Android GC注意事項 - GC何時運行，並且可以從代碼跟蹤其運行狀態？

我一直在尋找一些時間來描述Dalvik虛擬機的垃圾收集器的體系結構的詳細設計文檔，但沒有太多發現。鑑於GC運行的性能影響，我真的想更好地理解5個具體問題： 1.究竟是什麼觸發了Android中的GC？我見過的其他VM實現通常允許在GC接收到運行信號之前將一定百分比的系統內存分配給應用程序。掃描以下logcat的但是似乎表明Dalvik的GC運行至少部分相當下意識的Android GC注意事項 - GC何時運行，並且可以從代碼跟蹤其運行狀態？

12-14 11:34:57.753: D/dalvikvm(279): GC_EXTERNAL_ALLOC freed 735 objects/54272 bytes 
in 90ms 
12-14 11:34:57.893: D/dalvikvm(279): GC_EXTERNAL_ALLOC freed 256 objects/12240 bytes 
in 61ms 
12-14 11:34:57.943: I/jPCT-AE(279): Loading Texture... 
12-14 11:34:57.993: D/dalvikvm(279): GC_FOR_MALLOC freed 65 objects/2840 bytes in 
52ms 
12-14 11:34:58.013: I/dalvikvm-heap(279): Grow heap (frag case) to 5.039MB for 
1048592-byte allocation 
12-14 11:34:58.073: D/dalvikvm(279): GC_FOR_MALLOC freed 1 objects/40 bytes in 59ms 
12-14 11:34:58.243: D/dalvikvm(279): GC_EXTERNAL_ALLOC freed 11 objects/432 bytes in 
55ms 
12-14 11:34:58.283: I/jPCT-AE(279): Loading Texture... 
12-14 11:34:58.333: D/dalvikvm(279): GC_FOR_MALLOC freed 10 objects/416 bytes in 46ms 
12-14 11:34:58.344: I/dalvikvm-heap(279): Grow heap (frag case) to 6.040MB for 
1048592-byte allocation 
12-14 11:34:58.423: D/dalvikvm(279): GC_FOR_MALLOC freed 2 objects/80 bytes in 75ms 
12-14 11:34:58.563: D/dalvikvm(279): GC_EXTERNAL_ALLOC freed 10 objects/384 bytes in 
47ms 
12-14 11:34:58.603: I/jPCT-AE(279): Loading Texture... 
12-14 11:34:58.653: D/dalvikvm(279): GC_FOR_MALLOC freed 11 objects/464 bytes in 44ms 
12-14 11:34:58.663: I/dalvikvm-heap(279): Grow heap (frag case) to 7.040MB for 
1048592-byte allocation 
12-14 11:34:58.743: D/dalvikvm(279): GC_FOR_MALLOC freed 2 objects/80 bytes in 75ms 
12-14 11:34:58.973: I/System.out(279): started document! 
... 
12-14 11:43:05.393: I/jPCT-AE(279): Memory usage before compacting: 5867 KB used out 
of 6215 KB 
12-14 11:43:05.453: D/dalvikvm(279): GC_EXPLICIT freed 2560 objects/145712 bytes in 
61ms 
12-14 11:43:05.503: D/dalvikvm(279): GC_EXPLICIT freed 295 objects/21448 bytes in 
51ms 
12-14 11:43:05.717: I/jPCT-AE(279): Memory usage after compacting: 5705 KB used out of 
6215 KB 
... 
12-14 11:43:05.792: D/dalvikvm(279): GC_EXTERNAL_ALLOC freed 105 objects/6152 bytes 
in 56ms 
12-14 11:43:05.855: D/dalvikvm(279): GC_FOR_MALLOC freed 3 objects/80 bytes in 51ms 
... 
12-14 11:43:12.863: D/dalvikvm(279): GC_EXTERNAL_ALLOC freed 864 objects/1099072 
bytes in 70ms 
12-14 11:43:13.053: D/dalvikvm(279): GC_EXTERNAL_ALLOC freed 45 objects/1760 bytes 
in 55ms 
12-14 11:43:14.533: D/dalvikvm(279): GC_EXTERNAL_ALLOC freed 49 objects/2376 bytes 
in 58ms 
12-14 11:43:14.933: D/dalvikvm(279): GC_EXTERNAL_ALLOC freed 34 objects/1408 bytes 
in 55ms 
12-14 11:43:15.423: D/dalvikvm(279): GC_EXTERNAL_ALLOC freed 13 objects/504 bytes in 
58ms 
12-14 11:43:15.953: D/dalvikvm(279): GC_EXTERNAL_ALLOC freed 13 objects/520 bytes in 
56ms 
... 
12-14 11:43:31.203: I/jPCT-AE(279): Visibility lists disposed! 
12-14 11:43:31.203: I/jPCT-AE(279): All texture data unloaded from gpu! 
12-14 11:43:31.203: I/jPCT-AE(279): Renderer disposed! 
12-14 11:43:31.203: I/jPCT-AE(279): Static references cleared... 
... 
12-14 11:43:36.943: E/dalvikvm-heap(279): 2964320-byte external allocation too large 
for this process. 
12-14 11:43:36.953: E/GraphicsJNI(279): VM won't let us allocate 2964320 bytes 
12-14 11:43:36.953: D/AndroidRuntime(279): Shutting down VM 
12-14 11:43:36.953: W/dalvikvm(279): threadid=1: thread exiting with uncaught 
exception (group=0x4001d800) 
12-14 11:43:36.973: E/AndroidRuntime(279): FATAL EXCEPTION: main 
12-14 11:43:36.973: E/AndroidRuntime(279): android.view.InflateException: Binary XML 
file line #33: Error inflating class <unknown> 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.view.LayoutInflater.createView(LayoutInflater.java:513) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
com.android.internal.policy.impl.PhoneLayoutInflater. 
onCreateView(PhoneLayoutInflater.java:56) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:563) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.view.LayoutInflater.rInflate(LayoutInflater.java:618) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.view.LayoutInflater.rInflate(LayoutInflater.java:621) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.view.LayoutInflater.inflate(LayoutInflater.java:407) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.view.LayoutInflater.inflate(LayoutInflater.java:320) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
com.ai.ultimap.views.Manual.onItemClick(Manual.java:467) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.widget.AdapterView.performItemClick(AdapterView.java:284) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.widget.AbsListView$PerformClick.run(AbsListView.java:1696) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.os.Handler.handleCallback(Handler.java:587) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.os.Handler.dispatchMessage(Handler.java:92) 
12-14 11:43:36.973: E/AndroidRuntime(279): at android.os.Looper.loop(Looper.java:123) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.app.ActivityThread.main(ActivityThread.java:4627) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
java.lang.reflect.Method.invokeNative(Native Method) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
java.lang.reflect.Method.invoke(Method.java:521) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
12-14 11:43:36.973: E/AndroidRuntime(279): at dalvik.system.NativeStart.main(Native 
Method) 
12-14 11:43:36.973: E/AndroidRuntime(279): Caused by: 
java.lang.reflect.InvocationTargetException 
12-14 11:43:36.973: E/AndroidRuntime(279): at android.widget.ImageView.<init> 
(ImageView.java:108) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
java.lang.reflect.Constructor.constructNative(Native Method) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
java.lang.reflect.Constructor.newInstance(Constructor.java:446) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.view.LayoutInflater.createView(LayoutInflater.java:500) 
12-14 11:43:36.973: E/AndroidRuntime(279): ... 18 more 
12-14 11:43:36.973: E/AndroidRuntime(279): Caused by: java.lang.OutOfMemoryError: 
bitmap size exceeds VM budget 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.graphics.Bitmap.nativeCreate(Native Method) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.graphics.Bitmap.createBitmap(Bitmap.java:468) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.graphics.Bitmap.createBitmap(Bitmap.java:435) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.graphics.Bitmap.createScaledBitmap(Bitmap.java:340) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.graphics.BitmapFactory.finishDecode(BitmapFactory.java:488) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.graphics.BitmapFactory.decodeStream(BitmapFactory.java:462) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.graphics.BitmapFactory.decodeResourceStream(BitmapFactory.java:323) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.graphics.drawable.Drawable.createFromResourceStream(Drawable.java:697) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.content.res.Resources.loadDrawable(Resources.java:1709) 
12-14 11:43:36.973: E/AndroidRuntime(279): at 
android.content.res.TypedArray.getDrawable(TypedArray.java:601) 
12-14 11:43:36.973: E/AndroidRuntime(279): at android.widget.ImageView.<init> 
(ImageView.java:118) 
12-14 11:43:36.973: E/AndroidRuntime(279): ... 22 more 
12-14 11:43:38.763: I/Process(279): Sending signal. PID: 279 SIG: 9

正如你可以看到我的〜3 MB位圖加載過程中正在運行專門爲內存不足錯誤......這對我來說沒有任何意義，因爲GC最近運行並沒有分配任何內容，因爲它應該將虛擬機的容量限制在3MB以內（256 MB）。是否只有一小部分的256 MB系統RAM在崩潰之前實際提供給VM？難道是位圖加載過程有自己的內存分配上限？我知道對象池是在遊戲循環中嘗試避免GC的一種好方法，但不知道是什麼觸發了Dalvik GC，我們仍然對操作系統和Google對性能最佳實踐的模糊討論抱有極大的信心。

能否GC狀態（例如「即將運行」，「運行」，「運行完畢」）從代碼追蹤，以便大資源分配可能會策略性地周圍可用的計劃記憶？我已閱讀這篇文章：Determine when the Android GC runs它提供了一個有趣的潛在解決方案，但仍然依賴於一個'技巧'。我想知道是否有支持的API調用可以依賴生產代碼（不僅僅是調試）來跟蹤垃圾收集器的準確狀態。 System.gc（）在某些情況下可能會有用如果可以檢查GC狀態;否則，由於它不能保證立即執行GC，所以它的有用性會下降很多。

GC始終是系統範圍的，還是可以將線程分開（例如遊戲的專用渲染線程）以避免由GC引起的潛在性能滯後問題？

鑑於以下假設的情況：「我有一個對象花費（VM RAM預算）/ 2字節來實例化，並且我與單個參考立即實例化。然後，我刪除了該引用，使該對象符合GC的條件，但當然不會實際釋放其內存。然後我立即再次實例化對象。' 這會導致虛擬機崩潰，還是有某種方法可以自動處理這種極端情況，以避免虛擬機崩潰？如果操作系統沒有處理它，我會舉這個爲例，說明爲什麼我上面的問題＃2是有效的;如果可以跟蹤GC狀態，那麼通過檢查GC資格對象的內存是否在加載之前已被釋放，可以在源中包含邏輯以處理巨大的對象分配問題（實際上可能比設計錯誤的類更大的資源）新的巨大對象實例，並在背景中輪詢GC時顯示一個小的加載動畫。這應該避免應用程序沒有響應錯誤以及合法的內存不足錯誤......某種onGC（）偵聽器將是理想的; GC偵聽器是否可以用本機代碼實現而不需要重新構建操作系統內核？

5.最後，一些源代碼...我是否有正確的想法來實現高性能的Android編程？

活動課：

package com.ai.ultimap; 

//imports omitted... 

public class UltiMapActivity extends Activity { 
//Housekeeping 
private String viewDriverID = ""; 
private static final int TUTORIAL = 7; 

//visuals 
private HomeView hv; //home view 
private ConfigView cv; //config view 
private MapView mv; //map view 
private Manual man; //manual view 
private int manCount = 0; //tracks the number of times the manual has been called 
    //with menu button, ignoring button presses unless value is zero 
private PathCreator pcv; //path creator view 
private MasterGL mgl; //the gl center 
private String pending = "Coming soon..."; 
private PathCreator draw; 
private Surfacer morlock; 
// Used to handle pause and resume... 
private static UltiMapActivity master; 

//XML I/O considerations 
private String fXML = "mypaths.xml"; 
private String sXML = "data was not saved properly...?"; 
private FileOutputStream fos; 
private FileInputStream fis; 
private FileWriter fw; 
private FileReader fr; 
private Date theDate = new Date(); 
private char[] buf = new char[1]; 

//Feedback stuffs 
private FeedbackController feed; 

//tracking you... :) 
private WifiStalk stalk; 
private long lat; 
private long longitude; 

//Testing 
private DrawView dv; 

/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    Log.d("me","ultimap created!"); 
    master = null; 
    mgl = new MasterGL(this); //revisit this later for versatility 
    man = new Manual(this); 
    feed = new FeedbackController(this); 
    stalk = new WifiStalk(this); 
    draw = new PathCreator(this); 
    hv = new HomeView(this,draw); 
    try { 
     BeanCounter bean = new BeanCounter(this); 
    } catch (IOException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } catch (XmlPullParserException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 
    showDialog(TUTORIAL); 
} 
@Override 
public boolean onKeyDown(int keyCode,KeyEvent e){ 
    if (keyCode == 82){ 

     if (viewDriverID.equals("hv")){ 
      hv.removeHV(); 
     } 
     else if (viewDriverID.equals("cv")){ 
      cv.removeCV(); 
     } 
     else if (viewDriverID.equals("mv")){ 
     return true; 
     } 
     else if (viewDriverID.equals("pcv")){ 
      return true; 
     } 

     if(man.getAddedState() == 0){ 

     //Show the manual code... 
     System.out.println("View we're coming from: " + this.getVDID()); 
     Log.e("me", "man.getaddedstate does equal 0, should be about to makeMan"); 

     man.makeMan();  
    } 

     else if(man.getAddedState() == 2){ 
     man.removeMan(); 
     man.removeMan2(); 
     man.setAddedState(1); 
    } 
     else if(man.getAddedState() == 1){ 
     System.out.println("View we're coming from: " + this.getVDID()); 
     man.addMan(); 
    } 
    } 
    return true; 
} 
@Override 
protected Dialog onCreateDialog(int id) { 
    //alerts ommitted for space 
} 

//Used to track the semantic context of what the Activity is displaying 
//Getters/setters for external access ommitted 

@Override 
protected void onStart(){ 
    super.onStart(); 
    Log.d("me","ultimap started!"); 
} 
@Override 
protected void onPause() { 
    super.onPause(); 
    Log.d("me","ultimap paused!"); 
    if (mgl.getGLview() != null){ 
      mgl.getGLview().onPause(); 
     } 
    if (draw.getGLV() != null){ 
     draw.getGLV().onPause(); 
    } 
} 
@Override 
protected void onResume() { 
    super.onResume(); 
    Log.d("me","ultimap resumed!"); 
    stalk.killListener(); 
    if (mgl.getGLview() != null){ 

      mgl.getGLview().onResume(); 
      Log.d("me", "mgl.getGLview is NOT null on resume"); 
     } 
    else if (mgl.getGLview() == null){ 
     mgl.initGL(); 
     mgl.getGLview().onResume(); 
     Log.d("me", "mgl.getGLview is null on resume"); 
    } 
    if (draw.getGLV() != null){ 
     draw.getGLV().onResume(); 
     Log.d("me", "draw.getGLV is NOT null on resume"); 
    } 
    else if (draw.getGLV() == null && draw.getHGL() != null){ 
      draw.pcvInit(); 
      Log.d("me", "draw.getGLV is null on resume"); 
    } 
    if (hv.getMV() != null && hv.getMV().getGLV() != null){ 
      hv.getMV().getGLV().onResume(); 
      Log.d("me", "map.getGLV is NOT null on resume"); 
     } 
     else if (hv.getMV() != null && hv.getMV().getGLV() == null && 
hv.getMV().getHGL() != null){ 
      hv.getMV().mvInit(); 
       Log.d("me", "map.getGLV is null on resume"); 
     } 
} 
@Override 
protected void onStop() { 
    super.onStop(); 
    //feed.getSP().release(); 
    Log.d("me","ultimap stopped!"); 
} 

@Override 
protected void onRestart(){ 
    super.onRestart(); 
    Log.d("me","ultimap restarted!"); 
    if (mgl != null){ 
      mgl.initGL(); 

     } 
} 
@Override 
protected void onDestroy(){ 
    super.onDestroy(); 
    Log.d("me","ultimap destroyed!"); 
    mgl.disposeTextures(); 
    if (feed.getSP() != null && feed.getSID() != 0 && feed.getLoaded() == 
true){ 
     feed.getSP().unload(feed.getSID()); 
     feed.getSP().release(); 
    } 
} 
}

教程視圖管理器類：

/* 
* This class defines an in-app manual which is callable/dismissable 
* in a non-invasive way... 
* 
* http://www.codeproject.com/KB/android/ViewFlipper_Animation.aspx 
*http://developer.android.com/reference/android/widget/ 
*ViewFlipper.html#ViewFlipper%28android.content.Context%29 
* http://developer.android.com/resources/articles/avoiding-memory-leaks.html 
*/ 
package com.ai.ultimap.views; 
//imports ommitted 
public class Manual extends View implements OnItemClickListener{ 
private UltiMapActivity hUMA; 
private ListView lv1; 
private ListAdapter la; 
private LayoutInflater mInflater; 
private Vector<RowData> data; 
private TextView tv; 
private RelativeLayout holderRL; 
private View v; 
private View v2; 
private int addedState = 0; //tracks whether or not a view has been instantiated, 
    //and if so whether or not it is the currently visible view 
private int addedState2 = 0; 

//Grid View stuff 
private GridView helpGrid; 

//ViewFlipper stuff 
private ViewFlipper vf; 
private TextView tutTV; 
private String mapTutString = "Map View Tutorial Part: "; 
private String pcTutString = "Path Creator Tutorial Part: "; 
private String tutType; 
private TextView counterTV; 
private int partCounter = 1; 
private float oldTouchValue = 0.0f; 
private boolean searchOk = true; 
private ImageView floatingImage; 

public Manual(UltiMapActivity hAct){ 
    super(hAct); 
    hUMA = hAct; 
    holderRL = new RelativeLayout(hUMA); 
    v = new View(hUMA); 
    floatingImage = new ImageView(hUMA); 
} 
//Here we summon and populate the grid view 
    public void makeMan(){ 
     if (addedState == 0){ 
      Log.e("me", "in makeMan"); 
     mInflater = (LayoutInflater) 
hUMA.getSystemService(Activity.LAYOUT_INFLATER_SERVICE); 
     hUMA.addContentView(holderRL, new 
LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT)); 
     v = mInflater.inflate(R.layout.helpgrid, holderRL, false); 
     helpGrid = (GridView) v.findViewById(R.id.manGV); 
     helpGrid.setAdapter(new ImageAdapter(hUMA)); 
     hUMA.addContentView(v, new 
LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT)); 
     helpGrid.setOnItemClickListener(this); 
     addedState = 2; 
     } 

    } 

public void addMan(){ 
    if (v != null && addedState == 1){ 
     v.setVisibility(VISIBLE); 
     v.bringToFront(); 
     addedState = 2; 
    } 
} 
public void addMan2(){ 
    if (v2 != null && addedState2 == 1){ 
     v2.setVisibility(VISIBLE); 
     v2.bringToFront(); 
     addedState2 = 2; 
    } 
} 
public void removeMan(){ 
    if (v != null && addedState == 2){ 
     v.setVisibility(GONE); 
     addedState = 1; 
     String s = hUMA.getVDID(); 
     if (s.equals("hv")){ 
      hUMA.getHome().addHV(); 
      Log.d("me", "add hjomeview called from anual"); 
      Log.d("me", "hv addedstate : " + 
hUMA.getHome().getAddedState()); 
     } 
     else if (s.equals("cv")){ 
      hUMA.getConfig().addCV(); 
     } 
     else if (s.equals("mv")){ 
      hUMA.getHome().getMV().mvInit(); 
     } 
     else if (s.equals("pcv")){ 
      hUMA.getDraw().pcvInit(); 
     } 
    } 
} 
public void removeMan2(){ 
    if (v2 != null && addedState2 == 2){ 
     v2.setVisibility(GONE); 
     addedState2 = 1; 
     String s = hUMA.getVDID(); 
     if (s.equals("hv")){ 
      hUMA.getHome().addHV(); 
      Log.d("me", "add hjomeview called from manual"); 
      Log.d("me", "hv addedstate : " + 
hUMA.getHome().getAddedState()); 
     } 
     else if (s.equals("cv")){ 
      hUMA.getConfig().addCV(); 
     } 
     else if (s.equals("mv")){ 
      hUMA.getHome().getMV().mvInit(); 
     } 
     else if (s.equals("pcv")){ 
      hUMA.getDraw().pcvInit(); 
     } 
    } 
} 

//addedstate getters and setters ommitted for space 

@Override 
    public boolean onTouchEvent(MotionEvent touchevent) { 

     switch (touchevent.getAction()) 
     { 
      case MotionEvent.ACTION_DOWN: 

      { 
       System.out.println("received a touch down at " + touchevent.getX() 
+ "," + touchevent.getY()); 
       oldTouchValue = touchevent.getX(); 
       if(this.searchOk==false) return false; 
       float currentX = touchevent.getX(); 
       if (currentX > (vf.getWidth()/2)) 
       { 
        vf.setInAnimation(AnimationHelper.inFromRightAnimation()); 
        vf.setOutAnimation(AnimationHelper.outToLeftAnimation()); 
        vf.showNext(); 
        if (partCounter <= 3 && partCounter >= 1){ 
         partCounter++; 
        } 
        else if (partCounter == 4){ 
         partCounter = 1; 
        } 
        else{ 
         Log.e("me", "partCounter got past 4..."); 
        } 
        if(tutType.equals("map")){ 
         counterTV.setText(mapTutString + partCounter); 
        } 
        else if(tutType.equals("pc")){ 
         counterTV.setText(pcTutString + partCounter); 
        } 
        else{ 
         Log.e("me","not getting valid tutType string"); 
        } 
       } 
       if (currentX <= (vf.getWidth()/2)) 
       { 
        vf.setInAnimation(AnimationHelper.inFromLeftAnimation()); 
        vf.setOutAnimation(AnimationHelper.outToRightAnimation()); 

        vf.showPrevious(); 
        if (partCounter >= 2 && partCounter <= 4){ 
         partCounter--; 
        } 
        else if (partCounter == 1){ 
         partCounter = 4; 
        } 
        else{ 
         Log.e("me", "partCounter got below 1..."); 
        } 
        if(tutType.equals("map")){ 
         counterTV.setText(mapTutString + partCounter); 
        } 
        else if(tutType.equals("pc")){ 
         counterTV.setText(pcTutString + partCounter); 
        } 
        else{ 
         Log.e("me","not getting valid tutType string"); 
        } 

       } 

       break; 
      } 
      case MotionEvent.ACTION_UP: 
      { 
       //nothing to do here 
      } 
     } 
     return false; 
    } 

public void setUserText(String str){ 
    tv.setText(str); 
} 

private class CustomTV extends TextView{ 

    private String content = ""; 
    public CustomTV(Context c, String str){ 
     super(c); 
     content = str; 
     this.setText(content); 
    } 
} 

/** 
* Data type used for custom adapter. Single item of the adapter.  
*/ 
private class RowData { 
    protected String mItem; 
     protected String mDescription; 
     RowData(String item, String description){ 
     mItem = item; 
     mDescription = description;    
    } 

     @Override 
     public String toString() { 
       return mItem + " " + mDescription; 
     } 
} 

private class CustomAdapter extends ArrayAdapter<RowData> { 

    public CustomAdapter(Context context, int resource, 
        int textViewResourceId, List<RowData> objects) { 
      super(context, resource, textViewResourceId, objects); 

    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 
      ViewHolder holder = null; 

      //widgets displayed by each item in your list 
      TextView item = null; 
      TextView description = null; 

      //data from your adapter 
      RowData rowData= getItem(position); 


      //we want to reuse already constructed row views... 
      if(null == convertView){ 
        convertView = mInflater.inflate(R.layout.custom_row, null); 
        holder = new ViewHolder(convertView); 
        convertView.setTag(holder); 
      } 
      holder = (ViewHolder) convertView.getTag(); 
      item = holder.getItem(); 
      item.setText(rowData.mItem); 
      description = holder.getDescription();   
      description.setText(rowData.mDescription); 
      return convertView; 
    } 
} 

/** 
* Wrapper for row data. 
* 
*/ 
private class ViewHolder {  
private View mRow; 
private TextView description = null; 
private TextView item = null; 

    public ViewHolder(View row) { 
    mRow = row; 
    } 

    public TextView getDescription() { 
      if(null == description){ 
        description = (TextView) mRow.findViewById(R.id.cbox); 
      } 
      return description; 
    } 

    public TextView getItem() { 
      if(null == item){ 
        item = (TextView) mRow.findViewById(R.id.cbox2); 
      } 
      return item; 
    }  
} 

@Override 
public void onItemClick(AdapterView<?> arg0, View arg1, int position, long id) { 

v.setVisibility(GONE); 
if (addedState2 == 0){ 
hUMA.addContentView(this,DefineLayoutParams.getParams(DefineLayoutParams.getMM())); 
//this is why the onTouch only starts lsitening at this point 
if (position == 0){ 
v2 = mInflater.inflate(R.layout.flipper, holderRL, false); 
vf = (ViewFlipper) v2.findViewById(R.id.manFlipperVF); 
tutTV = (TextView) v2.findViewById(R.id.manDescriptionTV); 
counterTV = (TextView) v2.findViewById(R.id.mapviewtutCounterTV); 
tutTV.setText("Map View Instructions: ..."); 
counterTV.setText(mapTutString + partCounter); 
tutType = "map"; 
} 
else if (position == 1){ 
    v2 = mInflater.inflate(R.layout.flipperpc, holderRL, false); 
    vf = (ViewFlipper) v2.findViewById(R.id.manFlipperpcVF); 
    tutTV = (TextView) v2.findViewById(R.id.manDescriptionpcTV); 
    counterTV = (TextView) v2.findViewById(R.id.manFlipperCounterpcTV); 
    tutTV.setText("Path Creator Tutorial:..."); 
    counterTV.setText(pcTutString + partCounter); 
    tutType = "pc"; 
} 
addedState2 = 2; 
hUMA.addContentView(v2, DefineLayoutParams.getParams(DefineLayoutParams.getWW())); 
} 
else if(addedState2 == 1){ 
    v2.setVisibility(VISIBLE); 
    addedState2 = 2; 
} 
} 
public String getTutType(){ 
return tutType; 
} 
}

教程查看翻轉XML：

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 

> 
<ScrollView 
android:id="@+id/manDerscriptionSV" 
android:layout_width="match_parent" 
android:layout_height="200px" 
> 
<TextView 
android:id="@+id/manDescriptionTV" 
android:text="Coming Soon..." 
android:layout_width="match_parent" 
android:layout_height="wrap_content" 
/> 
</ScrollView> 
<TextView 
android:id="@+id/mapviewtutCounterTV" 
android:layout_width="match_parent" 
android:layout_height="wrap_content" 
android:text="Map View Tutorial Part: " 
android:gravity="center" 
android:layout_below="@id/manDerscriptionSV" 
/> 
<ViewFlipper 
android:id="@+id/manFlipperVF" 
android:layout_width="match_parent" 
android:layout_height="wrap_content" 
android:layout_below="@id/mapviewtutCounterTV" 
> 
<ImageView 
    android:id="@+id/mapviewtut1" 
    android:src="@drawable/mapviewtutflipper1" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    /> 
<ImageView 
    android:id="@+id/mapviewtut2" 
    android:src="@drawable/mapviewtutflipper2" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    /> 
<ImageView 
    android:id="@+id/mapviewtut3" 
    android:src="@drawable/mapviewtutflipper3" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    /> 
<ImageView 
    android:id="@+id/mapviewtut4" 
    android:src="@drawable/mapviewtutflipper4" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    /> 


</ViewFlipper> 
</RelativeLayout>

感謝， CCJ

來源

2011-12-14 CCJ

非常好的問題。 – Mob

作爲這個方向的部分領導者：Android上的每個進程都有自己的虛擬機實例，即自己的GC。 – BRFennPocock

保持對象引用比您需要的時間更長通常不是一個好主意。諸如'ViewInflator'之類的東西以及「xml I \ O」註釋下的變量在我看來就像是臨時使用的東西，然後可以被丟棄。如果可能，請刪除這些字段並將它們設置爲局部變量，以便儘快進行垃圾回收。 –

究竟是什麼觸發了Android中的GC？

這是SDK開發人員不應該擔心的內部實現細節。

我見過的其他虛擬機實現通常允許一定比例的系統內存在GC接收到運行信號之前分配給應用程序。

我會對此表示贊同。 Java不像這樣。 JVM並不關心繫統內存的多少 - 它只關心其自身虛擬機的潛在堆大小（例如，-Xmx）。

然而掃描下面的logcat似乎顯示的Dalvik GC運行至少部分往往

正確的。特別是在較新版本的Android中，GC可以在自己的線程中同時運行，而不是早先採用的「停止世界」方法。

這對我來說沒有任何意義，因爲GC最近運行並沒有進行任何分配，因爲它應該在3MB容量（256 MB）之內引入VM。

您的虛擬機擁有256MB的堆空間是非常不可能的。取決於您的設備，它可能低至16MB。此外，Android沒有壓縮GC算法，所以即使您的可用空間超過3MB，也可能沒有連續的3MB塊。

這就是爲什麼它是要麼recycle()您Bitmap對象重要或嘗試重用他們（例如，BitmapOptionsinBitmap，在API級別11）。

此外，您可以使用DDMS創建一個堆轉儲和MAT來檢查它，以更準確地確定您的內存正在發生什麼，以及誰持有什麼。這在Android 3.0+上效果更好，因爲MAT將能夠更準確地在這些版本中報告Bitmap內存。

是否只有一小部分的256 MB系統RAM在虛擬機崩潰之前實際提供給VM？

是的。它被稱爲堆。Android設備具有堆大小限制。通常情況下，它在16-48MB範圍內，具體取決於Android操作系統版本和屏幕分辨率。

難道是位圖加載過程有它自己的內存分配上限嗎？

不，它使用相同的堆大小預算。從Android 3.0開始，它確實將內存從與其他Dalvik對象使用相同的堆中加載 - 以前，它使用堆外部的系統RAM塊，但是該空間是根據堆的大小預算計算的。

但不知道到底是什麼原因引發的Dalvik GC我們仍然將非常多的信心在OS和谷歌的業績含糊討論最佳實踐

生活，因爲他們說，那張。

能否GC狀態（例如，「大約跑」，「跑」，「運行完畢」）從代碼追蹤，以便大資源分配可能會計劃圍繞戰略性可用內存？ ...我想知道是否有支持的API調用可以依賴生產代碼（不僅僅是調試）來跟蹤垃圾收集器的準確狀態。

號

是GC總是全系統的，或者可以單獨的線程（如遊戲專用渲染線程）逃脫引起GC的潛在性能滯後的問題？

GC對於任何虛擬機都不是「系統範圍」的。 GC始終在VM內。

在較新版本的Android上，GC是併發的，因此在正常情況下不會實質性阻塞任何線程。在較舊版本的Android上，GC會停下來，並會影響所有線程。對於Android 3.0來說，這個變化是明確的 - 我的記憶模糊了併發GC是否已經在Android 2.3版本中。 2011年有一篇關於Android內存管理的Google I | O介紹，您可能希望觀看。

這會使VM崩潰嗎？或者有沒有某種方法可以自動處理這種極端情況以避免崩潰VM？

Android應在提高OutOfMemoryException之前強制立即GC。根據我以前的paragaraph，這種情況不符合「正常情況」。

來源

2011-12-14 19:02:12 CommonsWare

感謝您的回覆！你知道JNI如何與Dalvik VM內存使用聯繫起來嗎？本機代碼應該管理自己的內存，但是內存是否與應用程序的堆空間預算相比較？如果是這樣，如果該線程嘗試分配太多或者會出現這種情況（最終/可能）導致系統崩潰，那麼可以使用本機線程分配的Android無力內存嗎？ – CCJ

@CCJ：「內存是根據應用程序的堆空間預算計算的嗎？」 - 如果它是真正的本地內存（例如'malloc（）'），那麼我的理解是它不計入堆限制。但是，我不是JNI/NDK專家。 – CommonsWare

嗯......好的，我必須進一步研究這個問題。謝謝！ – CCJ

Android GC注意事項 - GC何時運行，並且可以從代碼跟蹤其運行狀態？

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