Qt Android: How to call Toast.makeText from Java?

Carmoneer

You need to create a static instance of your main java class object and call the method that way. So in your 'JavaMain':

public class MyJavaMain extends QtActivity {

    // Singleton Instance
    public  static MyJavaMain mInstance;

    ...

    public MyJavaMain () {
        Log.d(QtApplication.QtTAG, "Java constructor called.");
        mInstance = this;
    }

    ...

    public static MyMethodCallToast(final String message) {
         mInstance.runOnUiThread(new Runnable() {
            public void run() {
               Toast.makeText(mInstance.getApplicationContext(),
                              message,
                              Toast.LENGTH_SHORT).show();
           }
        });
    }  
}

Hopefully that helps. Cheers!

Ibrahim

@Carmoneer Thanks, I get this error:

W/dalvikvm( 7847): Exception thrown (Ljava/lang/NullPointerException;) while throwing internal exception (Ljava/lang/NullPointerException;)
W/InputMethodManagerService(  589): Starting input on non-focused client com.android.internal.view.IInputMethodClient$Stub$Proxy@429dfe58 (uid=10170 pid=7847)

NullPointerException error?

Carmoneer

I think it may be an issue with the signature call on the .cpp side, specifically "(Ljava/lang/String;I)V". Try:

QString toastMessage = "My message";
QAndroidJniObject javaMessage = QAndroidJniObject::fromString(toastMessage);
QAndroidJniObject::callStaticMethod<void>("com/app/myApp/MyJavaMain",
                                          "MyMethodCallToast",
                                          "(Ljava/lang/String;)V",
                                          javaMessage.object<jstring>());

Ibrahim

@Carmoneer Thanks, but I get same error again. This NullPointerException is text.

Ibrahim

I tried:

// ToastMessage.java file
...
public static void makeText(final String text) {
    mInstance.runOnUiThread(new Runnable() {
      public void run() {
        Toast.makeText(mInstance.getApplicationContext(), "text", Toast.LENGTH_LONG).show();
      }
    });
  }
...

This code give error. I put the string ("text") but I get still NullPointerException error.

Carmoneer

The only other thing I can think of is maybe because you have a separate 'Toast' class, it's calling that nullpointerexception. I don't have a separate class for my Toast calls.

Maybe

Toast.makeText(Classname.class, message, Toast.LENGTH_SHORT).show();

is what you need to do?

I simply import android.widget.Toast and make my Toast calls.

Ibrahim

@Carmoneer My ToastMessage.java file:

package com.classes.java;

import org.qtproject.qt5.android.bindings.QtActivity;
import android.widget.Toast;

public class ToastMessage extends QtActivity {
  public static ToastMessage mInstance;

  public ToastMessage() {
    mInstance = this;
  }

  public static String msg() {
    return "<HELLO WORLD!>";
  }

  public static void makeText(final String text) {
    mInstance.runOnUiThread(new Runnable() {
      public void run() {
        Toast.makeText(mInstance.getApplicationContext(), "text", Toast.LENGTH_LONG).show();
      }
    });
  }
}

I want to learn how to call java codes from C++. Have you an example project for the android toast message?

Carmoneer

This is how I extend the framework for QtActivity:

package com.app.myapp;

import org.qtproject.qt5.android.bindings.QtApplication;
import org.qtproject.qt5.android.bindings.QtActivity;


import android.widget.Toast;


/** --------------------------------------------------------------------------
** @MyJavaNatives
** Static methods called from .cpp side. Sends data to .cpp
** -------------------------------------------------------------------------*/
class MyJavaNatives
{
    public static native void showToast(final String message);
}

/** --------------------------------------------------------------------------
** @JavaMain (Only one class can extend QtActivity)
** -------------------------------------------------------------------------*/
public class JavaMain extends QtActivity {
    // Singleton Instance
    public  static JavaMain mInstance;

    public JavaMain() {
        Log.d(QtApplication.QtTAG, "Java constructor called.");
        mInstance = this;
    }

    // Called at the start of the full lifetime.
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(QtApplication.QtTAG, "onCreate Called");
    }


    // Called at the start of the visible lifetime.
    @Override
    protected void onStart() {
        super.onStart();
    }

    // Called at the start of the active lifetime.
    @Override
    public synchronized void onResume() {
        super.onResume();
    }

    // Called at the end of the active lifetime.
    @Override
    protected synchronized void onPause() {
        super.onPause();
    }

    // Called at the end of the full lifetime.
    @Override
    protected void onDestroy() {
        // Clean up any resources including ending threads,
        // closing database connections etc.
        super.onDestroy();
    }

    // Called at the end of the visible lifetime.
    @Override
    protected void onStop() {
        // Suspend remaining UI updates, threads, or processing
        // that aren’t required when the Activity isn’t visible.
        // Persist all edits or state changes
        // as after this call the process is likely to be killed.
        super.onStop();
 
    }

    // Called before subsequent visible lifetimes
    // for an activity process.
    @Override
    protected void onRestart() {
        // Load changes knowing that the activity has already
        // been visible within this process.
        super.onRestart();
    }


    /** ------------------------------------------------------------------------
    ** @Toast
    ** Show toast messge.
    ** -----------------------------------------------------------------------*/
    public static void showToast(final String message) {
        mInstance.runOnUiThread(new Runnable() {
           public void run() {
               Toast.makeText(mInstance.getApplicationContext(),
                              message,
                              Toast.LENGTH_SHORT).show();
           }
        });
    }
}

and then on the .cpp to call the message:

            QAndroidJniObject::callStaticMethod<void>("com/app/myapp/JavaMain",
                                                      "showToast",
                                                      "(Ljava/lang/String;)V",
                                                      QAndroidJniObject::fromString("This is my toast message!").object<jstring>());

That is the basics to setting up a 'Main' java class that extends QtActivity. Hopefully that should at least steer you in the right direction. Good luck :)

Ibrahim

@Carmoneer Ohh thanks. I tried this project, but it give same error:

W/dalvikvm(18212): Exception thrown (Ljava/lang/NullPointerException;) while throwing internal exception (Ljava/lang/NullPointerException;)
I/InputDispatcher(  589): Delivering touch to (18212): action: 0x0, toolType: 1
I/InputDispatcher(  589): Delivering touch to (18212): action: 0x1, toolType: 1

I am sharing this project source codes: Project Source Codes.

douyw

There is an android-extra example called 'notification' in Qt SDK examples. Just change the notify function in NotificationClient.java to display the toast. Maybe it will work.

Ibrahim

@douyw thanks, I tried this method and it is work. Interesting! I do not understand. What is the problem? How can I learn it?