【发布时间】：2011-03-22 22:36:28
【问题描述】：
大家好！我在女巫中有这个动态壁纸，我尝试通过画布显示位图（可绘制资源是 400k 1900x1200 jpg）。它强制关闭，我不明白为什么（这是我的第一个 Android 项目）。这些是“重要”位：
wallEngine() { // CONSTRUCTOR <<<<<<<<<<<<<<<<<<<
mStartTime = SystemClock.elapsedRealtime();
Log.v(Logcat, "Contructor ok");
}
//====================================== INIT
private final Runnable mDrawWall = new Runnable() { //=========== RUN
public void run() {
drawFrame();
}
};
void drawFrame() {
final SurfaceHolder holder = getSurfaceHolder();
Canvas c = null;
try {
c = holder.lockCanvas();
if (c != null) {
// draw something
updatePhysics();
doDraw(c);
}
} finally {
if (c != null) holder.unlockCanvasAndPost(c);
}
// Reschedule the next redraw
mHandler.removeCallbacks(mDrawWall);
if (mVisible) {
mHandler.postDelayed(mDrawWall, 5000);
}
}
private void doDraw(Canvas canvas) {
//backgroundImage.prepareToDraw();
canvas.drawBitmap(this.backgroundImage, 0, 0, null);
}
public void onCreate(SurfaceHolder surfaceHolder) {
super.onCreate(surfaceHolder); surfaceHolder.setFormat(android.graphics.PixelFormat.RGBA_8888);
BitmapFactory.Options options = new BitmapFactory.Options();
options.inPurgeable = true;
this.backgroundImage = BitmapFactory.decodeResource(getResources(),
com.misca.livewallpapers.parang.R.drawable.a, options);
//backgroundImage.prepareToDraw();
//setTouchEventsEnabled(true);
Log.v(Logcat, "onCreate ok");
}
当我尝试在手机上运行它时出现的 logcat 错误是：
ERROR/AndroidRuntime(7722): FATAL EXCEPTION: main
ERROR/AndroidRuntime(7722): java.lang.NullPointerException
ERROR/AndroidRuntime(7722): at android.graphics.Canvas.throwIfRecycled(Canvas.java:957)
ERROR/AndroidRuntime(7722): at android.graphics.Canvas.drawBitmap(Canvas.java:983)
ERROR/AndroidRuntime(7722): at com.misca.livewallpapers.parang.liveWallpaper$wallEngine.doDraw(liveWallpaper.java:115)
ERROR/AndroidRuntime(7722): at com.misca.livewallpapers.parang.liveWallpaper$wallEngine.drawFrame(liveWallpaper.java:75)
ERROR/AndroidRuntime(7722): at com.misca.livewallpapers.parang.liveWallpaper$wallEngine.onSurfaceChanged(liveWallpaper.java:157)
ERROR/AndroidRuntime(7722): at android.service.wallpaper.WallpaperService$Engine.updateSurface(WallpaperService.java:590)
ERROR/AndroidRuntime(7722): at android.service.wallpaper.WallpaperService$Engine.attach(WallpaperService.java:654)
ERROR/AndroidRuntime(7722): at android.service.wallpaper.WallpaperService$IWallpaperEngineWrapper.executeMessage(WallpaperService.java:878)
ERROR/AndroidRuntime(7722): at com.android.internal.os.HandlerCaller$MyHandler.handleMessage(HandlerCaller.java:61)
ERROR/AndroidRuntime(7722): at android.os.Handler.dispatchMessage(Handler.java:99)
ERROR/AndroidRuntime(7722): at android.os.Looper.loop(Looper.java:123)
ERROR/AndroidRuntime(7722): at android.app.ActivityThread.main(ActivityThread.java:3848)
ERROR/AndroidRuntime(7722): at java.lang.reflect.Method.invokeNative(Native Method)
ERROR/AndroidRuntime(7722): at java.lang.reflect.Method.invoke(Method.java:507)
ERROR/AndroidRuntime(7722): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
ERROR/AndroidRuntime(7722): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
03-23 00:26:42.309: ERROR/AndroidRuntime(7722): at dalvik.system.NativeStart.main(Native Method)
谢谢！ :)
======================== 新闻：
private void doDraw(Canvas canvas) {
//backgroundImage.prepareToDraw();
if(this.backgroundImage!=null)
canvas.drawBitmap(this.backgroundImage, 0, 0, null);
else
Log.v(Logcat, "null");
}
而且似乎位图为空。现在我正在使用 480x800 以确保没有内存问题。应用程序不再因 if 语句而崩溃（黑屏）
【问题讨论】：
-
在onCreate过程中实例化的backgroundImage成员是否保证不为空？如果是这样，似乎图像正在被回收，因此图像引用无效，因此出现 NullPointerException。
-
你是对的！它是空的，谢谢。有没有更好的方式将其加载到位图中？