Dokumen ini menjelaskan cara menggunakan gestur sentuh untuk menarik dan menskalakan di layar
objek, menggunakan
onTouchEvent()
untuk mencegat peristiwa sentuh.
Menarik objek
Operasi umum untuk gestur sentuh adalah menggunakannya untuk menarik objek layar.
Dalam operasi seret atau scroll, aplikasi harus melacak yang asli meskipun jari lainnya menyentuh layar. Misalnya, bayangkan bahwa sambil menyeret gambar, pengguna meletakkan jari kedua di layar sentuh dan mengangkat jari pertama. Jika aplikasi Anda hanya melacak setiap pointer, aplikasi menganggap pointer kedua sebagai default dan memindahkan gambar ke lokasi HTTP/HTTPS.
Untuk mencegah hal ini terjadi, aplikasi Anda harus membedakan antara
pointer asli dan pointer berikutnya. Untuk melakukannya, ia melacak
ACTION_POINTER_DOWN
dan
ACTION_POINTER_UP
peristiwa seperti yang dijelaskan dalam Menangani gestur multi-kontrol.
ACTION_POINTER_DOWN
dan ACTION_POINTER_UP
berhasil
ke callback onTouchEvent()
setiap kali pointer sekunder berjalan
ke bawah atau ke atas.
Dalam kasus ACTION_POINTER_UP
, Anda dapat mengekstrak indeks ini dan
memastikan bahwa ID pointer aktif tidak merujuk ke pointer yang tidak lagi
menyentuh layar. Jika tersedia, Anda dapat memilih pointer lain untuk diaktifkan
dan simpan posisi
X dan Y saat ini. Gunakan posisi tersimpan ini di
ACTION_MOVE
untuk menghitung jarak guna memindahkan objek pada layar. Dengan cara ini, aplikasi
selalu menghitung jarak untuk bergerak menggunakan data dari {i>pointer<i} yang benar.
Cuplikan kode berikut memungkinkan pengguna menarik objek pada layar. Ini mencatat posisi awal pointer aktif, menghitung jarak bergerak, dan memindahkan objek ke posisi baru. Hal ini juga sesuai akan mengelola kemungkinan adanya pointer tambahan.
Cuplikan tersebut menggunakan atribut
getActionMasked()
. Selalu gunakan metode ini untuk mengambil tindakan suatu
MotionEvent
.
Kotlin
// The "active pointer" is the one moving the object. private var mActivePointerId = INVALID_POINTER_ID override fun onTouchEvent(ev: MotionEvent): Boolean { // Let the ScaleGestureDetector inspect all events. mScaleDetector.onTouchEvent(ev) val action = MotionEventCompat.getActionMasked(ev) when (action) { MotionEvent.ACTION_DOWN -> { MotionEventCompat.getActionIndex(ev).also { pointerIndex -> // Remember where you start for dragging. mLastTouchX = MotionEventCompat.getX(ev, pointerIndex) mLastTouchY = MotionEventCompat.getY(ev, pointerIndex) } // Save the ID of this pointer for dragging. mActivePointerId = MotionEventCompat.getPointerId(ev, 0) } MotionEvent.ACTION_MOVE -> { // Find the index of the active pointer and fetch its position. val (x: Float, y: Float) = MotionEventCompat.findPointerIndex(ev, mActivePointerId).let { pointerIndex -> // Calculate the distance moved. MotionEventCompat.getX(ev, pointerIndex) to MotionEventCompat.getY(ev, pointerIndex) } mPosX += x - mLastTouchX mPosY += y - mLastTouchY invalidate() // Remember this touch position for the next move event. mLastTouchX = x mLastTouchY = y } MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> { mActivePointerId = INVALID_POINTER_ID } MotionEvent.ACTION_POINTER_UP -> { MotionEventCompat.getActionIndex(ev).also { pointerIndex -> MotionEventCompat.getPointerId(ev, pointerIndex) .takeIf { it == mActivePointerId } ?.run { // This is the active pointer going up. Choose a new // active pointer and adjust it accordingly. val newPointerIndex = if (pointerIndex == 0) 1 else 0 mLastTouchX = MotionEventCompat.getX(ev, newPointerIndex) mLastTouchY = MotionEventCompat.getY(ev, newPointerIndex) mActivePointerId = MotionEventCompat.getPointerId(ev, newPointerIndex) } } } } return true }
Java
// The "active pointer" is the one moving the object. private int mActivePointerId = INVALID_POINTER_ID; @Override public boolean onTouchEvent(MotionEvent ev) { // Let the ScaleGestureDetector inspect all events. mScaleDetector.onTouchEvent(ev); final int action = MotionEventCompat.getActionMasked(ev); switch (action) { case MotionEvent.ACTION_DOWN: { final int pointerIndex = MotionEventCompat.getActionIndex(ev); final float x = MotionEventCompat.getX(ev, pointerIndex); final float y = MotionEventCompat.getY(ev, pointerIndex); // Remember the starting position of the pointer. mLastTouchX = x; mLastTouchY = y; // Save the ID of this pointer for dragging. mActivePointerId = MotionEventCompat.getPointerId(ev, 0); break; } case MotionEvent.ACTION_MOVE: { // Find the index of the active pointer and fetch its position. final int pointerIndex = MotionEventCompat.findPointerIndex(ev, mActivePointerId); final float x = MotionEventCompat.getX(ev, pointerIndex); final float y = MotionEventCompat.getY(ev, pointerIndex); // Calculate the distance moved. final float dx = x - mLastTouchX; final float dy = y - mLastTouchY; mPosX += dx; mPosY += dy; invalidate(); // Remember this touch position for the next move event. mLastTouchX = x; mLastTouchY = y; break; } case MotionEvent.ACTION_UP: { mActivePointerId = INVALID_POINTER_ID; break; } case MotionEvent.ACTION_CANCEL: { mActivePointerId = INVALID_POINTER_ID; break; } case MotionEvent.ACTION_POINTER_UP: { final int pointerIndex = MotionEventCompat.getActionIndex(ev); final int pointerId = MotionEventCompat.getPointerId(ev, pointerIndex); if (pointerId == mActivePointerId) { // This is the active pointer going up. Choose a new // active pointer and adjust it accordingly. final int newPointerIndex = pointerIndex == 0 ? 1 : 0; mLastTouchX = MotionEventCompat.getX(ev, newPointerIndex); mLastTouchY = MotionEventCompat.getY(ev, newPointerIndex); mActivePointerId = MotionEventCompat.getPointerId(ev, newPointerIndex); } break; } } return true; }
Tarik untuk menggeser
Bagian sebelumnya menunjukkan contoh penarikan objek pada layar.
Skenario umum lainnya adalah {i>panning<i}, yaitu ketika pengguna menarik {i>motion<i}
menyebabkan pengguliran pada sumbu X dan Y. Cuplikan sebelumnya secara langsung
mencegat tindakan MotionEvent
untuk menerapkan penarikan. Tujuan
di bagian ini memanfaatkan dukungan bawaan platform untuk
{i>gesture <i}umum dengan mengabaikan
onScroll()
inci
GestureDetector.SimpleOnGestureListener
.
Untuk memberikan lebih banyak konteks, onScroll()
dipanggil saat pengguna menarik
jari untuk menggeser konten. onScroll()
hanya dipanggil saat
jari turun. Segera setelah jari diangkat dari layar,
baik berakhir atau gestur ayunkan dimulai, jika jari bergerak dengan
kecepatan sebelum diangkat. Untuk informasi selengkapnya
tentang {i>scrolling<i} vs
ayunkan jari, lihat Menganimasikan gestur scroll.
Berikut adalah cuplikan kode untuk onScroll()
:
Kotlin
// The current viewport. This rectangle represents the visible // chart domain and range. private val mCurrentViewport = RectF(AXIS_X_MIN, AXIS_Y_MIN, AXIS_X_MAX, AXIS_Y_MAX) // The current destination rectangle, in pixel coordinates, into which the // chart data must be drawn. private val mContentRect: Rect? = null private val mGestureListener = object : GestureDetector.SimpleOnGestureListener() { ... override fun onScroll( e1: MotionEvent, e2: MotionEvent, distanceX: Float, distanceY: Float ): Boolean { // Scrolling uses math based on the viewport, as opposed to math using // pixels. mContentRect?.apply { // Pixel offset is the offset in screen pixels, while viewport offset is the // offset within the current viewport. val viewportOffsetX = distanceX * mCurrentViewport.width() / width() val viewportOffsetY = -distanceY * mCurrentViewport.height() / height() // Updates the viewport and refreshes the display. setViewportBottomLeft( mCurrentViewport.left + viewportOffsetX, mCurrentViewport.bottom + viewportOffsetY ) } return true } }
Java
// The current viewport. This rectangle represents the visible // chart domain and range. private RectF mCurrentViewport = new RectF(AXIS_X_MIN, AXIS_Y_MIN, AXIS_X_MAX, AXIS_Y_MAX); // The current destination rectangle, in pixel coordinates, into which the // chart data must be drawn. private Rect mContentRect; private final GestureDetector.SimpleOnGestureListener mGestureListener = new GestureDetector.SimpleOnGestureListener() { ... @Override public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) { // Scrolling uses math based on the viewport, as opposed to math using // pixels. // Pixel offset is the offset in screen pixels, while viewport offset is the // offset within the current viewport. float viewportOffsetX = distanceX * mCurrentViewport.width() / mContentRect.width(); float viewportOffsetY = -distanceY * mCurrentViewport.height() / mContentRect.height(); ... // Updates the viewport, refreshes the display. setViewportBottomLeft( mCurrentViewport.left + viewportOffsetX, mCurrentViewport.bottom + viewportOffsetY); ... return true; }
Implementasi onScroll()
men-scroll area tampilan di
terhadap gestur sentuh:
Kotlin
/** * Sets the current viewport, defined by mCurrentViewport, to the given * X and Y positions. The Y value represents the topmost pixel position, * and thus the bottom of the mCurrentViewport rectangle. */ private fun setViewportBottomLeft(x: Float, y: Float) { /* * Constrains within the scroll range. The scroll range is the viewport * extremes, such as AXIS_X_MAX, minus the viewport size. For example, if * the extremes are 0 and 10 and the viewport size is 2, the scroll range * is 0 to 8. */ val curWidth: Float = mCurrentViewport.width() val curHeight: Float = mCurrentViewport.height() val newX: Float = Math.max(AXIS_X_MIN, Math.min(x, AXIS_X_MAX - curWidth)) val newY: Float = Math.max(AXIS_Y_MIN + curHeight, Math.min(y, AXIS_Y_MAX)) mCurrentViewport.set(newX, newY - curHeight, newX + curWidth, newY) // Invalidates the View to update the display. ViewCompat.postInvalidateOnAnimation(this) }
Java
/** * Sets the current viewport (defined by mCurrentViewport) to the given * X and Y positions. Note that the Y value represents the topmost pixel * position, and thus the bottom of the mCurrentViewport rectangle. */ private void setViewportBottomLeft(float x, float y) { /* * Constrains within the scroll range. The scroll range is the viewport * extremes, such as AXIS_X_MAX, minus the viewport size. For example, if * the extremes are 0 and 10 and the viewport size is 2, the scroll range * is 0 to 8. */ float curWidth = mCurrentViewport.width(); float curHeight = mCurrentViewport.height(); x = Math.max(AXIS_X_MIN, Math.min(x, AXIS_X_MAX - curWidth)); y = Math.max(AXIS_Y_MIN + curHeight, Math.min(y, AXIS_Y_MAX)); mCurrentViewport.set(x, y - curHeight, x + curWidth, y); // Invalidates the View to update the display. ViewCompat.postInvalidateOnAnimation(this); }
Menggunakan sentuhan untuk melakukan penskalaan
Seperti yang telah dibahas dalam Mendeteksi gestur umum,
penggunaan
GestureDetector
untuk mendeteksi {i>gesture <i}umum yang digunakan oleh Android, seperti menggulir, mengayunkan jari, dan
sentuh lama. Untuk penskalaan, Android menyediakan
ScaleGestureDetector
.
Anda dapat menggunakan GestureDetector
dan ScaleGestureDetector
secara bersamaan bila Anda ingin tampilan mengenali {i>gesture <i}tambahan.
Untuk melaporkan peristiwa gestur yang terdeteksi, pendeteksi gestur menggunakan objek pemroses
diteruskan ke konstruktornya. ScaleGestureDetector
penggunaan
ScaleGestureDetector.OnScaleGestureListener
.
Android menyediakan
ScaleGestureDetector.SimpleOnScaleGestureListener
sebagai class bantuan yang dapat diperluas jika Anda tidak memerlukan
peristiwa.
Contoh penskalaan dasar
Cuplikan berikut mengilustrasikan elemen dasar yang terlibat dalam penskalaan.
Kotlin
private var mScaleFactor = 1f private val scaleListener = object : ScaleGestureDetector.SimpleOnScaleGestureListener() { override fun onScale(detector: ScaleGestureDetector): Boolean { mScaleFactor *= detector.scaleFactor // Don't let the object get too small or too large. mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 5.0f)) invalidate() return true } } private val mScaleDetector = ScaleGestureDetector(context, scaleListener) override fun onTouchEvent(ev: MotionEvent): Boolean { // Let the ScaleGestureDetector inspect all events. mScaleDetector.onTouchEvent(ev) return true } override fun onDraw(canvas: Canvas?) { super.onDraw(canvas) canvas?.apply { save() scale(mScaleFactor, mScaleFactor) // onDraw() code goes here. restore() } }
Java
private ScaleGestureDetector mScaleDetector; private float mScaleFactor = 1.f; public MyCustomView(Context mContext){ ... // View code goes here. ... mScaleDetector = new ScaleGestureDetector(context, new ScaleListener()); } @Override public boolean onTouchEvent(MotionEvent ev) { // Let the ScaleGestureDetector inspect all events. mScaleDetector.onTouchEvent(ev); return true; } @Override public void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.save(); canvas.scale(mScaleFactor, mScaleFactor); ... // onDraw() code goes here. ... canvas.restore(); } private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener { @Override public boolean onScale(ScaleGestureDetector detector) { mScaleFactor *= detector.getScaleFactor(); // Don't let the object get too small or too large. mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 5.0f)); invalidate(); return true; } }
Contoh penskalaan yang lebih kompleks
Berikut ini adalah contoh yang lebih kompleks dari
InteractiveChart
sampel ditampilkan di
Menganimasikan gestur scroll.
Tujuan
Contoh InteractiveChart
mendukung scroll, penggeseran, dan penskalaan
dengan beberapa jari, menggunakan rentang ScaleGestureDetector
(getCurrentSpanX
)
dan
getCurrentSpanY
)
dan "fokus"
(getFocusX
dan getFocusY
)
baru.
Kotlin
private val mCurrentViewport = RectF(AXIS_X_MIN, AXIS_Y_MIN, AXIS_X_MAX, AXIS_Y_MAX) private val mContentRect: Rect? = null ... override fun onTouchEvent(event: MotionEvent): Boolean { return mScaleGestureDetector.onTouchEvent(event) || mGestureDetector.onTouchEvent(event) || super.onTouchEvent(event) } /** * The scale listener, used for handling multi-finger scale gestures. */ private val mScaleGestureListener = object : ScaleGestureDetector.SimpleOnScaleGestureListener() { /** * This is the active focal point in terms of the viewport. It can be a * local variable, but keep it here to minimize per-frame allocations. */ private val viewportFocus = PointF() private var lastSpanX: Float = 0f private var lastSpanY: Float = 0f // Detects new pointers are going down. override fun onScaleBegin(scaleGestureDetector: ScaleGestureDetector): Boolean { lastSpanX = scaleGestureDetector.currentSpanX lastSpanY = scaleGestureDetector.currentSpanY return true } override fun onScale(scaleGestureDetector: ScaleGestureDetector): Boolean { val spanX: Float = scaleGestureDetector.currentSpanX val spanY: Float = scaleGestureDetector.currentSpanY val newWidth: Float = lastSpanX / spanX * mCurrentViewport.width() val newHeight: Float = lastSpanY / spanY * mCurrentViewport.height() val focusX: Float = scaleGestureDetector.focusX val focusY: Float = scaleGestureDetector.focusY // Ensures the chart point is within the chart region. // See the sample for the implementation of hitTest(). hitTest(focusX, focusY, viewportFocus) mContentRect?.apply { mCurrentViewport.set( viewportFocus.x - newWidth * (focusX - left) / width(), viewportFocus.y - newHeight * (bottom - focusY) / height(), 0f, 0f ) } mCurrentViewport.right = mCurrentViewport.left + newWidth mCurrentViewport.bottom = mCurrentViewport.top + newHeight // Invalidates the View to update the display. ViewCompat.postInvalidateOnAnimation(this@InteractiveLineGraphView) lastSpanX = spanX lastSpanY = spanY return true } }
Java
private RectF mCurrentViewport = new RectF(AXIS_X_MIN, AXIS_Y_MIN, AXIS_X_MAX, AXIS_Y_MAX); private Rect mContentRect; private ScaleGestureDetector mScaleGestureDetector; ... @Override public boolean onTouchEvent(MotionEvent event) { boolean retVal = mScaleGestureDetector.onTouchEvent(event); retVal = mGestureDetector.onTouchEvent(event) || retVal; return retVal || super.onTouchEvent(event); } /** * The scale listener, used for handling multi-finger scale gestures. */ private final ScaleGestureDetector.OnScaleGestureListener mScaleGestureListener = new ScaleGestureDetector.SimpleOnScaleGestureListener() { /** * This is the active focal point in terms of the viewport. It can be a * local variable, but keep it here to minimize per-frame allocations. */ private PointF viewportFocus = new PointF(); private float lastSpanX; private float lastSpanY; // Detects new pointers are going down. @Override public boolean onScaleBegin(ScaleGestureDetector scaleGestureDetector) { lastSpanX = ScaleGestureDetectorCompat. getCurrentSpanX(scaleGestureDetector); lastSpanY = ScaleGestureDetectorCompat. getCurrentSpanY(scaleGestureDetector); return true; } @Override public boolean onScale(ScaleGestureDetector scaleGestureDetector) { float spanX = ScaleGestureDetectorCompat. getCurrentSpanX(scaleGestureDetector); float spanY = ScaleGestureDetectorCompat. getCurrentSpanY(scaleGestureDetector); float newWidth = lastSpanX / spanX * mCurrentViewport.width(); float newHeight = lastSpanY / spanY * mCurrentViewport.height(); float focusX = scaleGestureDetector.getFocusX(); float focusY = scaleGestureDetector.getFocusY(); // Ensures the chart point is within the chart region. // See the sample for the implementation of hitTest(). hitTest(scaleGestureDetector.getFocusX(), scaleGestureDetector.getFocusY(), viewportFocus); mCurrentViewport.set( viewportFocus.x - newWidth * (focusX - mContentRect.left) / mContentRect.width(), viewportFocus.y - newHeight * (mContentRect.bottom - focusY) / mContentRect.height(), 0, 0); mCurrentViewport.right = mCurrentViewport.left + newWidth; mCurrentViewport.bottom = mCurrentViewport.top + newHeight; ... // Invalidates the View to update the display. ViewCompat.postInvalidateOnAnimation(InteractiveLineGraphView.this); lastSpanX = spanX; lastSpanY = spanY; return true; } };
Referensi lainnya
Lihat referensi berikut untuk informasi selengkapnya tentang peristiwa input, sensor, dan membuat tampilan kustom menjadi interaktif.