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PONullPointerException on lockCanvas()
 

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  1. PONullPointerException on lockCanvas()
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    <p>I'm developing a little game (test) for Android, but I don't understand the logic to make a good Timer thread with SurfaceView.</p> <p>I'm getting a problem with [SurfaceView object].getHolder().lockCanvas(null). The problem is that lockCanvas is returning an invalid value (null, on this case).</p> <p>I can't catch this exception because I... can't! :/</p> <p>This is my code:</p> <pre><code>package game; import game.logics.SceneGroup; import game.scenes.TeamScene; import java.util.Timer; import java.util.TimerTask; import android.app.Activity; import android.content.Context; import android.graphics.Canvas; import android.graphics.Color; import android.os.Bundle; import android.view.SurfaceHolder; import android.view.SurfaceView; import android.view.Window; import android.view.WindowManager; // Definição da Atividade public class GameActivity extends Activity { // Definição do Ambiente public class GameSurface extends SurfaceView implements SurfaceHolder.Callback { public GameSurface(final Context context) { super(context); this.getHolder().addCallback(this); this.setFocusable(true); } @Override public void surfaceChanged(final SurfaceHolder arg0, final int arg1, final int arg2, final int arg3) {} @Override public void surfaceCreated(final SurfaceHolder arg0) { GameActivity.this.running = true; } @Override public void surfaceDestroyed(final SurfaceHolder arg0) { GameActivity.this.running = false; } public void update(final Canvas canvas) { GameActivity.this.scenes.update(canvas); } } class GameTask extends TimerTask { @Override public void run() { if(GameActivity.this.running == false) { return; } final SurfaceHolder holder = GameActivity.this.surface.getHolder(); Canvas canvas = null; try { canvas = holder.lockCanvas(); canvas.drawColor(Color.BLACK); synchronized(holder) { GameActivity.this.surface.update(canvas); } } finally { if(canvas != null) { holder.unlockCanvasAndPost(canvas); } } } } private GameSurface surface; private SceneGroup scenes; private Timer timer; private TimerTask task; private boolean running = false; @Override public void onCreate(final Bundle savedInstanceState) { super.onCreate(savedInstanceState); this.requestWindowFeature(Window.FEATURE_NO_TITLE); this.getWindow().setFlags( WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN); // ### SOLVE: PROBLEM START HERE ### this.surface = new GameSurface(this); this.scenes = new SceneGroup(this); this.scenes.add(new TeamScene(this)); this.timer = new Timer(); this.task = new GameTask(); // ### SOLVE: PROBLEM END HERE ### // ### Invalid new instance of GameSurface ### this.setContentView(new GameSurface(this)); } @Override public void onPause() { super.onPause(); this.timer.cancel(); } @Override public void onResume() { super.onResume(); this.timer.scheduleAtFixedRate(this.task, 0, 33); } } </code></pre> <p>I'm doing right? What I can do to fix my code?</p>
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    1. USDavid Rodrigues
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    1. COI suspect your problem is that you're calling surface.getHolder(), from a non-guid thread. Save the holder in your onCreate method, and then access it to lockCanvas, as you are doing and see if that helps.
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    2. COThanks. But I have tried, like that `this.surface = new GameSurface(this); /* then */ this.holder = this.surface.getHolder();` but too don't works. More one suspect for my problem?
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      1. USDavid Rodrigues
    3. COUmm... You know you're creating the GameSurface twice? One you're assigning to this.surface, the second your passing to setContentView... presumably they should be the same one?!?
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      1. USforsvarir
 

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