Android网络编程1

2022-10-19 20:02:39

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

码农公寓

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