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
Android网络编程1
 

  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

Android网络编程1

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

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