子线程网络图片查看器和Handler消息处理器

1. Android not Responding(应用程序无响应) 阻塞了主线程 ANR异常

异常:

CalledFromWrongThreadException: Only theoriginal thread that created a view hierarchy can touch its views.

只有原始的线程(主线程, ui线程)才能修改view对象.

在子线程中修改view的显示状态, 会报上面异常.

2.


3.代码

因为是内部类，所以子线程可以用到主线程创建的handle

public class MainActivity extends Activity implements OnClickListener {

private static final String TAG = "MainActivity";
protected static final int ERROR = 1;
private EditText etUrl;
private ImageView ivIcon;
private final int SUCCESS = 0;

private Handler handler = new Handler() {

/**
* 接收消息
*/
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);

Log.i(TAG, "what = " + msg.what);
if(msg.what == SUCCESS) {	// 当前是访问网络, 去显示图片，可用于判断是哪个线程发的信息
ivIcon.setImageBitmap((Bitmap) msg.obj);		// 设置imageView显示的图片
} else if(msg.what == ERROR) {
Toast.makeText(MainActivity.this, "抓去失败", 0).show();
}
}
};

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

ivIcon = (ImageView) findViewById(R.id.iv_icon);
etUrl = (EditText) findViewById(R.id.et_url);

findViewById(R.id.btn_submit).setOnClickListener(this);
}

@Override
public void onClick(View v) {
final String url = etUrl.getText().toString();

new Thread(new Runnable() {

@Override
public void run() {
Bitmap bitmap = getImageFromNet(url);

//				ivIcon.setImageBitmap(bitmap);		// 设置imageView显示的图片
if(bitmap != null) {
Message msg = new Message();
msg.what = SUCCESS;            //what可用于判断是哪个线程发的信息
msg.obj = bitmap;
handler.sendMessage(msg);
} else {
Message msg = new Message();
msg.what = ERROR;
handler.sendMessage(msg);
}
}}).start();

}
//-------------------------------------------------------子线程与主线程通信-------上----------------------------------
/**
* 根据url链接取网络抓去图片返回
* @param url
* @return url对应的图片
*/
private Bitmap getImageFromNet(String url) {
HttpURLConnection conn = null;
try {
URL mURL = new URL(url);	// 创建一个url对象

// 得到http的连接对象
conn = (HttpURLConnection) mURL.openConnection();

conn.setRequestMethod("GET");		// 设置请求方法为Get
conn.setConnectTimeout(10000);		// 设置连接服务器的超时时间, 如果超过10秒钟, 没有连接成功, 会抛异常
conn.setReadTimeout(5000);		// 设置读取数据时超时时间, 如果超过5秒, 抛异常

conn.connect();		// 开始链接

int responseCode = conn.getResponseCode(); // 得到服务器的响应码
if(responseCode == 200) {
// 访问成功
InputStream is = conn.getInputStream();	// 获得服务器返回的流数据

Bitmap bitmap = BitmapFactory.decodeStream(is); // 根据 流数据 创建一个bitmap位图对象

return bitmap;
} else {
Log.i(TAG, "访问失败: responseCode = " + responseCode);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if(conn != null) {
conn.disconnect();		// 断开连接
}
}
return null;
}
}