Tentative d'invoquer une méthode virtuelle

Question

J'essaie de créer un minuteur simple en utilisant les classes Timer et TimerTask. Je reçois toujours l'erreur suivante:

Caused by: Java.lang.NullPointerException: Attempt to invoke virtual method 'Android.view.View Android.view.Window.findViewById(int)' on a null object reference

Voici mon code:

package com.austinheitmann.stopwatch;

import Android.os.CountDownTimer;
import Android.os.SystemClock;
import Android.support.v7.app.ActionBarActivity;
import Android.os.Bundle;
import Android.util.Log;
import Android.view.Menu;
import Android.view.MenuItem;
import Android.view.View;
import Android.widget.TextView;

import Java.util.Timer;
import Java.util.TimerTask;


public class MainActivity extends ActionBarActivity {

TextView timerf;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
timerf = (TextView) findViewById(R.id.timer);
}

int i=0;




TimerTask time = new TimerTask() {
    public void run() {
        i++;
        int k = i/60;
        int j = i%60;
        if (j>9) {
            timerf.setText("seconds remaining: " + k + ":" + j);
        }else {
            timerf.setText("seconds remaining: " + k + ":0" + j);
        }
        Log.d("Uhh", "Sec:" + i);
    }
};

Timer timers = new Timer();

public void startB(View view) {
timers.schedule(time, 100000000, 1000);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;

}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}
}
}

Voici le fichier xml (layout):

<RelativeLayout xmlns:Android="http://schemas.Android.com/apk/res/Android"
xmlns:tools="http://schemas.Android.com/tools"            Android:layout_width="match_parent"
Android:layout_height="match_parent"   Android:paddingLeft="@dimen/activity_horizontal_margin"
Android:paddingRight="@dimen/activity_horizontal_margin"
Android:paddingTop="@dimen/activity_vertical_margin"
Android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

<TextView
    Android:layout_width="wrap_content"
    Android:layout_height="wrap_content"
    Android:textAppearance="?android:attr/textAppearanceLarge"
    Android:text="0:00"
    Android:id="@+id/timer"
    Android:layout_alignParentTop="true"
    Android:layout_centerHorizontal="true"
    Android:layout_marginTop="54dp" />

<Button
    Android:layout_width="wrap_content"
    Android:layout_height="wrap_content"
    Android:text="Start/Pause"
    Android:id="@+id/start"
    Android:layout_below="@+id/timer"
    Android:layout_alignParentLeft="true"
    Android:layout_alignParentStart="true"
    Android:layout_marginTop="119dp"
    Android:onClick="startB"/>

<Button
    Android:layout_width="wrap_content"
    Android:layout_height="wrap_content"
    Android:text="Stop/Reset"
    Android:id="@+id/stop"
    Android:layout_alignBottom="@+id/start"
    Android:layout_alignParentRight="true"
    Android:layout_alignParentEnd="true" />
</RelativeLayout>

Chaque solution que j'ai vue à cette erreur a à voir avec la mise en page, mais je ne modifie pas cela de toute façon. J'ai également déplacé vers le TimerTask dans la classe startB et j'obtiens la même erreur. Comment puis-je corriger cette erreur?

Voici l'erreur complète que j'obtiens d'une exécution après avoir effacé le logcat (je mets ** là où l'erreur se produit):

01-16 12:27:21.008    2455-2455/com.austinheitmann.stopwatch I/art﹕ Not late-enabling -Xcheck:jni (already on)
01-16 12:27:21.119    2455-2455/com.austinheitmann.stopwatch D/AndroidRuntime﹕ Shutting down VM
    --------- beginning of crash
01-16 12:27:21.123    2455-2455/com.austinheitmann.stopwatch E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.austinheitmann.stopwatch, PID: 2455
    Java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.austinheitmann.stopwatch/com.austinheitmann.stopwatch.MainActivity}: Java.lang.NullPointerException: Attempt to invoke virtual method 'Android.view.View Android.view.Window.findViewById(int)' on a null object reference
            at Android.app.ActivityThread.performLaunchActivity(ActivityThread.Java:2209)
            at Android.app.ActivityThread.handleLaunchActivity(ActivityThread.Java:2360)
            at Android.app.ActivityThread.access$800(ActivityThread.Java:144)
            at Android.app.ActivityThread$H.handleMessage(ActivityThread.Java:1278)
            at Android.os.Handler.dispatchMessage(Handler.Java:102)
            at Android.os.Looper.loop(Looper.Java:135)
            at Android.app.ActivityThread.main(ActivityThread.Java:5221)
            at Java.lang.reflect.Method.invoke(Native Method)
            at Java.lang.reflect.Method.invoke(Method.Java:372)
            at com.Android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.Java:899)
            at com.Android.internal.os.ZygoteInit.main(ZygoteInit.Java:694)
     Caused by: Java.lang.NullPointerException: Attempt to invoke virtual method 'Android.view.View Android.view.Window.findViewById(int)' on a null object reference
            at Android.app.Activity.findViewById(Activity.Java:2071)
            at com.austinheitmann.stopwatch.MainActivity.<init>(MainActivity.Java:25)
            at Java.lang.reflect.Constructor.newInstance(Native Method)
            at Java.lang.Class.newInstance(Class.Java:1572)
            at Android.app.Instrumentation.newActivity(Instrumentation.Java:1065)
            at Android.app.ActivityThread.performLaunchActivity(ActivityThread.Java:2199)
            at Android.app.ActivityThread.handleLaunchActivity(ActivityThread.Java:2360)
            at Android.app.ActivityThread.access$800(ActivityThread.Java:144)
            at Android.app.ActivityThread$H.handleMessage(ActivityThread.Java:1278)
            at Android.os.Handler.dispatchMessage(Handler.Java:102)
            at Android.os.Looper.loop(Looper.Java:135)
            at Android.app.ActivityThread.main(ActivityThread.Java:5221)
            at Java.lang.reflect.Method.invoke(Native Method)
            at Java.lang.reflect.Method.invoke(Method.Java:372)
            at com.Android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.Java:899)
            at com.Android.internal.os.ZygoteInit.main(ZygoteInit.Java:694)
01-16 12:44:57.778    2582-2582/com.austinheitmann.stopwatch D/AndroidRuntime﹕ Shutting down VM
01-16 12:44:57.778    2582-2582/com.austinheitmann.stopwatch E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.austinheitmann.stopwatch, PID: 2582
    Java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.austinheitmann.stopwatch/com.austinheitmann.stopwatch.MainActivity}: Java.lang.NullPointerException: Attempt to invoke virtual method 'Android.view.View Android.view.Window.findViewById(int)' on a null object reference
            at Android.app.ActivityThread.performLaunchActivity(ActivityThread.Java:2209)
            at Android.app.ActivityThread.handleLaunchActivity(ActivityThread.Java:2360)
            at Android.app.ActivityThread.access$800(ActivityThread.Java:144)
            at Android.app.ActivityThread$H.handleMessage(ActivityThread.Java:1278)
            at Android.os.Handler.dispatchMessage(Handler.Java:102)
            at Android.os.Looper.loop(Looper.Java:135)
            at Android.app.ActivityThread.main(ActivityThread.Java:5221)
            at Java.lang.reflect.Method.invoke(Native Method)
            at Java.lang.reflect.Method.invoke(Method.Java:372)
            at com.Android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.Java:899)
            at com.Android.internal.os.ZygoteInit.main(ZygoteInit.Java:694)
     Caused by: Java.lang.NullPointerException: Attempt to invoke virtual method 'Android.view.View Android.view.Window.findViewById(int)' on a null object reference
            at Android.app.Activity.findViewById(Activity.Java:2071)
            at com.austinheitmann.stopwatch.MainActivity.<init>(MainActivity.Java:25)
            at Java.lang.reflect.Constructor.newInstance(Native Method)
            at Java.lang.Class.newInstance(Class.Java:1572)
            at Android.app.Instrumentation.newActivity(Instrumentation.Java:1065)
            at Android.app.ActivityThread.performLaunchActivity(ActivityThread.Java:2199)
            at Android.app.ActivityThread.handleLaunchActivity(ActivityThread.Java:2360)
            at Android.app.ActivityThread.access$800(ActivityThread.Java:144)
            at Android.app.ActivityThread$H.handleMessage(ActivityThread.Java:1278)
            at Android.os.Handler.dispatchMessage(Handler.Java:102)
            at Android.os.Looper.loop(Looper.Java:135)
            at Android.app.ActivityThread.main(ActivityThread.Java:5221)
            at Java.lang.reflect.Method.invoke(Native Method)
            at Java.lang.reflect.Method.invoke(Method.Java:372)
            at com.Android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.Java:899)
            at com.Android.internal.os.ZygoteInit.main(ZygoteInit.Java:694)
01-16 12:46:25.059    2641-2641/com.austinheitmann.stopwatch D/AndroidRuntime﹕ Shutting down VM
01-16 12:46:25.059    2641-2641/com.austinheitmann.stopwatch E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.austinheitmann.stopwatch, PID: 2641
    Java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.austinheitmann.stopwatch/com.austinheitmann.stopwatch.MainActivity}: Java.lang.NullPointerException: Attempt to invoke virtual method 'Android.view.View Android.view.Window.findViewById(int)' on a null object reference
            at Android.app.ActivityThread.performLaunchActivity(ActivityThread.Java:2209)
            at Android.app.ActivityThread.handleLaunchActivity(ActivityThread.Java:2360)
            at Android.app.ActivityThread.access$800(ActivityThread.Java:144)
            at Android.app.ActivityThread$H.handleMessage(ActivityThread.Java:1278)
            at Android.os.Handler.dispatchMessage(Handler.Java:102)
            at Android.os.Looper.loop(Looper.Java:135)
            at Android.app.ActivityThread.main(ActivityThread.Java:5221)
            at Java.lang.reflect.Method.invoke(Native Method)
            at Java.lang.reflect.Method.invoke(Method.Java:372)
            at com.Android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.Java:899)
            at com.Android.internal.os.ZygoteInit.main(ZygoteInit.Java:694)
     Caused by: Java.lang.NullPointerException: Attempt to invoke virtual method 'Android.view.View Android.view.Window.findViewById(int)' on a null object reference
            at Android.app.Activity.findViewById(Activity.Java:2071)
            at com.austinheitmann.stopwatch.MainActivity.<init>(MainActivity.Java:25)
            at Java.lang.reflect.Constructor.newInstance(Native Method)
            at Java.lang.Class.newInstance(Class.Java:1572)
            at Android.app.Instrumentation.newActivity(Instrumentation.Java:1065)
            at Android.app.ActivityThread.performLaunchActivity(ActivityThread.Java:2199)
            at Android.app.ActivityThread.handleLaunchActivity(ActivityThread.Java:2360)
            at Android.app.ActivityThread.access$800(ActivityThread.Java:144)
            at Android.app.ActivityThread$H.handleMessage(ActivityThread.Java:1278)
            at Android.os.Handler.dispatchMessage(Handler.Java:102)
            at Android.os.Looper.loop(Looper.Java:135)
            at Android.app.ActivityThread.main(ActivityThread.Java:5221)
            at Java.lang.reflect.Method.invoke(Native Method)
            at Java.lang.reflect.Method.invoke(Method.Java:372)
            at com.Android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.Java:899)
            at com.Android.internal.os.ZygoteInit.main(ZygoteInit.Java:694)
01-16 12:47:50.630    2702-2702/com.austinheitmann.stopwatch D/AndroidRuntime﹕ Shutting down VM
01-16 12:47:50.630    2702-2702/com.austinheitmann.stopwatch E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.austinheitmann.stopwatch, PID: 2702
    Java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.austinheitmann.stopwatch/com.austinheitmann.stopwatch.MainActivity}: Java.lang.NullPointerException: Attempt to invoke virtual method 'Android.view.View Android.view.Window.findViewById(int)' on a null object reference
            at Android.app.ActivityThread.performLaunchActivity(ActivityThread.Java:2209)
            at Android.app.ActivityThread.handleLaunchActivity(ActivityThread.Java:2360)
            at Android.app.ActivityThread.access$800(ActivityThread.Java:144)
            at Android.app.ActivityThread$H.handleMessage(ActivityThread.Java:1278)
            at Android.os.Handler.dispatchMessage(Handler.Java:102)
            at Android.os.Looper.loop(Looper.Java:135)
            at Android.app.ActivityThread.main(ActivityThread.Java:5221)
            at Java.lang.reflect.Method.invoke(Native Method)
            at Java.lang.reflect.Method.invoke(Method.Java:372)
            at com.Android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.Java:899)
            at com.Android.internal.os.ZygoteInit.main(ZygoteInit.Java:694)
     **Caused by: Java.lang.NullPointerException: Attempt to invoke virtual method 'Android.view.View Android.view.Window.findViewById(int)' on a null object reference**
            at Android.app.Activity.findViewById(Activity.Java:2071)
            at com.austinheitmann.stopwatch.MainActivity.<init>(MainActivity.Java:25)
            at Java.lang.reflect.Constructor.newInstance(Native Method)
            at Java.lang.Class.newInstance(Class.Java:1572)
            at Android.app.Instrumentation.newActivity(Instrumentation.Java:1065)
            at Android.app.ActivityThread.performLaunchActivity(ActivityThread.Java:2199)
            at Android.app.ActivityThread.handleLaunchActivity(ActivityThread.Java:2360)
            at Android.app.ActivityThread.access$800(ActivityThread.Java:144)
            at     Android.app.ActivityThread$H.handleMessage(ActivityThread.Java:1278)
            at Android.os.Handler.dispatchMessage(Handler.Java:102)
            at Android.os.Looper.loop(Looper.Java:135)
            at Android.app.ActivityThread.main(ActivityThread.Java:5221)
            at Java.lang.reflect.Method.invoke(Native Method)
            at Java.lang.reflect.Method.invoke(Method.Java:372)
            at      com.Android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.Java:899)
            at com.Android.internal.os.ZygoteInit.main(ZygoteInit.Java:694)

Answer 1

Vous essayez de findViewById avant que le contexte de l'activité ne soit prêt.

Si vous souhaitez également accéder à timerf dans d'autres méthodes, créez un membre de classe mais effectuez l'initialisation dans onCreate après setContentView:

TextView timerf;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    timerf = (TextView) findViewById(R.id.timer);
}

Mise à jour:

Je n'ai pas remarqué les autres variables de membre de classe que vous instanciez. Ils font référence à timerf qui est nul.

Vous devez également les initialiser dans le onCreate. Voici le code complet qui devrait fonctionner:

package com.austinheitmann.stopwatch;

import Android.os.CountDownTimer;
import Android.os.SystemClock;
import Android.support.v7.app.ActionBarActivity;
import Android.os.Bundle;
import Android.util.Log;
import Android.view.Menu;
import Android.view.MenuItem;
import Android.view.View;
import Android.widget.TextView;

import Java.util.Timer;
import Java.util.TimerTask;


public class MainActivity extends ActionBarActivity {

    Timer timers = new Timer();
    TextView timerf;
    TimerTask time;
    int i=0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        timerf = (TextView) findViewById(R.id.timer);

        time = new TimerTask() {
            public void run() {
                i++;
                int k = i/60;
                int j = i%60;
                if (j>9) {
                    timerf.setText("seconds remaining: " + k + ":" + j);
                }else {
                    timerf.setText("seconds remaining: " + k + ":0" + j);
                }
                Log.d("Uhh", "Sec:" + i);
            }
        };
    }

    public void startB(View view) {
        timers.schedule(time, 100000000, 1000);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;

    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}