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
1 <?xml version="1.0" encoding="utf-8"?> 2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 3 xmlns:tools="http://schemas.android.com/tools" 4 android:layout_width="match_parent" 5 android:layout_height="match_parent" 6 android:paddingBottom="@dimen/activity_vertical_margin" 7 android:paddingLeft="@dimen/activity_horizontal_margin" 8 android:paddingRight="@dimen/activity_horizontal_margin" 9 android:paddingTop="@dimen/activity_vertical_margin" 10 tools:context="com.example.lidezhen.myapplication.MainActivity" 11 android:orientation="vertical"> 12 <EditText 13 android:layout_width="match_parent" 14 android:layout_height="wrap_content" 15 android:id="@+id/text1" 16 android:hint="请是输入网址"/> 17 <Button 18 android:layout_width="wrap_content" 19 android:layout_height="wrap_content" 20 android:text="打开" 21 android:onClick="Onclick"/> 22 <TextView 23 android:layout_width="match_parent" 24 android:layout_height="match_parent" 25 android:id="@+id/tv1" 26 android:hint="这是源码"/> 27 28 </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