android-Android 開發中，訪問網絡的問題

Android 開發中，訪問網絡的問題

 public class MainActivity extends Activity {
    private EditText address;
    private Button getbutton;
    private TextView text;




    @Override
    protected void onCreate(Bundle savedInstanceState) {
        //版本4.0後需加這個，不然就報錯android.os.NetworkOnMainThreadException
        StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
                .detectDiskReads().detectDiskWrites().detectNetwork()
                .penaltyLog().build());
        StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder()
                .detectLeakedSqlLiteObjects().detectLeakedClosableObjects()
                .penaltyLog().penaltyDeath().build());
        //
        super.onCreate(savedInstanceState);
        setContentView(R.layout.test);
        //初始化

        address = (EditText) findViewById(R.id.address);
        getbutton = (Button) findViewById(R.id.getbutton);
        text = (TextView) findViewById(R.id.text);



        getbutton.setOnClickListener(new Button.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                String url = address.getText().toString();
                getPDAServerData(url);
            }
        });

    }

    public void getPDAServerData(String url) {
        HttpClient client = new DefaultHttpClient();
        HttpPost request;

        try {

            request = new HttpPost(url);

            //調用HttpClient對象的execute(HttpUriRequest request)發送請求，返回一個HttpResponse
            HttpResponse response = client.execute(request);

            //返回響應碼為200
            if (response.getStatusLine().getStatusCode() == 200) {

                //從響應中獲取消息實體
                HttpEntity entity = response.getEntity();
                if (entity != null) {
                    String out = EntityUtils.toString(entity);
                    text.setText(out);
                }
            }


        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

}

請問，

 StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
                .detectDiskReads().detectDiskWrites().detectNetwork()
                .penaltyLog().build());
        StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder()
                .detectLeakedSqlLiteObjects().detectLeakedClosableObjects()
                .penaltyLog().penaltyDeath().build());

這段代碼的意思是什麼呢，為什麼不加，就無法執行訪問網絡的代碼語句呢。

最佳回答：

request = new HttpPost(url);
//調用HttpClient對象的execute(HttpUriRequest request)發送請求，返回一個HttpResponse
HttpResponse response = client.execute(request);

這部分是網絡操作，必須在子線程執行，沒有這段代碼就會拋出android.os.NetworkOnMainThreadException；
而這個StrictMode主要是用來調試程序的，這段代碼可以檢測到android.os.NetworkOnMainThreadException
異常並發出警告 penaltyLog()表示將警告輸出到LogCat。
StrictMode 用法：http://www.2cto.com/kf/201503/381354.html