绘制笔画

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

  1. 设置界面组件

    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. 处理轻触事件

    界面组件已建立完毕,现在您可以根据触摸事件发起绘制操作了。

    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()

    最终渲染笔触

    ACTION_CANCELFLAG_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,最终确定流程并非瞬间完成。在调用 finishStroke() 后,系统会立即处理笔触,并在没有其他笔触正在处理时,让应用能够访问该笔触。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, ...
        }
      }
    }