Java tutorial
package com.emmaguy.todayilearned; /* * Copyright 2014 Google Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ import android.content.Context; import android.graphics.Bitmap; import android.graphics.Canvas; import android.graphics.Paint; import android.os.Handler; import android.os.Parcel; import android.os.Parcelable; import android.support.annotation.NonNull; import android.support.v4.os.ParcelableCompat; import android.support.v4.os.ParcelableCompatCreatorCallbacks; import android.util.AttributeSet; import android.util.Log; import android.view.GestureDetector; import android.view.MotionEvent; import android.view.View; import android.widget.EdgeEffect; import android.widget.OverScroller; /** * View which supports panning around an image larger than the screen size. Supports both scrolling * and flinging. From Roman Nurik's Muzei: https://github.com/romannurik/muzei */ public class PanView extends View { private static final String TAG = PanView.class.getSimpleName(); private Bitmap mImage; private Bitmap mScaledImage; private Bitmap mBlurredImage; private float mBlurAmount = 0f; private Paint mDrawBlurredPaint; /** * Horizontal offset for painting the image. As this is used in a canvas.drawBitmap it ranges * from a negative value mWidth-image.getWidth() (remember the view is smaller than the image) * to zero. If it is zero that means the offsetX side of the image is visible otherwise it is * off screen and we are farther to the right. */ private float mOffsetX; /** * Vertical offset for painting the image. As this is used in a canvas.drawBitmap it ranges * from a negative value mHeight-image.getHeight() (remember the view is smaller than the image) * to zero. If it is zero that means the offsetY side of the image is visible otherwise it is * off screen and we are farther down. */ private float mOffsetY; /** * View width */ private int mWidth = 1; /** * View height */ private int mHeight = 1; // State objects and values related to gesture tracking. private GestureDetector mGestureDetector; private OverScroller mScroller; /** * Handler for posting fling animation updates */ private Handler mHandler = new Handler(); // Edge effect / overscroll tracking objects. private EdgeEffect mEdgeEffectTop; private EdgeEffect mEdgeEffectBottom; private EdgeEffect mEdgeEffectLeft; private EdgeEffect mEdgeEffectRight; private boolean mEdgeEffectTopActive; private boolean mEdgeEffectBottomActive; private boolean mEdgeEffectLeftActive; private boolean mEdgeEffectRightActive; private Runnable mAnimateTickRunnable = new Runnable() { @Override public void run() { boolean needsInvalidate = false; if (mScroller.computeScrollOffset()) { // The scroller isn't finished, meaning a fling is currently active. setOffset(mScroller.getCurrX(), mScroller.getCurrY()); if (mWidth != mScaledImage.getWidth() && mOffsetX < mScroller.getCurrX() && mEdgeEffectLeft.isFinished() && !mEdgeEffectLeftActive) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "Left edge absorbing " + mScroller.getCurrVelocity()); } mEdgeEffectLeft.onAbsorb((int) mScroller.getCurrVelocity()); mEdgeEffectLeftActive = true; } else if (mWidth != mScaledImage.getWidth() && mOffsetX > mScroller.getCurrX() && mEdgeEffectRight.isFinished() && !mEdgeEffectRightActive) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "Right edge absorbing " + mScroller.getCurrVelocity()); } mEdgeEffectRight.onAbsorb((int) mScroller.getCurrVelocity()); mEdgeEffectRightActive = true; } if (mHeight != mScaledImage.getHeight() && mOffsetY < mScroller.getCurrY() && mEdgeEffectTop.isFinished() && !mEdgeEffectTopActive) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "Top edge absorbing " + mScroller.getCurrVelocity()); } mEdgeEffectTop.onAbsorb((int) mScroller.getCurrVelocity()); mEdgeEffectTopActive = true; } else if (mHeight != mScaledImage.getHeight() && mOffsetY > mScroller.getCurrY() && mEdgeEffectBottom.isFinished() && !mEdgeEffectBottomActive) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "Bottom edge absorbing " + mScroller.getCurrVelocity()); } mEdgeEffectBottom.onAbsorb((int) mScroller.getCurrVelocity()); mEdgeEffectBottomActive = true; } if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "Flinging to " + mOffsetX + ", " + mOffsetY); } needsInvalidate = true; } if (needsInvalidate) { invalidate(); postAnimateTick(); } } }; public PanView(Context context) { this(context, null, 0); } public PanView(Context context, AttributeSet attrs) { this(context, attrs, 0); } public PanView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); // Sets up interactions mGestureDetector = new GestureDetector(context, new ScrollFlingGestureListener()); mScroller = new OverScroller(context); mEdgeEffectLeft = new EdgeEffect(context); mEdgeEffectTop = new EdgeEffect(context); mEdgeEffectRight = new EdgeEffect(context); mEdgeEffectBottom = new EdgeEffect(context); mDrawBlurredPaint = new Paint(); mDrawBlurredPaint.setDither(true); } /** * Sets an image to be displayed. Preferably this image should be larger than this view's size * to allow scrolling. Note that the image will be centered on first display * * @param image Image to display */ public void setImage(Bitmap image) { mImage = image; updateScaledImage(); } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); mWidth = Math.max(1, w); mHeight = Math.max(1, h); updateScaledImage(); } private void updateScaledImage() { if (mImage == null) { return; } int width = mImage.getWidth(); int height = mImage.getHeight(); if (width > height) { float scalingFactor = mHeight * 1f / height; mScaledImage = Bitmap.createScaledBitmap(mImage, (int) (scalingFactor * width), mHeight, true); } else { float scalingFactor = mWidth * 1f / width; mScaledImage = Bitmap.createScaledBitmap(mImage, mWidth, (int) (scalingFactor * height), true); } // Center the image mOffsetX = (mWidth - mScaledImage.getWidth()) / 2; mOffsetY = (mHeight - mScaledImage.getHeight()) / 2; invalidate(); } @Override protected void onDraw(Canvas canvas) { if (mBlurAmount < 1f) { if (mScaledImage != null) { canvas.drawBitmap(mScaledImage, mOffsetX, mOffsetY, null); } } if (mBlurAmount > 0f) { if (mBlurredImage != null) { mDrawBlurredPaint.setAlpha((int) (mBlurAmount * 255)); canvas.drawBitmap(mBlurredImage, mOffsetX, mOffsetY, mDrawBlurredPaint); } } drawEdgeEffects(canvas); } //////////////////////////////////////////////////////////////////////////////////////////////// // // Methods and objects related to gesture handling // //////////////////////////////////////////////////////////////////////////////////////////////// /** * Draws the overscroll "glow" at the four edges, if necessary * * @see EdgeEffect */ private void drawEdgeEffects(Canvas canvas) { // The methods below rotate and translate the canvas as needed before drawing the glow, // since EdgeEffect always draws a top-glow at 0,0. boolean needsInvalidate = false; if (!mEdgeEffectTop.isFinished()) { final int restoreCount = canvas.save(); mEdgeEffectTop.setSize(mWidth, mHeight); if (mEdgeEffectTop.draw(canvas)) { needsInvalidate = true; } canvas.restoreToCount(restoreCount); } if (!mEdgeEffectBottom.isFinished()) { final int restoreCount = canvas.save(); canvas.translate(-mWidth, mHeight); canvas.rotate(180, mWidth, 0); mEdgeEffectBottom.setSize(mWidth, mHeight); if (mEdgeEffectBottom.draw(canvas)) { needsInvalidate = true; } canvas.restoreToCount(restoreCount); } if (!mEdgeEffectLeft.isFinished()) { final int restoreCount = canvas.save(); canvas.translate(0, mHeight); canvas.rotate(-90, 0, 0); //noinspection SuspiciousNameCombination mEdgeEffectLeft.setSize(mHeight, mWidth); if (mEdgeEffectLeft.draw(canvas)) { needsInvalidate = true; } canvas.restoreToCount(restoreCount); } if (!mEdgeEffectRight.isFinished()) { final int restoreCount = canvas.save(); canvas.translate(mWidth, 0); canvas.rotate(90, 0, 0); //noinspection SuspiciousNameCombination mEdgeEffectRight.setSize(mHeight, mWidth); if (mEdgeEffectRight.draw(canvas)) { needsInvalidate = true; } canvas.restoreToCount(restoreCount); } if (needsInvalidate) { invalidate(); } } @Override public boolean onTouchEvent(@NonNull MotionEvent event) { return mGestureDetector.onTouchEvent(event) || super.onTouchEvent(event); } private void setOffset(float offsetX, float offsetY) { if (mScaledImage == null) { return; } // Constrain between mWidth - mScaledImage.getWidth() and 0 // mWidth - mScaledImage.getWidth() -> right edge visible // 0 -> left edge visible mOffsetX = Math.min(0, Math.max(mWidth - mScaledImage.getWidth(), offsetX)); // Constrain between mHeight - mScaledImage.getHeight() and 0 // mHeight - mScaledImage.getHeight() -> bottom edge visible // 0 -> top edge visible mOffsetY = Math.min(0, Math.max(mHeight - mScaledImage.getHeight(), offsetY)); } private void postAnimateTick() { mHandler.removeCallbacks(mAnimateTickRunnable); mHandler.post(mAnimateTickRunnable); } @Override public Parcelable onSaveInstanceState() { Parcelable superState = super.onSaveInstanceState(); SavedState ss = new SavedState(superState); ss.offsetX = mOffsetX; ss.offsetY = mOffsetY; return ss; } //////////////////////////////////////////////////////////////////////////////////////////////// // // Methods and classes related to view state persistence. // //////////////////////////////////////////////////////////////////////////////////////////////// @Override public void onRestoreInstanceState(Parcelable state) { if (!(state instanceof SavedState)) { super.onRestoreInstanceState(state); return; } SavedState ss = (SavedState) state; super.onRestoreInstanceState(ss.getSuperState()); mOffsetX = ss.offsetX; mOffsetY = ss.offsetY; } /** * Persistent state that is saved by PanView. */ public static class SavedState extends BaseSavedState { public static final Creator<SavedState> CREATOR = ParcelableCompat .newCreator(new ParcelableCompatCreatorCallbacks<SavedState>() { @Override public SavedState createFromParcel(Parcel in, ClassLoader loader) { return new SavedState(in); } @Override public SavedState[] newArray(int size) { return new SavedState[size]; } }); private float offsetX; private float offsetY; public SavedState(Parcelable superState) { super(superState); } SavedState(Parcel in) { super(in); offsetX = in.readFloat(); offsetY = in.readFloat(); } @Override public void writeToParcel(@NonNull Parcel out, int flags) { super.writeToParcel(out, flags); out.writeFloat(offsetX); out.writeFloat(offsetY); } @Override public String toString() { return "PanView.SavedState{" + Integer.toHexString(System.identityHashCode(this)) + " offset=" + offsetX + ", " + offsetY + "}"; } } /** * The gesture listener, used for handling simple gestures such as scrolls and flings. */ private class ScrollFlingGestureListener extends GestureDetector.SimpleOnGestureListener { @Override public boolean onDown(MotionEvent e) { releaseEdgeEffects(); mScroller.forceFinished(true); invalidate(); return true; } @Override public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) { if (mScaledImage == null) { return true; } float offsetX = mOffsetX; float offsetY = mOffsetY; setOffset(mOffsetX - distanceX, mOffsetY - distanceY); if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "Scrolling to " + mOffsetX + ", " + mOffsetY); } if (mWidth != mScaledImage.getWidth() && mOffsetX < offsetX - distanceX) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "Left edge pulled " + -distanceX); } mEdgeEffectLeft.onPull(-distanceX * 1f / mWidth); mEdgeEffectLeftActive = true; } if (mHeight != mScaledImage.getHeight() && mOffsetY < offsetY - distanceY) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "Top edge pulled " + distanceY); } mEdgeEffectTop.onPull(-distanceY * 1f / mHeight); mEdgeEffectTopActive = true; } if (mHeight != mScaledImage.getHeight() && mOffsetY > offsetY - distanceY) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "Bottom edge pulled " + -distanceY); } mEdgeEffectBottom.onPull(distanceY * 1f / mHeight); mEdgeEffectBottomActive = true; } if (mWidth != mScaledImage.getWidth() && mOffsetX > offsetX - distanceX) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "Right edge pulled " + distanceX); } mEdgeEffectRight.onPull(distanceX * 1f / mWidth); mEdgeEffectRightActive = true; } invalidate(); return true; } @Override public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) { if (mScaledImage == null) { return true; } releaseEdgeEffects(); mScroller.forceFinished(true); mScroller.fling((int) mOffsetX, (int) mOffsetY, (int) velocityX, (int) velocityY, mWidth - mScaledImage.getWidth(), 0, // mWidth - mScaledImage.getWidth() is negative mHeight - mScaledImage.getHeight(), 0, // mHeight - mScaledImage.getHeight() is negative mScaledImage.getWidth() / 2, mScaledImage.getHeight() / 2); postAnimateTick(); invalidate(); return true; } private void releaseEdgeEffects() { mEdgeEffectLeftActive = mEdgeEffectTopActive = mEdgeEffectRightActive = mEdgeEffectBottomActive = false; mEdgeEffectLeft.onRelease(); mEdgeEffectTop.onRelease(); mEdgeEffectRight.onRelease(); mEdgeEffectBottom.onRelease(); } } }