My Activity正在使用带有while循环的Runnable线程的onCreate（）。这是代码：
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_post_user_registration);
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
SharedPreferences.Editor editor = sp.edit();
//Some Async task here
final File destFile = new File(filesDir, sp.getString(Constants.SharedPreferences.USER_ID,null)+ Constants.S3Bucket.IMAGE_EXTENSION);
final File downFile = new File(filesDir, Constants.S3Bucket.USER_DIRECTORY + sp.getString(Constants.SharedPreferences.USER_ID,null)+ Constants.S3Bucket.IMAGE_EXTENSION);
Runnable myRunnable = new Runnable() {
@Override
public void run() {
Log.v(LOG_TAG,"S3 file profile exists "+downFile.getAbsolutePath()+" "+downFile.exists());
while(!downFile.exists()){
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
Log.e(LOG_TAG,"Error",e);
}
Log.v(LOG_TAG,"Inside while loop");
}
Log.v(LOG_TAG,"S3 file profile exists after while "+downFile.getAbsolutePath()+" "+downFile.exists());
Intent intent = new Intent(getApplicationContext(), MainActivity.class);
startActivity(intent);
finish();
}
};
Thread myThread = new Thread(myRunnable);
myThread.start();
}
该线程基本上检查由AWS服务创建的downFile。我的活动一直在运行，控件不会在循环时进入。该条件第一次为真，之后控制既不进入循环也不进入。正确记录while循环之前的语句。所以，基本上MainActivity并没有开始。
这是一个错误的线程实现吗？我不明白这里发生了什么。
如果我停止应用程序并再次运行它，则条件现在为false，因此控件在循环时不会进入，但下一个Activity正确加载。
答案 0 :(得分：1)
使用AsyncTask来处理你正在做的事情，你不必陷入无休止的循环中。
在此处使用它们的完整说明：ImageJ
我已经在服务器上为grabbinf图像实现了一个:(下面的代码片段） http://www.compiletimeerror.com/2013/01/why-and-how-to-use-asynctask.html
甚至Android都有一个关于在这里使用它们的教程： http://wlgfx.com/programming/tcp-android-client-and-server-code/
最后一个链接的例子：
private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
protected Long doInBackground(URL... urls) {
int count = urls.length;
long totalSize = 0;
for (int i = 0; i < count; i++) {
totalSize += Downloader.downloadFile(urls[i]);
publishProgress((int) ((i / (float) count) * 100));
// Escape early if cancel() is called
if (isCancelled()) break;
}
return totalSize;
}
protected void onProgressUpdate(Integer... progress) {
setProgressPercent(progress[0]);
}
protected void onPostExecute(Long result) {
showDialog("Downloaded " + result + " bytes");
}
}
我自己使用AsynTask ...
public class GetImageFromServer extends AsyncTask<Void, Void, Bitmap> {
private final String tag = "WLGFX-AsyncBitmap";
private Context context;
private ImageView imageView;
private int width;
private int height;
GetImageFromServer(Context ctx, ImageView view) {
context = ctx;
imageView = view;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
imageView.setImageBitmap(null);
width = imageView.getWidth();
height = imageView.getHeight();
}
@Override
protected void onPostExecute(Bitmap bitmap) {
super.onPostExecute(bitmap);
imageView.setImageBitmap(bitmap);
Log.d(tag, "Bitmap: " +
"(" + bitmap.getWidth() +
"," + bitmap.getHeight() + ")" +
" " + bitmap.getByteCount());
}
@Override
protected Bitmap doInBackground(Void... voids) {
String head = "GSIF";
byte[] header_data = head.getBytes();
try {
InetAddress address = InetAddress.getByName(Global.server_host);
Socket socket = new Socket(address, Global.tcp_port);
OutputStream out = socket.getOutputStream();
out.write(header_data);
byte[] dim = new byte[2];
dim[0] = (byte)(width >> 8);
dim[1] = (byte)width;
out.write(dim);
dim[0] = (byte)(height >> 8);
dim[1] = (byte)(height);
out.write(dim);
byte[] length = new byte[4];
readSocketBytes(socket, length);
int size = (length[0] & 255) << 24 |
(length[1] & 255) << 16 |
(length[2] & 255)<< 8 |
length[3] & 255;
byte[] image_data = new byte[size];
readSocketBytes(socket, image_data);
Bitmap bitmap = BitmapFactory.decodeByteArray(image_data, 0, size);
socket.close();
return bitmap;
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
private void readSocketBytes(Socket socket, byte[] data) throws IOException {
int length = data.length;
InputStream in = socket.getInputStream();
int position = 0;
while (position < length) {
int count = in.read(data, position, length - position);
if (count > 0) position += count;
else throw new IOException();
}
}
}
答案 1 :(得分：1)
尝试使用Handler类而不是Thread类。它是为此而做的。
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_post_user_registration);
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
SharedPreferences.Editor editor = sp.edit();
//Some Async task here
final File destFile = new File(filesDir, sp.getString(Constants.SharedPreferences.USER_ID,null)+ Constants.S3Bucket.IMAGE_EXTENSION);
final File downFile = new File(filesDir, Constants.S3Bucket.USER_DIRECTORY + sp.getString(Constants.SharedPreferences.USER_ID,null)+ Constants.S3Bucket.IMAGE_EXTENSION);
Runnable myRunnable = new Runnable() {
@Override
public void run() {
Log.v(LOG_TAG,"S3 file profile exists "+downFile.getAbsolutePath()+" "+downFile.exists());
while(!downFile.exists()){
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
Log.e(LOG_TAG,"Error",e);
}
Log.v(LOG_TAG,"Inside while loop");
}
Log.v(LOG_TAG,"S3 file profile exists after while "+downFile.getAbsolutePath()+" "+downFile.exists());
Intent intent = new Intent(getApplicationContext(), MainActivity.class);
startActivity(intent);
finish();
}
};
Handler handler = new Handler();
handler.post(myRunnable);
}