1
最近，爲了將手機與無線傳感器網絡集成，我調整了一個類作爲活動以及從串口讀取並將一些讀數繪製成簡單的監聽器類基於畫布的視圖。 我最初嘗試使用更普通的消息處理程序和線程來構建一個線程畫布，該線程更新並使其無效，但存儲我需要繪製的讀數的類也正在關閉偵聽USB端口的線程。當時我無法得到它的工作，我決定我可能不需要不斷更新畫布，因爲我只需要用新的讀數更新它。視圖上的空指針
所以活動類如下。
public class Oscilloscope extends Activity implements MessageListener
Graph graph;
boolean guard=false;
MoteIF mote;
Data data;
String comm;
static String writeLog;
public Vector <Integer> arrayvals = new Vector<Integer>();
public Oscilloscope(String comm, String writelog)
{
this.comm = comm;
this.writeLog = writelog;
}
public Oscilloscope()
{
}
public void onCreate(Bundle b)
{
super.onCreate(b);
graph = new Graph(this);
this.setContentView(graph);
if(guard==false)
{
create("dummy:1",null).run();
}
}
synchronized public void messageReceived(int dest_addr, Message msg) {
if (msg instanceof OscilloscopeMsg) {
OscilloscopeMsg omsg = (OscilloscopeMsg)msg;
periodUpdate(omsg.get_version(), omsg.get_interval());
data.update(omsg.get_id(), omsg.get_count(), omsg.get_readings());
List temp1 = Arrays.asList(omsg.get_readings());
Vector<Integer> temp= new Vector<Integer>(temp1);
this.arrayvals = temp;
Paint p = new Paint();
p.setColor(Color.BLUE);
this.graph.update();
this.graph.invalidate();
}
}
public Oscilloscope create(String a, String b)
{
guard = true;
Oscilloscope os = new Oscilloscope(a,b);
os.guard = true;
return os;
}
不知道爲什麼它是我不能讓代碼括號在那裏正常工作，我道歉。 類中還有其他方法，但類本身的行爲應該是減去視圖部分，特別要注意消息接收方法，其中讀數以int數組讀取。 我的問題是，一旦onDraw方法被調用一次，然後調用messagereceived之後，圖形對象似乎是null，當我嘗試調用更新時，顯然會引發空指針。我可能沒有看到真正明顯的事情。 圖形代碼如下非常簡單：
public class Graph extends View
Paint paint= new Paint();
public float x;
public float y;
Vector<CoOrdinate> coVec = new Vector<CoOrdinate>();
public Graph(Context context) {
super(context);
}
public void onDraw(Canvas canvas)
{
Log.v("Line 28 Graph.java","Y: "+y+"X: "+x);
canvas.drawCircle(x, y, 2, paint);
Log.v(this.toString(),"onDraw in the graph");
}
public void update()
{
Log.v("Line 31 of Graph.java","");
x+=100;
y+=100;
paint.setColor(Color.GREEN);
}
}
任何幫助表示讚賞。謝謝。
02-11 19:03:00.933: DEBUG/AndroidRuntime(301): >>>>>>>>>>>>>> AndroidRuntime START <<<<<<<<<<<<<<
02-11 19:03:00.933: DEBUG/AndroidRuntime(301): CheckJNI is ON
02-11 19:03:02.012: DEBUG/AndroidRuntime(301): --- registering native functions ---
02-11 19:03:03.942: INFO/ActivityManager(60): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=graphAndroid.graphs/.Oscilloscope }
02-11 19:03:04.062: DEBUG/AndroidRuntime(301): Shutting down VM
02-11 19:03:04.082: DEBUG/jdwp(301): adbd disconnected
02-11 19:03:04.122: INFO/AndroidRuntime(301): NOTE: attach of thread 'Binder Thread #3' failed
02-11 19:03:04.263: INFO/ActivityManager(60): Start proc graphAndroid.graphs for activity graphAndroid.graphs/.Oscilloscope: pid=308 uid=10040 gids={1015}
02-11 19:03:05.263: INFO/ARMAssembler(60): generated scanline__00000077:03545404_00000004_00000000 [ 47 ipp] (67 ins) at [0x361990:0x361a9c] in 6676000 ns
02-11 19:03:05.493: INFO/System.out(308): Creating dummy source (dummy:1)
02-11 19:03:05.493: INFO/System.out(308): No Motes:1
02-11 19:03:05.503: VERBOSE/Line 129 Oscilloscope.java(308): Made it to here
02-11 19:03:05.503: VERBOSE/Line 135 Oscilloscope.java(308): Made it here
02-11 19:03:05.513: VERBOSE/Line 137 Oscilloscope.java(308): Made it here
02-11 19:03:05.513: VERBOSE/Line 114 MoteIF.java(308): Third constructor
02-11 19:03:05.513: VERBOSE/Line 121 MoteIF.java(308): Made it here
02-11 19:03:05.513: VERBOSE/Line 123 MoteIF.java(308): Made it here
02-11 19:03:05.523: VERBOSE/Line 127 MoteIF.java(308): Made it here
02-11 19:03:05.523: VERBOSE/Line 130 MoteIF.java(308): Made it here
02-11 19:03:05.523: VERBOSE/Line 69 PhoenixSource.java(308): Made it here
02-11 19:03:05.523: VERBOSE/Line 71 PhoenixSource.java(308): Made it here
02-11 19:03:05.523: VERBOSE/Line 74 PhoenixSource.java(308): Made it here
02-11 19:03:05.523: VERBOSE/Line 133 MoteIF.java(308): Made it here
02-11 19:03:05.523: VERBOSE/Line 138 MoteIF.java(308): Made it here
02-11 19:03:05.533: VERBOSE/Line 140 MoteIF.java(308): Made it here
02-11 19:03:05.543: VERBOSE/Line 142 MoteIF.java(308): Made it here
02-11 19:03:05.543: VERBOSE/Line 138 Oscilloscope.java(308): Made it here
02-11 19:03:05.543: VERBOSE/Line 140 Oscilloscope.java(308): Made it to here
02-11 19:03:05.783: VERBOSE/Line 28 Graph.java(308): Y: 0.0X: 0.0
02-11 19:03:05.793: VERBOSE/[email protected](308): onDraw in the graph
02-11 19:03:05.823: INFO/ActivityManager(60): Displayed activity graphAndroid.graphs/.Oscilloscope: 1679 ms (total 1679 ms)
02-11 19:03:07.543: INFO/System.out(308): SimulatedOscilloscopePacketSource moteId is 0
02-11 19:03:07.543: VERBOSE/1(308): A test, line 424 OscilloscopeMsg class
02-11 19:03:07.543: WARN/dalvikvm(308): threadid=7: thread exiting with uncaught exception (group=0x4001d800)
02-11 19:03:07.563: ERROR/AndroidRuntime(308): FATAL EXCEPTION: Thread-8
02-11 19:03:07.563: ERROR/AndroidRuntime(308): java.lang.NullPointerException
02-11 19:03:07.563: ERROR/AndroidRuntime(308): at graphAndroid.graphs.Oscilloscope.messageReceived(Oscilloscope.java:108)
02-11 19:03:07.563: ERROR/AndroidRuntime(308): at net.tinyos.message.Receiver.packetReceived(Receiver.java:210)
02-11 19:03:07.563: ERROR/AndroidRuntime(308): at net.tinyos.packet.PhoenixSource.dispatch(PhoenixSource.java:165)
02-11 19:03:07.563: ERROR/AndroidRuntime(308): at net.tinyos.packet.PhoenixSource.packetDipatchLoop(PhoenixSource.java:157)
02-11 19:03:07.563: ERROR/AndroidRuntime(308): at net.tinyos.packet.PhoenixSource.run(PhoenixSource.java:174)
02-11 19:03:07.613: WARN/ActivityManager(60): Force finishing activity graphAndroid.graphs/.Oscilloscope
02-11 19:03:07.932: WARN/IInputConnectionWrapper(129): showStatusIcon on inactive InputConnection
02-11 19:03:08.463: INFO/ARMAssembler(60): generated scanline__00000077:03515104_00000000_00000000 [ 33 ipp] (47 ins) at [0x36b288:0x36b344] in 746000 ns
John，請添加堆棧跟蹤。 – DJC 2011-02-11 18:53:39
抱歉，關於使用Logcat輸出編輯上面的那個。謝謝。 – 2011-02-11 19:07:22