Android: Unfortunately, App has stopped

Question

The app is used as a countdown with a start and stop button. But I don´t know what is wrong...

I use Android Studio 1.5.1 with it's emulator or my smartphone but on both the same failure occur.

Here is my main activity:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    tools:context="letscho.timer.MainActivity">


    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/btnStart"
        android:layout_alignParentLeft="true"
        android:layout_centerVertical="true"
        android:layout_marginLeft="28dp"
        android:text="Start"/>

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/btnStop"
        android:layout_alignParentRight="true"
        android:layout_centerVertical="true"
        android:layout_marginRight="67dp"
        android:text="Stop"/>


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/textViewTime"
        android:layout_above="@+id/btnStart"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="17dp"
        android:textSize="25sp"/>
</RelativeLayout>

And my MainActivity:

package letscho.timer;

import android.annotation.SuppressLint;
import android.annotation.TargetApi;
import android.os.Build;
import android.os.CountDownTimer;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.util.concurrent.TimeUnit;


@TargetApi(Build.VERSION_CODES.GINGERBREAD)
@SuppressLint("NewApi")
public class MainActivity extends AppCompatActivity {

    Button btnStart, btnStop;
    TextView textViewTime;

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

        btnStart = (Button) findViewById(R.id.btnStart);
        btnStart = (Button) findViewById(R.id.btnStop);
        textViewTime = (TextView) findViewById(R.id.textViewTime);

        textViewTime.setText("00:03:00");

        final CounterClass timer = new CounterClass(18000, 1000);
        btnStart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                timer.start();
            }
        });

        btnStop.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                timer.cancel();
            }
        });

    }

    @TargetApi(Build.VERSION_CODES.GINGERBREAD)
    @SuppressLint("NewApi")
    public class CounterClass extends CountDownTimer {
        /**
         * @param millisInFuture    The number of millis in the future from the call
         *                          to {@link #start()} until the countdown is done and {@link #onFinish()}
         *                          is called.
         * @param countDownInterval The interval along the way to receive
         *                          {@link #onTick(long)} callbacks.
         */
        public CounterClass(long millisInFuture, long countDownInterval) {
            super(millisInFuture, countDownInterval);
        }

        @SuppressLint("NewApi")
        @TargetApi(Build.VERSION_CODES.GINGERBREAD)
        @Override
        public void onTick(long millisUntilFinished) {

            long millis = millisUntilFinished;
            String hms = String.format("%02d:%02d:%02d", TimeUnit.MILLISECONDS.toHours(millis),
                    TimeUnit.MILLISECONDS.toMinutes(millis) - TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(millis)),
                    TimeUnit.MILLISECONDS.toSeconds(millis) - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis)));
            System.out.println(hms);
            textViewTime.setText(hms);

        }

        @Override
        public void onFinish() {
            textViewTime.setText("00:00:00");

        }
    }

}

https://stackoverflow.com/questions/23353173/unfortunately-myapp-has-stopped-how-can-i-solve-this — CommonsWare, Dec 12 '15 at 20:00

score 4 · Answer 1 · answered Dec 12 '15 at 20:06

well your problem is

    btnStart = (Button) findViewById(R.id.btnStart);
    btnStart = (Button) findViewById(R.id.btnStop);

both of them reference the same location then you set ClickListener on a Null refrenece.

  btnStop.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            timer.cancel();
        }
    });

btnStop is Null.

Android: Unfortunately, App has stopped

1 Answers1