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接着处理《Android 网络图片查看器》中出现的问题
使用添加子线程，修改原程序：
package com.wuyudong.imagesviewer; import java.io.InputStream; import java.net.HttpURLConnection; import java.net.MalformedURLException; import java.net.URL; import org.apache.http.HttpConnection; import android.os.Bundle; import android.app.Activity; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.text.TextUtils; import android.view.Menu; import android.view.View; import android.widget.EditText; import android.widget.ImageView; import android.widget.Toast; public class MainActivity extends Activity { private EditText et_path; private ImageView iv; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); et_path = (EditText) findViewById(R.id.et_path); iv = (ImageView) findViewById(R.id.iv); } public void click(View view) { final String path = et_path.getText().toString().trim(); if (TextUtils.isEmpty(path)) { Toast.makeText(this, "图片路径不能为空", 0).show(); } else { new Thread() { @Override public void run() { // 连接服务器get请求获取图片 try { URL url = new URL(path); // 根据url发送http的请求 HttpURLConnection conn = (HttpURLConnection) url .openConnection(); // 设置请求的方式 conn.setRequestMethod("GET"); conn.setConnectTimeout(5000); conn.setReadTimeout(5000); conn.setRequestProperty( "User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.101 Safari/537.36"); int code = conn.getResponseCode(); if (code == 200) { InputStream is = conn.getInputStream(); Bitmap bitmap = BitmapFactory.decodeStream(is); iv.setImageBitmap(bitmap); } else { Toast.makeText(MainActivity.this, "显示图片失败", 0) .show(); } } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); Toast.makeText(MainActivity.this, "访问获取图片失败", 0).show(); } } }.start(); } } }
运行项目后报错：
06-27 19:27:59.613: W/System.err(2471): android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
谁创建了view对象，谁才能动修改view。
代码：iv.setImageBitmap(bitmap);目的就是为了修改UI
也即是主线程才可以修改。为了控制多线程修改view同步问题而设定的
修改后的代码如下:
package com.wuyudong.imagesviewer; import java.io.InputStream; import java.net.HttpURLConnection; import java.net.MalformedURLException; import java.net.URL; import org.apache.http.HttpConnection; import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.app.Activity; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.text.TextUtils; import android.view.Menu; import android.view.View; import android.widget.EditText; import android.widget.ImageView; import android.widget.Toast; public class MainActivity extends Activity { protected static final int CHANGE_UI = 1; protected static final int ERROR = 2; private EditText et_path; private ImageView iv; // 1、主线程创建消息处理器 private Handler handler = new Handler() { public void handleMessage(android.os.Message msg) { if (msg.what == CHANGE_UI) { Bitmap bitmap = (Bitmap) msg.obj; iv.setImageBitmap(bitmap); } else if (msg.what == ERROR) { Toast.makeText(MainActivity.this, "访问获取图片失败", 0).show(); } }; }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); et_path = (EditText) findViewById(R.id.et_path); iv = (ImageView) findViewById(R.id.iv); } public void click(View view) { final String path = et_path.getText().toString().trim(); if (TextUtils.isEmpty(path)) { Toast.makeText(this, "图片路径不能为空", 0).show(); } else { new Thread() { @Override public void run() { // 连接服务器get请求获取图片 try { URL url = new URL(path); // 根据url发送http的请求 HttpURLConnection conn = (HttpURLConnection) url .openConnection(); // 设置请求的方式 conn.setRequestMethod("GET"); conn.setConnectTimeout(5000); conn.setReadTimeout(5000); conn.setRequestProperty( "User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.101 Safari/537.36"); // 得到服务器返回的响应码 int code = conn.getResponseCode(); if (code == 200) { InputStream is = conn.getInputStream(); Bitmap bitmap = BitmapFactory.decodeStream(is); // iv.setImageBitmap(bitmap); // TODO:告诉主线程一个消息：帮我更改界面，内容：bitmap Message msg = new Message(); msg.what = CHANGE_UI; msg.obj = bitmap; handler.sendMessage(msg); } else { // Toast.makeText(MainActivity.this, "显示图片失败", 0) // .show(); Message msg = new Message(); msg.what = ERROR; handler.sendMessage(msg); } } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); // Toast.makeText(MainActivity.this, "访问获取图片失败", // 0).show(); Message msg = new Message(); msg.what = ERROR; handler.sendMessage(msg); } } }.start(); } } }
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原文地址：http://www.cnblogs.com/wuyudong/p/5620466.html
