I have a thread like:
startButton.setChangeListener(new FieldChangeListener() {
public void fieldChanged(Field arg0, int arg1) {
Thread thread = new Thread(){
public void run() {
uploadFile();
}
};
thread.start();
}
//});
});
The uploadFile method contains the line label_up_result.setText(result); which causes an IllegalStateException.
label_up_result is defined like: final LabelField label_up_result=new LabelField("", LabelField.FIELD_LEFT);
What can be the problem ? How can I fix it ?
The problem is probably that you are trying to update the UI from a worker thread. There are two approaches. You can synchronize on the event lock:
synchronized(UiApplication.getUiApplication().getEventLock())) {
label_up_result.setText(result);
}
or you can create a Runnable to execute on the UI thread:
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
label_up_result.setText(result);
}
});
I don't know about blackberry, but usually you need to perform the ui-actions in the ui-thread. SwingUtilities.invokeLater provides that functionality in JavaSE, http://www.java2s.com/Code/Java/Swing-JFC/Swinginvokelater.htm
Related
I'm trying to use Tesseract in flutter using the following package https://github.com/arrrrny/tesseract_ocr
I've download the app and run in.
The problem is that the extractText hangs the UI.
Looking at the Java code:
Thread t = new Thread(new Runnable() {
public void run() {
baseApi.setImage(tempFile);
recognizedText[0] = baseApi.getUTF8Text();
baseApi.end();
}
});
t.start();
try { t.join(); } catch (InterruptedException e) { e.printStackTrace(); }
result.success(recognizedText[0]);
I can see that it is running on a new thread, so I expect it not to hang the app, but it still does.
I found this example:
new Handler(Looper.getMainLooper()).post(new Runnable() {
#Override
public void run() {
// Call the desired channel message here.
baseApi.setImage(tempFile);
recognizedText[0] = baseApi.getHOCRText(0);
baseApi.end();
result.success(recognizedText[0]);
}
});
from https://flutter.dev/docs/development/platform-integration/platform-channels#channels-and-platform-threading
but it also hangs the UI.
The docs also say
**Channels and Platform Threading**
Invoke all channel methods on the platform’s main thread when writing code on the platform side.
Can someone clarify this sentence?
According to Richard Heap answer, I tried to call a method from native to dart, passing the result:
Dart side:
_channel.setMethodCallHandler((call) {
print(call);
switch (call.method) {
case "extractTextResult":
final String result = call.arguments;
print(result);
}
var t;
return t;
});
Java side:
channel.invokeMethod("extractTextResult","hello");
if I call this method from the main thread, this works fine, but then the thread is blocking.
If I do
Thread t = new Thread(new Runnable() {
public void run() {
channel.invokeMethod("extractTextResult","test1231231");
}
});
t.start();
result.success("tst"); // return immediately
Then the app crashes with the following message:
I also tried:
Thread t = new Thread(new Runnable() {
public void run() {
new Handler(Looper.getMainLooper()).post(new Runnable() {
#Override
public void run() {
// Call the desired channel message here.
baseApi.setImage(tempFile);
recognizedText[0] = baseApi.getHOCRText(0);
baseApi.end();
result.success(recognizedText[0]);
// channel.invokeMethod("extractTextResult", "test1231231");
}
});
}
});
t.start();
result.success("tst");
which is what I understand that Richard Heap last comment meant, but It still hangs the ui.
I had the same Issue and fixed it with a MethodCallWrapper in TesseractOcrPlugin.java
This Code works for me (no Dart-code change is needed):
package io.paratoner.tesseract_ocr;
import com.googlecode.tesseract.android.TessBaseAPI;
import android.os.Handler;
import android.os.Looper;
import android.os.AsyncTask;
import java.io.File;
import io.flutter.plugin.common.MethodCall;
import io.flutter.plugin.common.MethodChannel;
import io.flutter.plugin.common.MethodChannel.MethodCallHandler;
import io.flutter.plugin.common.MethodChannel.Result;
import io.flutter.plugin.common.PluginRegistry.Registrar;
/** TesseractOcrPlugin */
public class TesseractOcrPlugin implements MethodCallHandler {
private static final int DEFAULT_PAGE_SEG_MODE = TessBaseAPI.PageSegMode.PSM_SINGLE_BLOCK;
/** Plugin registration. */
public static void registerWith(Registrar registrar) {
final MethodChannel channel = new MethodChannel(registrar.messenger(), "tesseract_ocr");
channel.setMethodCallHandler(new TesseractOcrPlugin());
}
// MethodChannel.Result wrapper that responds on the platform thread.
private static class MethodResultWrapper implements Result {
private Result methodResult;
private Handler handler;
MethodResultWrapper(Result result) {
methodResult = result;
handler = new Handler(Looper.getMainLooper());
}
#Override
public void success(final Object result) {
handler.post(new Runnable() {
#Override
public void run() {
methodResult.success(result);
}
});
}
#Override
public void error(final String errorCode, final String errorMessage, final Object errorDetails) {
handler.post(new Runnable() {
#Override
public void run() {
methodResult.error(errorCode, errorMessage, errorDetails);
}
});
}
#Override
public void notImplemented() {
handler.post(new Runnable() {
#Override
public void run() {
methodResult.notImplemented();
}
});
}
}
#Override
public void onMethodCall(MethodCall call, Result rawResult) {
Result result = new MethodResultWrapper(rawResult);
if (call.method.equals("extractText")) {
final String tessDataPath = call.argument("tessData");
final String imagePath = call.argument("imagePath");
String DEFAULT_LANGUAGE = "eng";
if (call.argument("language") != null) {
DEFAULT_LANGUAGE = call.argument("language");
}
calculateResult(tessDataPath, imagePath, DEFAULT_LANGUAGE, result);
} else {
result.notImplemented();
}
}
private void calculateResult(final String tessDataPath, final String imagePath, final String language,
final Result result) {
new AsyncTask<Void, Void, Void>() {
#Override
protected Void doInBackground(Void... params) {
final String[] recognizedText = new String[1];
final TessBaseAPI baseApi = new TessBaseAPI();
baseApi.init(tessDataPath, language);
final File tempFile = new File(imagePath);
baseApi.setPageSegMode(DEFAULT_PAGE_SEG_MODE);
baseApi.setImage(tempFile);
recognizedText[0] = baseApi.getUTF8Text();
baseApi.end();
result.success(recognizedText[0]);
return null;
}
#Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
}
}.execute();
}
}
By using join you're making the main thread wait for the background thread, blocking it. You have to remove the join and return a result immediately.
So, how do you return the ocr result, which won't be available immediately. When it becomes available, you then call a method from native to dart, passing the result. At the dart end, you then handle the result as any async event.
The point of the last paragraph of your question is that your result will become available on your background thread, so you'd want to call the native to dart method there. You can't. You have to post the method call code to the main looper - you already show some code for posting to the main looper which you can use as an example.
Based on Richard Heap answer I came up with this:
Dart code:
_channel.setMethodCallHandler((call) {
switch (call.method) {
case "extractTextResult":
final String result = call.arguments;
print(result);
}
var t;
return t;
});
Java code:
Thread t = new Thread(new Runnable() {
public void run() {
baseApi.setImage(tempFile);
recognizedText[0] = baseApi.getHOCRText(0);
baseApi.end();
new Handler(Looper.getMainLooper()).post(new Runnable() {
#Override
public void run() {
channel.invokeMethod("extractTextResult", recognizedText[0]);
}
});
}
});
t.start();
result.success("tst");
explain:
This code will run the Java extractText in a separate thread, and when the result is ready it will hopp back to the ui thread with the call to Looper.getMainLooper() which will then send the message back to the Dart side which must receive the message on the ui thread, which is what this message means:
**Channels and Platform Threading**
Invoke all channel methods on the platform’s main thread when writing code on the platform side.
NOTE on the Dart side, this is still incomplete example since you then need to report to the ui that a message received, this can be done with a Completer, which is used to create and complete a future
At the end of your method channel just return the response back to dart side
Add this line at the end of method channel result.success(true)
full example
override fun configureFlutterEngine(#NonNull flutterEngine: FlutterEngine) {
super.configureFlutterEngine(flutterEngine)
MethodChannel(
flutterEngine.dartExecutor.binaryMessenger,
"method-channel"
).setMethodCallHandler { call, result ->
if (call.method == "getFirebaseAppCheckDebugToken") {
...
result.success(true) // just add this line
}
}
}```
I interested in one interesting task. I have UI in JavaFx with another thread which updates UI. I started updates from Platform.runLater. Code:
private void startUpdateDaemon() {
updateUserStatus();
updateTable();
}
private void startUpdateDaemonTask() {
Task task = new Task<Void>() {
#Override
protected Void call() throws Exception {
while (true) {
Platform.runLater(() -> {
startUpdateDaemon();
});
Thread.sleep(1000);
}
}
};
Thread th = new Thread(task);
th.setDaemon(true);
th.start();
}
#Override
public void initialize(URL location, ResourceBundle resources) {
startUpdateDaemonTask();
}
Also I have place in another class where I updates UI:
private void startUpdateDaemonTask() {
Task task = new Task<Void>() {
#Override
protected Void call() throws Exception {
while (true) {
Platform.runLater(new Runnable() {
#Override
public void run() {
updateGameStatus();
}
});
Thread.sleep(1000);
}
}
};
Thread th = new Thread(task);
th.setDaemon(true);
th.start();
}
So, finally I have two places with call "Platform.runLater" and different methods inside.
My question is Can I create only "one" method with one time call "Platform.runLater" and send to this method different methods which will be call ?? May be I can write finish method with consumers and send to him methods 'startUpdateDaemon()' and 'updateGameStatus()'?
Thanks a lot.
You can add a Runnable parameter to your method. This parameter is given to you Platform.runLater:
private void startUpdateDaemonTask(Runnable runner) {
Task task = new Task<Void>() {
#Override
protected Void call() throws Exception {
while (true) {
Platform.runLater(runner);
Thread.sleep(1000);
}
}
};
Thread th = new Thread(task);
th.setDaemon(true);
th.start();
}
Now you can invoke this method with your method references:
startUpdateDaemonTask(this::startUpdateDaemon);
startUpdateDaemonTask(this::updateGameStatus);
I am trying to run a thread in background with while(true) condition, and not using any join after the thread so that it continue running the main thread. But what I am observing is only while loop is running and it is not switching to main thread. please help me find the issue. This is Groovy code.
public static void main(args) {
Thread.start {
while (true) {
long sleepMillis = 2000
System.out.println("inside async block")
Thread.sleep(sleepMillis)
}
}
//main func code goes here
}
Please give me pointers to the issue.
Here You go:
public class Lol {
public static void main(String[] args) {
def t = new Thread(new Runnable() {
public void run() {
while(true) {
println 'lol'
Thread.sleep(500)
}
}
}).start()
println 'other'
}
}
I am trying to implement a program where I want different Components to blink at different speeds. I am using threads. But its not working.
How can I implement this.
This is the void run function in the class that implements runnable
public void run()
{
try
{
while(true)
{
Thread.sleep(1000);
if(isVisible()==true)
{
setVisible(false);
}
else
{
setVisible(true);
}
repaint();
}
}
catch(InterruptedException e)
{
}
}
}
and this is the class (its in a paint component of the main JPanel)where I call the threads-
{
cars[i]=new Car(color, xLocation, yLocation, speed, type, i, widthController, heightController);
cars[i].setBounds(widthController+(xLocation*50)+10, heightController+(yLocation*50)+10, 30, 30);
add(cars[i]);
threads[i]=new Thread(cars[i]);
threads[i].start();
}
cars is an array of JComponents of which void run is part of.
Thanks
With Swing, all operations that affect visible components should be run on the AWT-EventQueue. This is a dedicated thread for Input/Output operations as well as drawing and component operations. My recommendation is to use a swing timer for your run operation. The repaint call you made will call the paintCompnent method on the AWT-EventQueue. However you're changing the state of visibility on a seperate thread. This means that by the time the repaint call is made, it's possible the state has already changed to the previous value.
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JPanel;
import javax.swing.Timer;
//Rest of code above...
//This will execute the timer every 500 milliseconds
Timer aTimer = new Timer(500, new ActionListener() {
#Override
public void actionPerformed(ActionEvent pE) {
aComponent.setVisible(!aComponent.isVisible());
}
});
aTimer.start();
Another option is that on each thread add this call:
//This should be added inside of your thread
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
aComponent.setVisible(!aComponent.isVisible());
}
});
Here's the answer I was alluding to in my comments:
public void run()
{
try
{
while(true)
{
Thread.sleep(1000);
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
setVisible(!isVisible());
}
}
});
}
catch(InterruptedException e)
{
}
Every time when my apps went to the layout that download image online, the device will hang and need to wait the download finish only can movable.
I did some researched. They recommend download it in another Thread. However, I not understand how to implement the download function in another Thread.
Here is my code to call the download image function.
Main.getUiApplication().invokeLater(new Runnable() {
public void run() {
for (j = 0; j < imagepath.length; j++) {
if (!imagepath[j].toString().equals("no picture")
&& Config_GlobalFunction.isConnected()) {
loader = new Util_LazyLoader(imagepath[j],
new Util_BitmapDowloadListener() {
public void ImageDownloadCompleted(
Bitmap bmp) {
imagebitmap[j] = bmp;
invalidate();
}
});
loader.run();
}
}
}
}, 500, false);
And the lazyloader
public class Util_LazyLoader implements Runnable {
String url = null;
Util_BitmapDowloadListener listener = null;
public Util_LazyLoader(String url, Util_BitmapDowloadListener listener) {
this.url = url;
this.listener = listener;
}
public void run() {
Bitmap bmpImage = getImageFromWeb(url);
listener.ImageDownloadCompleted(bmpImage);
}
private Bitmap getImageFromWeb(String url) {
HttpConnection connection = null;
InputStream inputStream = null;
EncodedImage bitmap;
byte[] dataArray = null;
try {
connection = (HttpConnection) (new ConnectionFactory())
.getConnection(url + Database_Webservice.ht_params)
.getConnection();
int responseCode = connection.getResponseCode();
if (responseCode == HttpConnection.HTTP_OK) {
inputStream = connection.openDataInputStream();
dataArray = IOUtilities.streamToBytes(inputStream);
}
} catch (Exception ex) {
} finally {
try {
inputStream.close();
connection.close();
} catch (Exception e) {
}
}
if (dataArray != null) {
bitmap = EncodedImage.createEncodedImage(dataArray, 0,
dataArray.length);
return bitmap.getBitmap();
} else {
return null;
}
}
}
I need help on it as I not familiar in networking.
So, the Util_LazyLoader is already well written to support background image downloads, because it implements the Runnable interface. You can start the download like this:
Util_LazyLoader loader =
new Util_LazyLoader(imagepath[j],
new Util_BitmapDowloadListener() {
public void ImageDownloadCompleted(final Bitmap bmp) {
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
imagebitmap[j] = bmp;
invalidate();
}
});
}
});
Thread backgroundWorker = new Thread(loader);
backgroundWorker.start();
instead of directly calling the loader.run() method yourself.
A Runnable class is just one that has a run() method. You give your Runnable loader object to a new Thread and tell it to start(). This will cause that Thread to execute the run() method in another thread, instead of the UI thread. As long as you don't run network operations on the UI thread, your app should not appear to the user to be frozen.
Note: in your original code, you have this:
Main.getUiApplication().invokeLater(new Runnable() {
public void run() {
You probably don't need that at all. If that code is being run from the main (UI) thread, then all that's doing is telling the app to invoke that locally-defined run() method, also on the UI thread. You do pass a 500 millisecond delay as well. Maybe you need that (?). If you just want it to run right away, though, get rid of the code above (invokeLater(new Runnable() { public void run() { ...). Just use the code I posted (at the top of this answer) to create the backgroundWorker and then call its start() method.
Also, take note of two things in my implementation:
1. I used the UiApplication.invokeLater() method once the bitmap has been received. After the network operation completes, the UI must be updated. But that should not be done on the background thread. So, you create a Runnable to run on the background thread, and then once the download is complete, you create another Runnable to update the UI:
public void run() {
imagebitmap[j] = bmp;
invalidate();
}
2. Because I create another Runnable, and use the bmp variable inside that Runnable, I must declare it as a final parameter. The compiler requires you to do that. Another option would be to use the event lock directly, instead of invokeLater():
public void ImageDownloadCompleted(Bitmap bmp) {
synchronized(UiApplication.getEventLock()) {
imagebitmap[j] = bmp;
invalidate();
}
}
Either should work for you.