添加自定义视图作为XML布局的视图

Question

方案如下:

我有一个活动RunTrainingWorkoutsView,它使用XML布局_run_workout.xml_,其中一些标签由CountDownTimer更新.工作良好...

现在,除了每秒通过onTick() CountDownTimer对象的回调方法更新的标签,我想在我的_run_workout.xml layout_中添加一个自定义表面视图,它将绘制一些每秒由同一onTick()方法更新的弧. .

我的run_workout.xml:

<training.timer.CounterClockView 
    android:id="@+id/counter_clock_surface"
    android:layout_width="300dp" 
    android:layout_height="240dp">
</training.timer.CounterClockView>

我的自定义View扩展了surfaceView

public class CounterClockView extends SurfaceView {

Paint paint = new Paint();
Paint paint2 = new Paint();

final RectF rect = new RectF();
final RectF rect2 = new RectF();

int counterArcAngle = 15;
//constructor
public CounterClockView(Context context, AttributeSet attributeSet) {
    super(context);

    //setting some paint properties...

    this.setBackgroundColor(Color.TRANSPARENT);

}

@Override
public void onDraw(Canvas canvas) {

    rect.set(50, 50, 150, 150);
    rect2.set(50, 50, 150, 150);

    this.layout(0, 0, 200, 200);

    canvas.drawArc(rect, -90, 360, false, paint);
    canvas.drawArc(rect2, -90, counterArcAngle, false, paint2);

}

扩展活动的主要类是使用以下代码在布局中获取对自定义surfaceView的引用:

//counterClockView  is declared outside of onCreate() as CounterClockView counterClockView;  

//later in onCreate(){....
counterClockView  = (CounterClockView) findViewById(R.id.counter_clock_surface);

问题是改变customView对象的成员变量的值(counterClockView)

counterClockView.counterArcAngle = 10;

将崩溃应用程序...

另外,从我的主要活动开始,我想调用invalidate()方法在更改counterArcAngle值后重做表面视图,但这会导致应用程序崩溃...

为什么不能创建counterClockView对象并将其引用到相同类型的xml布局元素并更改其外观,使其无效等？

编辑LogCat:

threadid=1: thread exiting with uncaught exception (group=0x40015560)

ERROR/AndroidRuntime(487): FATAL EXCEPTION: main

ERROR/AndroidRuntime(487): java.lang.RuntimeException: Unable to start activity ComponentInfo{training.timer/training.timer.RunTrainingWorkoutsView}: java.lang.NullPointerException

ERROR/AndroidRuntime(487):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
ERROR/AndroidRuntime(487):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
ERROR/AndroidRuntime(487):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
ERROR/AndroidRuntime(487):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
ERROR/AndroidRuntime(487):     at android.os.Handler.dispatchMessage(Handler.java:99)
ERROR/AndroidRuntime(487):     at android.os.Looper.loop(Looper.java:123)

ERROR/AndroidRuntime(487):     at android.app.ActivityThread.main(ActivityThread.java:3683)
ERROR/AndroidRuntime(487):     at java.lang.reflect.Method.invokeNative(Native Method)
ERROR/AndroidRuntime(487):     at java.lang.reflect.Method.invoke(Method.java:507)
ERROR/AndroidRuntime(487):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
ERROR/AndroidRuntime(487):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
ERROR/AndroidRuntime(487):     at dalvik.system.NativeStart.main(Native Method)
ERROR/AndroidRuntime(487): Caused by: java.lang.NullPointerException
ERROR/AndroidRuntime(487):     at training.timer.RunTrainingWorkoutsView.onCreate(RunTrainingWorkoutsView.java:72)
ERROR/AndroidRuntime(487):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
ERROR/AndroidRuntime(487):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
ERROR/AndroidRuntime(487):     ... 11 more

Answer 1

经过3天的攻击,我的头靠在墙上,谷歌搜索,stacOverflowing等我得到了它.

实际上,这是一个愚蠢的小事......

我的XML文件,我定义了包含一些常见的android视图(即textView和按钮)的布局和我的自定义视图CounterClockView:

<training.timer.CounterClockView 
android:id="@+id/counter_clock_surface"
android:layout_width="300dp" 
android:layout_height="240dp">

我必须增加一条线!

<training.timer.CounterClockView 
    xmlns:android="http://schemas.android.com/apk/res/android"   !!!
    android:id="@+id/counter_clock_surface"
    android:layout_width="300dp" 
    android:layout_height="240dp">
</training.timer.CounterClockView>

我不知道为什么这个命名空间行产生了如此巨大的差异,但它的效果很好!

现在,我可以在CountDownTimer()的每个onTick()上从我的主要活动更新我的自定义视图...

以下答案非常有用: findViewById()为布局XML中的自定义组件返回null,而不是其他组件