Android：简单的线程示例崩溃

Question

I'm trying to find out how does the working thread in Android Studio work. I created a simple example but I'm struggling with following issues, the java code is:

package tlacitko.button;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

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

    public void sendMessage(View view) {
        new Thread(new Runnable() {
            public void run() {
                Toast.makeText(getBaseContext(), "Your answer is correct!" , Toast.LENGTH_SHORT ).show();
            }
        }).start();

    }

}

and the xml code is:

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="7dp"
        android:layout_marginTop="16dp"
        android:onClick="sendMessage"
        android:text="Ahoj"
        app:layout_constraintLeft_toRightOf="@+id/editText"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />


</android.support.constraint.ConstraintLayout>

The code is build ok but after button click the app crashes with following error:

Button has stopped.

Answer 1

you need to use handler to work with UI components. You can use runOnUiThread(runnable)

public class MainActivity extends AppCompatActivity {

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

        public void sendMessage(View view) {   
            runOnUiThread(new Runnable() {
               @Override
               public void run()
               {
                  Toast.makeText(getBaseContext(), "Your answer is correct!" , Toast.LENGTH_SHORT ).show();
               }
            });
        }

    }

Answer 2

You can't do UI work from non UI thread. Try to wrap it like this:

runOnUiThread(new Runnable() {
    @Override
    public void run() {
       Toast.makeText(getBaseContext(), "Your answer is correct!" , Toast.LENGTH_SHORT ).show();
    }
});

But think again is it good and can you write more elegant solution for it.