android - 如何在android中使用asyncTask

Question

我是 android 的新手..我试图解决 networkonmainthreadexception，所以我使用了异步任务但仍然遇到相同的异常.. 出了什么问题？？这是我的 onCreate 方法

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    new Connection().execute();       
}

这是我的连接方式

private class Connection extends AsyncTask<Object, Object, Object>
{
    @Override
    protected void onPreExecute() {
        preExecuteLogin();
      }
    @Override
    protected Object doInBackground(Object... params) {
        // TODO Auto-generated method stub
        doInBackgroundLogin();
        return null;
    }


}

这是预执行方法

 public void preExecuteLogin()
{
    txtUserName=(EditText)this.findViewById(R.id.txtUsername);
    txtPassword=(EditText)this.findViewById(R.id.txtPassword);
    buttonLogin=(ImageButton)this.findViewById(R.id.buttonLogin);
}

这是我的 doInBackgroundLogin 方法

 public void doInBackgroundLogin()
{

    buttonLogin.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
        // TODO Auto-generated method stub

        if((txtUserName.getText().toString()).equals(txtPassword.getText().toString())){
                showToast("Login successfull");

                String link = "http://www.quinoid.com/project/AndroidXml/Login.php?username="
                               + txtUserName.getText().toString() + "&password=" + txtPassword.getText().toString();
                try {

                        JSONObject json = jParser.getJSONFromUrl(link);

                } catch (JSONException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                Intent myIntent = new Intent(MainActivity.this, secondpage.class);
                startActivity(myIntent); 
               } else{
                showToast("Invalid Login");
               }

        }
    });       
}

那么我究竟做错了什么？我的堆栈跟踪

02-11 03:17:38.797: E/AndroidRuntime(1324): FATAL EXCEPTION: main
02-11 03:17:38.797: E/AndroidRuntime(1324): Process: com.example.qwedd, PID: 1324
02-11 03:17:38.797: E/AndroidRuntime(1324): android.os.NetworkOnMainThreadException
02-11 03:17:38.797: E/AndroidRuntime(1324):     at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1145)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at java.net.InetAddress.lookupHostByName(InetAddress.java:385)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at java.net.InetAddress.getAllByName(InetAddress.java:214)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:137)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at com.example.connection.JSONParser.getJSONFromUrl(JSONParser.java:38)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at com.example.qwedd.MainActivity$2.onClick(MainActivity.java:68)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at android.view.View.performClick(View.java:4438)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at android.view.View$PerformClick.run(View.java:18422)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at android.os.Handler.handleCallback(Handler.java:733)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at android.os.Handler.dispatchMessage(Handler.java:95)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at android.os.Looper.loop(Looper.java:136)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at android.app.ActivityThread.main(ActivityThread.java:5017)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at java.lang.reflect.Method.invokeNative(Native Method)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at  java.lang.reflect.Method.invoke(Method.java:515)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
02-11 03:17:38.797: E/AndroidRuntime(1324):     at dalvik.system.NativeStart.main(Native Method)
02-11 03:22:38.957: I/Process(1324): Sending signal. PID: 1324 SIG: 9

Answer 1

其实你是

打电话

Toast.makeText 在 login() 方法中。

Toast 只能显示在 UI 线程上。

要么从 login() 方法中删除 Toast。

或者像这样调用 Toast

private void showToast(String msg){
    runOnUiThread(new Runnable() {          
        @Override
        public void run() {
            Toast.makeText(MainActivity.this, msg,Toast.LENGTH_LONG).show();    
        }
    }); 
}

完整的解决方案

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    txtUserName=(EditText)this.findViewById(R.id.txtUsername);
    txtPassword=(EditText)this.findViewById(R.id.txtPassword);
    buttonLogin=(ImageButton)this.findViewById(R.id.buttonLogin);

    buttonLogin.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
            new Connection().execute();   
        }
    });              
}

public void doInBackgroundLogin() {
    if((txtUserName.getText().toString()).equals(txtPassword.getText().toString())){
        showToast("Login successfull");

        String link = "http://www.quinoid.com/project/AndroidXml/Login.php?username="
                               + txtUserName.getText().toString() + "&password=" + txtPassword.getText().toString();
        try {    
            JSONObject json = jParser.getJSONFromUrl(link);
        } catch (JSONException e) {
            e.printStackTrace();
        }

        Intent myIntent = new Intent(MainActivity.this, secondpage.class);
        startActivity(myIntent); 
    } else{
        showToast("Invalid Login");
    }
}