Android网络编程1

最近在自学Android开发，从这篇开始作为我学习android开发的笔记，来记录学习过程中遇到的问题点和其解决的方法；

Ui界面代码

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:paddingBottom="@dimen/activity_vertical_margin"
     android:paddingLeft="@dimen/activity_horizontal_margin"
     android:paddingRight="@dimen/activity_horizontal_margin"
     android:paddingTop="@dimen/activity_vertical_margin"
     tools:context="com.example.lidezhen.myapplication.MainActivity"
     android:orientation="vertical">
 <EditText
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     android:id="@+id/text1"
     android:hint="请是输入网址"/>
     <Button
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:text="打开"
             android:onClick="Onclick"/>
     <TextView
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:id="@+id/tv1"
         android:hint="这是源码"/>

 </LinearLayout>

界面后台代码

package com.example.lidezhen.myapplication;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class MainActivity extends AppCompatActivity {

    EditText et;
    TextView tv;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
         et= (EditText) findViewById(R.id.text1);
         tv= (TextView) findViewById(R.id.tv1);
//        if (android.os.Build.VERSION.SDK_INT > 9) {
//            StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
//            StrictMode.setThreadPolicy(policy);
//        }
    }
    public void Onclick(View v)
    {

        try {
            String path=et.getText().toString();

            URL url = new URL(path);
             HttpURLConnection con = (HttpURLConnection) url.openConnection();
            int code=con.getResponseCode();
            if (code==200)
            {

                InputStream stream = con.getInputStream();
                ByteArrayOutputStream os=new ByteArrayOutputStream();
                int len=-1;
                byte[] buff=new byte[1024];
                while ( (len=stream.read(buff))!=-1)
                {
                   os.write(buff,0,len);

                }
                tv.setText(os.toString());
            }
        } catch (Exception e) {
            Log.e("错误",e.toString());
        }

    }
}编译并执行程序

　　程序报错

07-20 02:30:00.361 15820-15820/com.example.lidezhen.myapplication E/错误: android.os.NetworkOnMainThreadException

错误原因：Android在4.0之前的版本 支持在主线程中访问网络，但是在4.0以后对这部分程序进行了优化，也就是说访问网络的代码不能写在主线程中了（我的虚拟机是android6.0的）

错误解决方法1：

在onCreate方法中添加如下代码

 if (android.os.Build.VERSION.SDK_INT > 9) {
            StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
           StrictMode.setThreadPolicy(policy);
        }

方法2：在点击事件里面添加多线程

public void Onclick(View v)
    {
        new Thread() {
            @Override
            public void run() {
                try {
                    String path=et.getText().toString();

                    URL url = new URL(path);
                    HttpURLConnection con = (HttpURLConnection) url.openConnection();
                    int code=con.getResponseCode();
                    if (code==200)
                    {

                        InputStream stream = con.getInputStream();
                        ByteArrayOutputStream os=new ByteArrayOutputStream();
                        int len=-1;
                        byte[] buff=new byte[1024];
                        while ( (len=stream.read(buff))!=-1)
                        {
                            os.write(buff,0,len);

                        }
                        tv.setText(os.toString());
                    }
                } catch (Exception e) {
                    Log.e("错误",e.toString());
                }

            }
        }.start();

程序执行成功

这样开新线程后程序还是报错

07-20 02:49:12.203 32712-707/com.example.lidezhen.myapplication E/错误: android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

意思就是新的线程不能操作界面控件

解决方法：添加handeler

package com.example.lidezhen.myapplication;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class MainActivity extends AppCompatActivity {

    EditText et;
    TextView tv;
    @Override
            protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
         et= (EditText) findViewById(R.id.text1);
         tv= (TextView) findViewById(R.id.tv1);

//       if (android.os.Build.VERSION.SDK_INT > 9) {
//            StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
//           StrictMode.setThreadPolicy(policy);
//        }
    }
    public void Onclick(View v)
    {

        new Thread() {
            @Override
            public void run() {
                try {

                    String path=et.getText().toString();
                    URL url = new URL(path);
                    HttpURLConnection con = (HttpURLConnection) url.openConnection();
                    int code=con.getResponseCode();
                    if (code==200)
                    {

                        InputStream stream = con.getInputStream();
                        ByteArrayOutputStream os=new ByteArrayOutputStream();
                        int len=-1;
                        byte[] buff=new byte[1024];
                        while ( (len=stream.read(buff))!=-1)
                        {
                            os.write(buff,0,len);

                        }
//                        tv.setText(os.toString());
                        Message msg=new Message();
                        msg.obj=os.toString();
                        handler.sendMessage(msg);
                    }
                } catch (Exception e) {
                    Log.e("错误",e.toString());
                }

            }
        }.start();

    }
   Handler handler=new Handler(){
       public void handleMessage(Message msg) {
           String s=(String)msg.obj;
         tv.setText(s);
       }

   };

}

这样就不会再报异常