Android 4主线程访问网络

妖狐艹你老母 2024-02-17 15:42 50阅读 0赞

Android项目访问webservice，同样的程序在Android2.3上运行完全正常，而跑到Android4上面，bug出现了...

看了一下异常：android.os.NetworkOnMainThreadException

然后，上网搜索一下才发现，原来Android4默认情况下是不允许在主线程中访问网络的。

解决问题的思路有两种：

1、解除主线程网络访问限制，参见[http://developer.android.com/reference/android/os/StrictMode.html][http_developer.android.com_reference_android_os_StrictMode.html]

在onCreate中加入以下代码即可：

StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
                     .detectDiskReads()
                     .detectDiskWrites()
                     .detectNetwork()   // or .detectAll() for all detectable problems
                     .penaltyLog()
                     .build());
             StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder()
                     .detectLeakedSqlLiteObjects()
                     .detectLeakedClosableObjects()
                     .penaltyLog()
                     .penaltyDeath()
                     .build());

不过如果要求至少是API-9才可以，否则会编译器提示错误，所以在适配一些低版本系统时候不太给力。

2、多线程中访问网络-既然系统默认不允许在主线程中访问，那么再开一个线程好了，这样在处理复杂流程的时候也不会影响界面的流畅，用户体验也好。

以下是一段测试代码：

public class MainActivity extends Activity {  
      
        private Button btnTest;  
        private Button btnClear;  
        private TextView txtResult;  
        private Handler handler = null;  
      
        @Override  
        protected void onCreate(Bundle savedInstanceState) {  
            // StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()  
            // .detectDiskReads()  
            // .detectDiskWrites()  
            // .detectNetwork() // or .detectAll() for all detectable problems  
            // .penaltyLog()  
            // .build());  
            // StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder()  
            // .detectLeakedSqlLiteObjects()  
            // .detectLeakedClosableObjects()  
            // .penaltyLog()  
            // .penaltyDeath()  
            // .build());  
      
            super.onCreate(savedInstanceState);  
            setContentView(R.layout.activity_main);  
            btnTest = (Button) findViewById(R.id.btnTest);  
            btnClear = (Button) findViewById(R.id.btnClear);  
            txtResult = (TextView) findViewById(R.id.txtResult);  
            //  
            handler = new Handler() {  
                public void handleMessage(Message msg) {  
                    super.handleMessage(msg);  
                    if (msg.what == 0) {  
                        txtResult.append("\nBegin test >>\n");  
                    } else if (msg.what == 1) {  
                        txtResult.append(msg.obj.toString());  
                    } else if (msg.what == 2) {  
                        txtResult.append("\n<<End test\n");  
                    }  
                }  
            };  
            //  
            txtResult.setText("");  
            txtResult.setMovementMethod(ScrollingMovementMethod.getInstance());  
      
            btnTest.setOnClickListener(new View.OnClickListener() {  
      
                @Override  
                public void onClick(View v) {  
                    // doTest();  
                    doTestOnAndroid4();  
                }  
            });  
            btnClear.setOnClickListener(new View.OnClickListener() {  
      
                @Override  
                public void onClick(View v) {  
                    doClear();  
      
                }  
            });  
      
        }  
      
        protected void doClear() {  
            txtResult.setText("");  
      
        }  
      
        protected void doTest() {  
      
            String url = "http://www.baidu.com/";  
            txtResult.append("\nBegin test >>\n");  
            String text = "";  
            try {  
                text = Jsoup.connect(url).get().toString();  
            } catch (Exception e) {  
                e.printStackTrace();  
                // text = e.getMessage();  
            }  
            txtResult.append(text);  
            txtResult.append("\n<<End test\n");  
        }  
      
        protected void doTestOnAndroid4() {  
      
            new Thread(new Runnable() {  
                @Override  
                public void run() {  
                    Message m = new Message();  
                    m.what = 0;  
                    handler.sendMessage(m);  
                    //  
                    m = new Message();  
                    m.what = 1;  
                    String url = "http://www.baidu.com/";  
                    try {  
                        m.obj = Jsoup.connect(url).get().toString();  
                    } catch (Exception e) {  
                        e.printStackTrace();  
                        // m.obj = e.getMessage();  
                    }  
                    handler.sendMessage(m);  
                    //  
                    m = new Message();  
                    m.what = 2;  
                    handler.sendMessage(m);  
                }  
            }).start();  
      
        }  
      
    }

[http_developer.android.com_reference_android_os_StrictMode.html]: http://developer.android.com/reference/android/os/StrictMode.html