android studio

by Dost Muhammad Shah on Electronics

Fixing “Unknown Kotlin JVM Target: 21” Error in Flutter

Recently, I faced this annoying issue while building a Flutter project:

FAILURE: Build failed with an exception.

What went wrong:
Could not determine the dependencies of task ':#####:compileDebugKotlin'.
Unknown Kotlin JVM target: 21

No matter what I tried, setting the JDK version for Gradle in Android Studio didn’t work. Running flutter doctor kept showing that the JDK version was 21.

Here’s what I found out:

  • Flutter was using the JDK bundled with Android Studio (jbr directory), which is JDK 21.
  • The problem is that Kotlin’s JVM doesn’t support JDK 21 yet.

The Solution:

I finally came across a fix that worked! You need to explicitly tell Flutter to use a different JDK version. Here’s how to do it:

  1. Find the path to an older JDK version (like JDK 18) on your system.
  2. Run this command in your terminal:
    flutter config –jdk-dir <dir> Replace with the actual path to your JDK installation.
  3. Run flutter doctor again to confirm that Flutter is now using the correct JDK.
  4. Restart Android Studio and rebuild your project.


Why This Works:

By default, Flutter uses the JDK bundled with Android Studio. This command forces Flutter to use the JDK version you specify, avoiding the compatibility issue with JDK 21.

Key Tip:


If you’re using Kotlin with Flutter, stick to JDK versions like 18 or 19 until Kotlin adds support for JDK 21.

Hopefully, this helps someone else struggling with the same issue! If you’ve faced a similar problem or have a different solution, let me know! 😊

 
by Dost Muhammad Shah on Android, Coding

Android: Updating the text of Toast message instantly

In my app,I wanted to show the number of taps to be made to accomplish a task, for this purpose i used Toast class , I used Toast.makeText to show the text. problem is that I couldn’t change the text or make it hide quickly if new text was to be shown. Android would queue all the makeText requests.

I wanted to have a solution to be able to change the text or be able to cancel the previous toast without waiting for it to finish. While Looking for solution I found this class called Boast by a StackOverFlow user Richard Le Mesurier. The Boast class accomplishes exactly what I needed.

The trick is to keep track of the last Toast that was shown, and to cancel that one.

What Richard Le Mesurier have done is to create a Toast wrapper, that contains a static reference to the last Toast displayed.

When I need to show a new one, I first cancel the static reference, before showing the new one (and saving it in the static).

Here’s full code of the Boast wrapper Richard Le Mesurier made – it mimics enough of the Toast methods for me to use it.

By default the Boast will cancel the previous one, so you don’t build up a queue of Toasts waiting to be displayed.

This should be a direct drop-in replacement for Toast in most use cases. for example

 mBoast.makeText(this,"your text",Duration).show();
import android.annotation.SuppressLint;
import android.content.Context;
import android.content.res.Resources;
import android.widget.Toast;

/**
 * {@link Toast} decorator allowing for easy cancellation of notifications. Use
 * this class if you want subsequent Toast notifications to overwrite current
 * ones. </p>
 *
 * By default, a current {@link Boast} notification will be cancelled by a
 * subsequent notification. This default behaviour can be changed by calling
 * certain methods like {@link #show(boolean)}.
 */
public class Boast
{
    /**
     * Keeps track of certain {@link Boast} notifications that may need to be cancelled.
     * This functionality is only offered by some of the methods in this class.
     */
    private volatile static Boast globalBoast = null;

    // ////////////////////////////////////////////////////////////////////////////////////////////////////////

    /**
     * Internal reference to the {@link Toast} object that will be displayed.
     */
    private Toast internalToast;

    // ////////////////////////////////////////////////////////////////////////////////////////////////////////

    /**
     * Private constructor creates a new {@link Boast} from a given
     * {@link Toast}.
     *
     * @throws NullPointerException
     *         if the parameter is <code>null</code>.
     */
    private Boast(Toast toast)
    {
        // null check
        if (toast == null)
        {
            throw new NullPointerException(
                    "Boast.Boast(Toast) requires a non-null parameter.");
        }

        internalToast = toast;
    }

    // ////////////////////////////////////////////////////////////////////////////////////////////////////////

    /**
     * Make a standard {@link Boast} that just contains a text view.
     *
     * @param context
     *        The context to use. Usually your {@link android.app.Application}
     *        or {@link android.app.Activity} object.
     * @param text
     *        The text to show. Can be formatted text.
     * @param duration
     *        How long to display the message. Either {@link #LENGTH_SHORT} or
     *        {@link #LENGTH_LONG}
     */
    @SuppressLint("ShowToast")
    public static Boast makeText(Context context, CharSequence text,
                                 int duration)
    {
        return new Boast(Toast.makeText(context, text, duration));
    }

    /**
     * Make a standard {@link Boast} that just contains a text view with the
     * text from a resource.
     *
     * @param context
     *        The context to use. Usually your {@link android.app.Application}
     *        or {@link android.app.Activity} object.
     * @param resId
     *        The resource id of the string resource to use. Can be formatted
     *        text.
     * @param duration
     *        How long to display the message. Either {@link #LENGTH_SHORT} or
     *        {@link #LENGTH_LONG}
     *
     * @throws Resources.NotFoundException
     *         if the resource can't be found.
     */
    @SuppressLint("ShowToast")
    public static Boast makeText(Context context, int resId, int duration)
            throws Resources.NotFoundException
    {
        return new Boast(Toast.makeText(context, resId, duration));
    }

    /**
     * Make a standard {@link Boast} that just contains a text view. Duration
     * defaults to {@link #LENGTH_SHORT}.
     *
     * @param context
     *        The context to use. Usually your {@link android.app.Application}
     *        or {@link android.app.Activity} object.
     * @param text
     *        The text to show. Can be formatted text.
     */
    @SuppressLint("ShowToast")
    public static Boast makeText(Context context, CharSequence text)
    {
        return new Boast(Toast.makeText(context, text, Toast.LENGTH_SHORT));
    }

    /**
     * Make a standard {@link Boast} that just contains a text view with the
     * text from a resource. Duration defaults to {@link #LENGTH_SHORT}.
     *
     * @param context
     *        The context to use. Usually your {@link android.app.Application}
     *        or {@link android.app.Activity} object.
     * @param resId
     *        The resource id of the string resource to use. Can be formatted
     *        text.
     *
     * @throws Resources.NotFoundException
     *         if the resource can't be found.
     */
    @SuppressLint("ShowToast")
    public static Boast makeText(Context context, int resId)
            throws Resources.NotFoundException
    {
        return new Boast(Toast.makeText(context, resId, Toast.LENGTH_SHORT));
    }

    // ////////////////////////////////////////////////////////////////////////////////////////////////////////

    /**
     * Show a standard {@link Boast} that just contains a text view.
     *
     * @param context
     *        The context to use. Usually your {@link android.app.Application}
     *        or {@link android.app.Activity} object.
     * @param text
     *        The text to show. Can be formatted text.
     * @param duration
     *        How long to display the message. Either {@link #LENGTH_SHORT} or
     *        {@link #LENGTH_LONG}
     */
    public static void showText(Context context, CharSequence text, int duration)
    {
        Boast.makeText(context, text, duration).show();
    }

    /**
     * Show a standard {@link Boast} that just contains a text view with the
     * text from a resource.
     *
     * @param context
     *        The context to use. Usually your {@link android.app.Application}
     *        or {@link android.app.Activity} object.
     * @param resId
     *        The resource id of the string resource to use. Can be formatted
     *        text.
     * @param duration
     *        How long to display the message. Either {@link #LENGTH_SHORT} or
     *        {@link #LENGTH_LONG}
     *
     * @throws Resources.NotFoundException
     *         if the resource can't be found.
     */
    public static void showText(Context context, int resId, int duration)
            throws Resources.NotFoundException
    {
        Boast.makeText(context, resId, duration).show();
    }

    /**
     * Show a standard {@link Boast} that just contains a text view. Duration
     * defaults to {@link #LENGTH_SHORT}.
     *
     * @param context
     *        The context to use. Usually your {@link android.app.Application}
     *        or {@link android.app.Activity} object.
     * @param text
     *        The text to show. Can be formatted text.
     */
    public static void showText(Context context, CharSequence text)
    {
        Boast.makeText(context, text, Toast.LENGTH_SHORT).show();
    }

    /**
     * Show a standard {@link Boast} that just contains a text view with the
     * text from a resource. Duration defaults to {@link #LENGTH_SHORT}.
     *
     * @param context
     *        The context to use. Usually your {@link android.app.Application}
     *        or {@link android.app.Activity} object.
     * @param resId
     *        The resource id of the string resource to use. Can be formatted
     *        text.
     *
     * @throws Resources.NotFoundException
     *         if the resource can't be found.
     */
    public static void showText(Context context, int resId)
            throws Resources.NotFoundException
    {
        Boast.makeText(context, resId, Toast.LENGTH_SHORT).show();
    }

    // ////////////////////////////////////////////////////////////////////////////////////////////////////////

    /**
     * Close the view if it's showing, or don't show it if it isn't showing yet.
     * You do not normally have to call this. Normally view will disappear on
     * its own after the appropriate duration.
     */
    public void cancel()
    {
        internalToast.cancel();
    }

    /**
     * Show the view for the specified duration. By default, this method cancels
     * any current notification to immediately display the new one. For
     * conventional {@link Toast#show()} queueing behaviour, use method
     * {@link #show(boolean)}.
     *
     * @see #show(boolean)
     */
    public void show()
    {
        show(true);
    }

    /**
     * Show the view for the specified duration. This method can be used to
     * cancel the current notification, or to queue up notifications.
     *
     * @param cancelCurrent
     *        <code>true</code> to cancel any current notification and replace
     *        it with this new one
     *
     * @see #show()
     */
    public void show(boolean cancelCurrent)
    {
        // cancel current
        if (cancelCurrent && (globalBoast != null))
        {
            globalBoast.cancel();
        }

        // save an instance of this current notification
        globalBoast = this;

        internalToast.show();
    }

}
 
by Dost Muhammad Shah on Android, Coding

make your android app boot at device start-up

If you want your app to start-up automatically when Android boots up you need to the following

#1: add the following to your android manifest file


<receiver android:enabled="true" android:name=".BootUpReceiver"
android:permission="android.permission.RECEIVE_BOOT_COMPLETED">
<intent-filter>
<action android:name="android.intent.action.BOOT_COMPLETED" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</receiver>
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />

view raw

gistfile1.xml

hosted with ❤ by GitHub

This will register for a boot complete receiver event and ask for its permission.

#2 Add a the following java class


public class BootUpReceiver extends BroadcastReceiver{
@Override
public void onReceive(Context context, Intent intent) {
Intent i = new Intent(context, MyActivity.class);
i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(i);
}
}

view raw

BootUpReceiver.java

hosted with ❤ by GitHub

 
by Dost Muhammad Shah on Android, Coding

How to filter logcat in Android Studio?

In logcat of Android Studio there is usually too much output, sometimes a developer would want to filter out these results so that he only gets logs from the application he is debugging. This can be achieved by the following method.
On the left side (right next to the tabs) is an icon with green arrows – it can be toggled on/off to display only logcat from the process selected in the list 🙂

aJJJa

UPDATE:
as of android studio ver 0.4.5 u will get messages from the app that is running only by default. Log cat has a new option (ON by default) which creates an application filter automatically such that only the launched application’s output is shown