มุมมองที่กำหนดเอง

เหตุใดจึงต้องใช้มุมมองที่กำหนดเอง

การสืบทอดจาก View

class CircleProgressView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = 0
) : View(context, attrs, defStyleAttr) {

    var progress: Float = 0f
        set(value) {
            field = value.coerceIn(0f, 100f)
            invalidate()   // trigger redraw
        }

    // onMeasure and onDraw go here
}

onMeasure()

override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
    val desiredSize = 200  // dp → pixels
    val px = (desiredSize * resources.displayMetrics.density).toInt()

    val width  = resolveSize(px, widthMeasureSpec)
    val height = resolveSize(px, heightMeasureSpec)

    // Square: same width and height
    val size = minOf(width, height)
    setMeasuredDimension(size, size)
}

Paint — เครื่องมือวาด

class CircleProgressView ... : View(...) {

    // Create Paint in init, not in onDraw!
    private val backgroundPaint = Paint(Paint.ANTI_ALIAS_FLAG).apply {
        color = Color.LTGRAY
        style = Paint.Style.STROKE
        strokeWidth = 20f
        strokeCap = Paint.Cap.ROUND
    }

    private val progressPaint = Paint(Paint.ANTI_ALIAS_FLAG).apply {
        color = Color.parseColor("#6750A4")
        style = Paint.Style.STROKE
        strokeWidth = 20f
        strokeCap = Paint.Cap.ROUND
    }
}

onDraw() — การวาดมุมมอง

override fun onDraw(canvas: Canvas) {
    super.onDraw(canvas)

    val cx = width / 2f
    val cy = height / 2f
    val radius = (minOf(width, height) / 2f) - 30f

    // Draw background circle
    canvas.drawCircle(cx, cy, radius, backgroundPaint)

    // Draw progress arc
    val oval = RectF(cx - radius, cy - radius, cx + radius, cy + radius)
    val sweepAngle = 360f * (progress / 100f)
    canvas.drawArc(oval, -90f, sweepAngle, false, progressPaint)
}

invalidate() กับ requestLayout()

แอตทริบิวต์ที่กำหนดเอง (attrs.xml)

<!-- res/values/attrs.xml -->
<resources>
    <declare-styleable name="CircleProgressView">
        <attr name="progressColor" format="color" />
        <attr name="trackColor"    format="color" />
        <attr name="strokeWidth"   format="dimension" />
        <attr name="progress"      format="float" />
    </declare-styleable>
</resources>

การอ่านแอตทริบิวต์ที่กำหนดเอง

init {
    context.obtainStyledAttributes(attrs, R.styleable.CircleProgressView).use { ta ->
        progressPaint.color = ta.getColor(
            R.styleable.CircleProgressView_progressColor,
            Color.parseColor("#6750A4")
        )
        backgroundPaint.color = ta.getColor(
            R.styleable.CircleProgressView_trackColor,
            Color.LTGRAY
        )
        val sw = ta.getDimension(R.styleable.CircleProgressView_strokeWidth, 20f)
        progressPaint.strokeWidth = sw
        backgroundPaint.strokeWidth = sw
        progress = ta.getFloat(R.styleable.CircleProgressView_progress, 0f)
    }
}

การใช้มุมมองที่กำหนดเองใน XML

<!-- In any layout XML -->
<com.example.myapp.CircleProgressView
    android:id="@+id/progressView"
    android:layout_width="120dp"
    android:layout_height="120dp"
    app:progress="65"
    app:progressColor="@color/primary"
    app:trackColor="@color/surface_variant"
    app:strokeWidth="12dp" />

<!-- Control in code: -->
binding.progressView.progress = 75f

มุมมองแบบผสม

class SearchBarView @JvmOverloads constructor(
    context: Context, attrs: AttributeSet? = null
) : LinearLayout(context, attrs) {

    private val binding = ViewSearchBarBinding.inflate(LayoutInflater.from(context), this)

    init {
        orientation = HORIZONTAL
        binding.ivSearch.setOnClickListener {
            onSearchClick?.invoke(binding.etSearch.text.toString())
        }
    }

    var onSearchClick: ((String) -> Unit)? = null

    fun setHint(hint: String) { binding.etSearch.hint = hint }
}

การวาดข้อความ

private val textPaint = Paint(Paint.ANTI_ALIAS_FLAG).apply {
    color = Color.BLACK
    textSize = 48f
    textAlign = Paint.Align.CENTER
}

override fun onDraw(canvas: Canvas) {
    super.onDraw(canvas)
    val cx = width / 2f
    val cy = height / 2f

    // Vertically center the text:
    val fm = textPaint.fontMetrics
    val textY = cy - (fm.ascent + fm.descent) / 2f
    canvas.drawText("${progress.toInt()}%", cx, textY, textPaint)
}

ตรวจสอบความเข้าใจอย่างรวดเร็ว

ทบทวน: มุมมองที่กำหนดเอง