) 的调用。 doInBackground 方法发生在主线程之外。您只能在 AsyncTask

的 onPreExecute、 onPostExecute 或 onProgressUpdate 方法中修改您的 View