Question

我不想创建一个新的View对象，我已经在我的XML中定义了一个简单的View，我只想在它上面画一些条。

在XML中，我有一个空白的LinearLayout包含：

<View
    android:id="@+id/bars"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/grey" />

然后是我必须处理的代码。在这个例子中，我只是通过绘制一个小的蓝色圆圈来测试它：

View bars = (View) this.findViewById(R.id.bars);

Bitmap b = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(b);

mPaint.setColor(Color.BLUE);
c.drawCircle(5, 5, 8, mPaint);

bars.draw(c);

当我尝试设置颜色时，我得到的错误是NullPointerException。如果我拿出那条线，那么当我尝试绘制圆圈时我会收到错误。我怎么能做我想做的事？

编辑 - 错误日志（我拿出了setColor）：

05-19 00:56:14.100: E/AndroidRuntime(2422): FATAL EXCEPTION: main
05-19 00:56:14.100: E/AndroidRuntime(2422): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.aheadstudios.talkalytics/com.aheadstudios.talkalytics.ViewStatsPrototype}: java.lang.NullPointerException
05-19 00:56:14.100: E/AndroidRuntime(2422):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2308)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2358)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at android.app.ActivityThread.access$600(ActivityThread.java:153)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1247)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at android.os.Looper.loop(Looper.java:137)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at android.app.ActivityThread.main(ActivityThread.java:5227)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at java.lang.reflect.Method.invokeNative(Native Method)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at java.lang.reflect.Method.invoke(Method.java:511)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at dalvik.system.NativeStart.main(Native Method)
05-19 00:56:14.100: E/AndroidRuntime(2422): Caused by: java.lang.NullPointerException
05-19 00:56:14.100: E/AndroidRuntime(2422):     at android.graphics.Canvas.drawCircle(Canvas.java:961)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at com.aheadstudios.talkalytics.MultiStatsData.commonSetup(MultiStatsData.java:68)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at com.aheadstudios.talkalytics.MultiStatsData.<init>(MultiStatsData.java:50)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at com.aheadstudios.talkalytics.ViewStatsPrototype.setupMultiStatsData(ViewStatsPrototype.java:48)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at com.aheadstudios.talkalytics.ViewStatsPrototype.onCreate(ViewStatsPrototype.java:43)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at android.app.Activity.performCreate(Activity.java:5104)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
05-19 00:56:14.100: E/AndroidRuntime(2422):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2262)
05-19 00:56:14.100: E/AndroidRuntime(2422):     ... 11 more

Answer 1

mPaint = new Paint（）;

然后代替bars.draw（c）

添加

bars.setBackgroundDrawable（new BackgroundDrawable（b））;

如何在XML定义的视图中使用canvas绘制函数

1 个答案: