这是我用于动画绘制的类，它需要曲线的起点和终点以及要渲染的曲线数。
public class DrawIt extends View {
Context context;
int[] z;
int[] k;
Path[] patharr;
Path[] drawarr;
Paint paint = new Paint();
Paint paint2 = new Paint();
Paint paint3 = new Paint();
Random r = new Random();
float x1;
float y1;
float x3;
float y3;
float x2;
float y2;
int ref;
public boolean finito = false;
public DrawIt(Context context, int a, int b, int c, int d,
final int num) {
super(context);
this.context = context;
setBackgroundResource(com.example.test.R.drawable.endturn);
this.ref = num;
x1 = a;
y1 = b;
x3 = c;
y3 = d;
if (x1 < x3) {
x2 = (x1 + x3) / 2 - 50;
} else {
x2 = (x1 + x3) / 2 + 50;
}
y2 = (y1 + y3) / 2 - 350;
paint.setAntiAlias(true);
paint.setAlpha(255);
paint.setStrokeWidth(2);
paint.setColor(Color.WHITE);
paint.setStyle(Style.STROKE);
paint.setPathEffect(new DashPathEffect(new float[] { 2, 4 }, 50));
paint2.setAntiAlias(true);
paint2.setAlpha(55);
paint2.setStrokeWidth(1);
paint2.setColor(Color.WHITE);
paint2.setStyle(Style.FILL);
paint3.setAntiAlias(true);
paint3.setAlpha(255);
paint3.setStrokeWidth(2);
paint3.setColor(Color.RED);
paint3.setStyle(Style.STROKE);
drawarr = new Path[num];
patharr = new Path[num];
z = new int[num];
k = new int[num];
for (int p = 0; p < num; p++) {
k[p] = r.nextInt(50 - 1) - 1;
z[p] = r.nextInt(50 - 1) - 1;
patharr[p] = new Path();
patharr[p].moveTo(x1, y1);
patharr[p].quadTo(x2, y2, x3 + k[p], y3 + z[p]);
}
final long DRAW_TIME = 800;
CountDownTimer timer = new CountDownTimer(DRAW_TIME, 100) {
PathMeasure[] measarr = new PathMeasure[num];
Path[] segmarr = new Path[num];
float[] startarr = new float[num];
float[] lengtharr = new float[num];
@Override
public void onTick(long millisUntilFinished) {
for (int p = 0; p < num; p++) {
measarr[p] = new PathMeasure();
segmarr[p] = new Path();
measarr[p].setPath(patharr[p], false);
startarr[p] = 0;
}
float percent = ((float) (DRAW_TIME - millisUntilFinished))
/ (float) DRAW_TIME;
for (int p = 0; p < num; p++) {
lengtharr[p] = measarr[p].getLength() * percent;
}
for (int p = 0; p < num; p++) {
measarr[p].getSegment(startarr[p], lengtharr[p],
segmarr[p], true);
}
for (int p = 0; p < num; p++) {
startarr[p] = lengtharr[p];
}
for (int p = 0; p < num; p++) {
drawarr[p] = new Path();
drawarr[p].addPath(segmarr[p]);
}
invalidate();
}
@Override
public void onFinish() {
for (int p = 0; p < num; p++) {
measarr[p].getSegment(startarr[p], measarr[p].getLength(),
segmarr[p], true);
}
for (int p = 0; p < num; p++) {
drawarr[p].addPath(segmarr[p]);
}
if (measarr[0].getSegment(startarr[0], measarr[0].getLength(),
segmarr[0], false)) {
finito = true;
}
invalidate();
}
};
timer.start();
}
@Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
Log.d("Costruttore", "" + drawarr[0]);
for (int p = 0; p < drawarr.length; p++) {
canvas.drawPath(drawarr[p], paint);
}
if (finito == true) {
for (int m = 0; m < drawarr.length; m++) {
canvas.drawCircle(x3 + k[m], y3 + z[m], 10, paint2);
canvas.drawCircle(x3 + k[m], y3 + z[m], 10, paint3);
}
}
}
}
@Override
public void onTick(long millisUntilFinished) {
if (l < players.length) {
while (l < players.length && players[l].mess.equals(".")) {
l++;
}
if (l >= players.length) {
this.cancel();
} else {
azioni.setText(players[l].mess);
players[l].vista = new DrawIt(TurnActivity.this, x1,y1,x2,y2);
addContentView(players[l].vista, layout);
l++;
}
}
}
这导致Ondraw上出现NullPointerException。我不明白为什么。我是Android的新手，也许这可能是了解更多关于View和使用CountDownTimer制作的动画的机会。
这是Logcat：
04-23 16:00:26.175: W/dalvikvm(1135): threadid=1: thread exiting with uncaught exception (group=0xa4dcab20)
04-23 16:00:26.179: E/AndroidRuntime(1135): FATAL EXCEPTION: main
04-23 16:00:26.179: E/AndroidRuntime(1135): Process: com.example.test, PID: 1135
04-23 16:00:26.179: E/AndroidRuntime(1135): java.lang.NullPointerException
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.GLES20Canvas.drawPath(GLES20Canvas.java:1059)
04-23 16:00:26.179: E/AndroidRuntime(1135): at com.example.test.DrawIt.onDraw(DrawIt.java:154)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.draw(View.java:14465)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.getDisplayList(View.java:13362)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.getDisplayList(View.java:13404)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.draw(View.java:14182)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.ViewGroup.drawChild(ViewGroup.java:3103)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2940)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.getDisplayList(View.java:13357)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.getDisplayList(View.java:13404)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.draw(View.java:14182)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.ViewGroup.drawChild(ViewGroup.java:3103)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2940)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.getDisplayList(View.java:13357)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.getDisplayList(View.java:13404)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.draw(View.java:14182)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.ViewGroup.drawChild(ViewGroup.java:3103)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2940)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.draw(View.java:14468)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.widget.FrameLayout.draw(FrameLayout.java:472)
04-23 16:00:26.179: E/AndroidRuntime(1135): at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:2326)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.getDisplayList(View.java:13362)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.View.getDisplayList(View.java:13404)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.HardwareRenderer$GlRenderer.buildDisplayList(HardwareRenderer.java:1570)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.HardwareRenderer$GlRenderer.draw(HardwareRenderer.java:1449)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.ViewRootImpl.draw(ViewRootImpl.java:2381)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.ViewRootImpl.performDraw(ViewRootImpl.java:2253)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1883)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.Choreographer.doCallbacks(Choreographer.java:574)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.Choreographer.doFrame(Choreographer.java:544)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.os.Handler.handleCallback(Handler.java:733)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.os.Handler.dispatchMessage(Handler.java:95)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.os.Looper.loop(Looper.java:136)
04-23 16:00:26.179: E/AndroidRuntime(1135): at android.app.ActivityThread.main(ActivityThread.java:5017)
04-23 16:00:26.179: E/AndroidRuntime(1135): at java.lang.reflect.Method.invokeNative(Native Method)
04-23 16:00:26.179: E/AndroidRuntime(1135): at java.lang.reflect.Method.invoke(Method.java:515)
04-23 16:00:26.179: E/AndroidRuntime(1135): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-23 16:00:26.179: E/AndroidRuntime(1135): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-23 16:00:26.179: E/AndroidRuntime(1135): at dalvik.system.NativeStart.main(Native Method)
04-23 16:00:27.983: I/Process(1135): Sending signal. PID: 1135 SIG: 9