繪製筆劃

如要達到最佳繪圖效能，請使用 InProgressStrokesView 類別的 startStroke()、addToStroke() 和 finishStroke() 方法，並將 MotionEvent 物件做為輸入內容。

  1. 設定 UI 元件

    將 InProgressStrokesView 整合至檢視區塊階層。 

    <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. 例項化 InProgressStrokesView

    在活動或片段的 [onCreate()][ink-draw-include6] 方法中，取得 InProgressStrokesView 的參照，並建立觸控事件監聽器來管理使用者輸入內容。

    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. 處理觸控事件

    建立 UI 元件後，您現在可以根據觸控事件啟動繪圖。

    MotionEvent 動作

    InProgressStrokesView 方法

    說明

    ACTION_DOWN

    startStroke()

    開始顯示筆劃

    ACTION_MOVE

    addToStroke()

    繼續算繪筆劃

    ACTION_UP

    finishStroke()

    完成筆劃算繪

    ACTION_CANCEL 或 FLAG_CANCELED

    cancelStroke()

    實作防手掌誤觸功能；取消筆觸

    		 

    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. 處理完成的筆劃

    呼叫 finishStroke() 時，系統會將筆劃標示為完成。不過，最終程序不會立即生效。筆劃已完整處理，在呼叫 finishStroke() 後不久即可供應用程式存取，尤其是在沒有其他進行中的筆劃時。這樣可確保所有繪圖作業在筆劃傳送給用戶端前都已完成「完成」。

    如要擷取已完成的筆劃，有兩種方法可供選擇：

    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)
  }
}

    擷取完成的筆劃後，您可以使用 ViewStrokeRenderer 做為建構在 CanvasStrokeRenderer 之上的高階抽象概念。這可進一步簡化檢視區塊階層中的轉譯程序。

    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, ...
    }
  }
}