Draw a stroke

为了实现最佳绘制性能，请使用 InProgressStrokesView 类的 startStroke()、addToStroke() 和 finishStroke() 方法，并将 MotionEvent 对象作为输入传递。

  1. 设置界面组件

    将 InProgressStrokesView 集成到视图层次结构中。 

    <FrameLayout>

  <ScrollView
    android:id="@+id/my_content"
    android:width="match_parent"
    android:height="match_parent"
    >
    <!-- Your content here. -->
  </ScrollView>

  <androidx.ink.authoring.InProgressStrokesView
    android:id="@+id/in_progress_strokes_view"
    android:width="match_parent"
    android:height="match_parent"
    />

</FrameLayout>

  2. 实例化 InProgressStrokesView

    在 activity 或 fragment 的 [onCreate()][ink-draw-include6] 方法中，获取对 InProgressStrokesView 的引用，并建立触摸监听器来管理用户输入。

    class MyActivity : View.OnTouchListener {
    private lateinit var contentView: ScrollView
    private lateinit var inProgressStrokesView: InProgressStrokesView
    private lateinit var predictor: MotionEventPredictor

    // ... other variables

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
      predictor = MotionEventPredictor.newInstance(contentView)
        contentView = findViewById(R.id.my_content)
        contentView.setOnTouchListener(touchListener)
        inProgressStrokesView = findViewById(R.id.in_progress_strokes_view)
    }

    // ... (touchListener implementation)
}

  3. 处理触摸事件

    创建界面组件后，您现在可以基于触摸事件启动绘制了。

    MotionEvent 操作

    InProgressStrokesView 方法

    说明

    ACTION_DOWN

    startStroke()

    开始绘制笔触

    ACTION_MOVE

    addToStroke()

    继续渲染笔画

    ACTION_UP

    finishStroke()

    完成描边渲染

    ACTION_CANCEL 或 FLAG_CANCELED

    cancelStroke()

    实现防手掌误触功能；取消笔触

    		 

    class MyActivity : View.OnTouchListener {
  private lateinit var contentView: ScrollView
  private lateinit var inProgressStrokesView: InProgressStrokesView

  private var pointerId = -1
  private var strokeId: InProgressStrokeId? = null
  private lateinit var predictor: MotionEventPredictor

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    contentView = findViewById(R.id.my_content)
    predictor = MotionEventPredictor.create(contentView)
    contentView.setOnTouchListener(touchListener)
    inProgressStrokesView = findViewById(R.id.in_progress_strokes_view)
  }

  private val touchListener = { view: View, event: MotionEvent ->
    predictor.record(event)
      when (event.actionMasked) {
        MotionEvent.ACTION_DOWN -> {
          // First pointer - treat it as inking.
          view.requestUnbufferedDispatch(event)
          val pointerIndex = event.actionIndex
          pointerIdToStrokeId[event.getPointerId(pointerIndex)] =
            inProgressStrokesView.startStroke(event, pointerId)
          return true
        }
        MotionEvent.ACTION_POINTER_DOWN -> {
          val stroke = strokeId ?: return false
          inProgressStrokesView.cancelStroke(stroke, event)
          strokeId = null
          pointerId = -1
          return false
        }
        MotionEvent.ACTION_MOVE -> {
          val predictedEvent = predictor.predict()
          try
          {
            for (pointerIndex in 0 until pointerCount) {
              val strokeId =
              pointerIdToStrokeId[event.getPointerId(pointerIndex)] ?: continue
              inProgressStrokesView.addToStroke(event, pointerId, strokeId, predictedEvent)
            } finally {
              predictedEvent?.recycle()
            }
          }
        }
        MotionEvent.ACTION_UP -> {
          val pointerIndex = event.actionIndex
          val strokeId =
            pointerIdToStrokeId[event.getPointerId(pointerIndex)] ?: return false
          inProgressStrokesView.finishStroke(event, pointerId, strokeId)
          return true
        }
        MotionEvent.ACTION_CANCEL -> {
          val pointerIndex = event.actionIndex
          val strokeId =
            pointerIdToStrokeId[event.getPointerId(pointerIndex)] ?: return false
          inProgressStrokesView.cancelStroke(strokeId, event)
          return true
        }
      }
    return false
  }
}

  4. 处理完成的笔画

    调用 finishStroke() 后，系统会将笔画标记为已完成。不过，最终敲定的过程不是即时完成的。描边已完全处理，在调用 finishStroke() 后不久（特别是没有其他正在进行的描边时）可供应用访问。这样可确保在将笔触作为已完成的操作传递给客户端之前，所有绘制操作均已完成。

    如需检索已完成的笔画，您有以下两种方法可选：

    class MyActivity : ComponentActivity(), InProgressStrokesFinishedListener {
  ...

  private val finishedStrokesState = mutableStateOf(emptySet<Stroke>())

  override fun onCreate(savedInstanceState: Bundle?) {
    ...
    inProgressStrokesView.addFinishedStrokesListener(this)
  }

  // ... (handle touch events)

  @UiThread
  override fun onStrokesFinished(strokes: Map<InProgressStrokeId, Stroke>) {
    finishedStrokesState.value += strokes.values
    inProgressStrokesView.removeFinishedStrokes(strokes.keys)
  }
}

    检索完完成的笔画后，您可以将 ViewStrokeRenderer 用作在 CanvasStrokeRenderer 之上构建的更高级别的抽象。这可以进一步简化视图层次结构中的渲染流程。

    class DrawingView(context: Context) : View(context) {
  private val viewStrokeRenderer = ViewStrokeRenderer(myCanvasStrokeRenderer, this)

  override fun onDraw(canvas: Canvas) {
    viewStrokeRenderer.drawWithStrokes(canvas) { scope ->
      canvas.scale(myZoomLevel)
      canvas.rotate(myRotation)
      canvas.translate(myPanX, myPanY)
      scope.drawStroke(myStroke)
      // Draw other objects including more strokes, apply more transformations, ...
    }
  }
}