我正在做一个应用程序,它将显示 ontouch 的位置。我的代码如下我编辑了我的代码。公共类 AndroidTabLayoutAcActivity 扩展 Activity{
DemoView demoview1 ;
DemoView2 demoview2;
DemoView3 demoview3;
DemoView4 demoview4;
LowerView lowerview;
float d,b;
//ViewFlipper c;
//ViewFlipper a;
String text="Oxygen";
String text1="Carbon";
String text2="Phosphate";
String text3="Hydrogen";
//Called when the activity is first created.
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
demoview1 = new DemoView(this);
setContentView(demoview1);
demoview1.requestFocus();
}
public class DemoView extends View implements OnTouchListener{
String n1="";
String n2="";
Canvas canvas;
public DemoView(Context context){
super(context);
setOnTouchListener(this);
}
public boolean onTouch(View view, MotionEvent event) {
// if(event.getAction() != MotionEvent.ACTION_DOWN)
// return super.onTouchEvent(event);
d = event.getX();
b = event.getY();
n1=Float.toString(d);
n2=Float.toString(b);
onDraw(canvas);
return true;
}
@Override protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
int x = 150;
int y = 100;
Paint paint = new Paint();
paint.setStyle(Paint.Style.FILL);
// make the entire canvas white
paint.setColor(Color.CYAN);
canvas.drawPaint(paint);
paint.setAntiAlias(true);
paint.setColor(Color.RED);
canvas.drawCircle(x-24, y+30, 11, paint);
paint.setColor(Color.WHITE);
canvas.drawCircle(x+11, y-11, 7, paint);
canvas.drawCircle(x+6, y+48, 7, paint);
canvas.drawCircle(x+21, y+43, 7, paint);
//carbon molecule
paint.setColor(Color.BLACK);
canvas.drawCircle(x, y, 11, paint);
canvas.drawCircle(x-11, y+19, 11, paint);
canvas.drawCircle(x, y+38, 11, paint);
canvas.drawCircle(x+20, y+30, 11, paint);
canvas.drawCircle(x-11, y-19, 11, paint);
//hydrogen molecule
paint.setColor(Color.WHITE);
canvas.drawCircle(x-25, y-12, 7, paint);
canvas.drawCircle(x+2, y-27, 7, paint);
canvas.drawCircle(x-20, y+9, 7, paint);
canvas.drawCircle(x-10, y+45, 7, paint);
canvas.drawCircle(x-34, y+40, 7, paint);
canvas.drawCircle(x+51, y+18, 7, paint);
canvas.drawCircle(x-33, y-52, 7, paint);
//oxygen molecule
paint.setColor(Color.RED);
canvas.drawCircle(x+41, y+30, 11, paint);
canvas.drawCircle(x+20, y+9, 11, paint);
canvas.drawCircle(x-23, y-37, 11, paint);
canvas.drawText(n1, x+100, y+100, paint);
canvas.drawText(n2, x+100, y+100, paint);
}
}
}
我的日志 cat 文件显示以下错误,但我不明白为什么它显示以下错误..
05-07 12:26:31.354: E/AndroidRuntime(385): FATAL EXCEPTION: main
05-07 12:26:31.354: E/AndroidRuntime(385): java.lang.NullPointerException
05-07 12:26:31.354: E/AndroidRuntime(385): at com.example.an.AndroidTabLayoutAcActivity$DemoView.onDraw(AndroidTabLayoutAcActivity.java:150)
05-07 12:26:31.354: E/AndroidRuntime(385): at com.example.an.AndroidTabLayoutAcActivity$DemoView.onTouch(AndroidTabLayoutAcActivity.java:136)
05-07 12:26:31.354: E/AndroidRuntime(385): at android.view.View.dispatchTouchEvent(View.java:3762)
05-07 12:26:31.354: E/AndroidRuntime(385): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:863)
05-07 12:26:31.354: E/AndroidRuntime(385): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:863)
05-07 12:26:31.354: E/AndroidRuntime(385): at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1671)
05-07 12:26:31.354: E/AndroidRuntime(385): at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1107)
05-07 12:26:31.354: E/AndroidRuntime(385): at android.app.Activity.dispatchTouchEvent(Activity.java:2086)
05-07 12:26:31.354: E/AndroidRuntime(385): at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1655)
05-07 12:26:31.354: E/AndroidRuntime(385): at android.view.ViewRoot.handleMessage(ViewRoot.java:1785)
05-07 12:26:31.354: E/AndroidRuntime(385): at android.os.Handler.dispatchMessage(Handler.java:99)
05-07 12:26:31.354: E/AndroidRuntime(385): at android.os.Looper.loop(Looper.java:123)
05-07 12:26:31.354: E/AndroidRuntime(385): at android.app.ActivityThread.main(ActivityThread.java:4627)
05-07 12:26:31.354: E/AndroidRuntime(385): at java.lang.reflect.Method.invokeNative(Native Method)
05-07 12:26:31.354: E/AndroidRuntime(385): at java.lang.reflect.Method.invoke(Method.java:521)
05-07 12:26:31.354: E/AndroidRuntime(385): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
05-07 12:26:31.354: E/AndroidRuntime(385): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
05-07 12:26:31.354: E/AndroidRuntime(385): at dalvik.system.NativeStart.main(Native Method)