Java tutorial
/* * Copyright 2015 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. */ package com.bluelinelabs.conductor.demo.widget; import android.content.Context; import android.support.v4.view.NestedScrollingParent; import android.support.v4.view.animation.FastOutSlowInInterpolator; import android.util.AttributeSet; import android.util.TypedValue; import android.view.View; import android.widget.FrameLayout; import java.util.ArrayList; import java.util.List; /** * A {@link FrameLayout} which responds to nested scrolls to create drag-dismissable layouts. * Applies an elasticity factor to reduce movement as you approach the given dismiss distance. * Optionally also scales down content during drag. */ public class ElasticDragDismissFrameLayout extends FrameLayout implements NestedScrollingParent { public static abstract class ElasticDragDismissCallback { /** * Called for each drag event. * * @param elasticOffset Indicating the drag offset with elasticity applied i.e. may * exceed 1. * @param elasticOffsetPixels The elastically scaled drag distance in pixels. * @param rawOffset Value from [0, 1] indicating the raw drag offset i.e. * without elasticity applied. A value of 1 indicates that the * dismiss distance has been reached. * @param rawOffsetPixels The raw distance the user has dragged */ public void onDrag(float elasticOffset, float elasticOffsetPixels, float rawOffset, float rawOffsetPixels) { } /** * Called when dragging is released and has exceeded the threshold dismiss distance. */ public void onDragDismissed() { } } // configurable attribs private float dragDismissDistance = Float.MAX_VALUE; private float dragDismissFraction = -1f; private float dragDismissScale = 1f; private boolean shouldScale = false; private float dragElacticity = 0.8f; // state private float totalDrag; private boolean draggingDown = false; private boolean draggingUp = false; private List<ElasticDragDismissCallback> callbacks; public ElasticDragDismissFrameLayout(Context context) { this(context, null, 0); } public ElasticDragDismissFrameLayout(Context context, AttributeSet attrs) { this(context, attrs, 0); } public ElasticDragDismissFrameLayout(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); dragDismissDistance = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 80, getResources().getDisplayMetrics()); dragDismissFraction = 0.7f; dragDismissScale = 0.8f; shouldScale = true; } @Override public boolean onStartNestedScroll(View child, View target, int nestedScrollAxes) { return (nestedScrollAxes & View.SCROLL_AXIS_VERTICAL) != 0; } @Override public void onNestedPreScroll(View target, int dx, int dy, int[] consumed) { // if we're in a drag gesture and the user reverses up the we should take those events if (draggingDown && dy > 0 || draggingUp && dy < 0) { dragScale(dy); consumed[1] = dy; } } @Override public void onNestedScroll(View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed) { dragScale(dyUnconsumed); } @Override public void onStopNestedScroll(View child) { if (Math.abs(totalDrag) >= dragDismissDistance) { dispatchDismissCallback(); } else { // settle back to natural position animate().translationY(0f).scaleX(1f).scaleY(1f).setDuration(200L) .setInterpolator(new FastOutSlowInInterpolator()).setListener(null).start(); totalDrag = 0; draggingDown = draggingUp = false; dispatchDragCallback(0f, 0f, 0f, 0f); } } @Override public boolean onNestedFling(View target, float velocityX, float velocityY, boolean consumed) { return false; } @Override public boolean onNestedPreFling(View target, float velocityX, float velocityY) { return false; } @Override public int getNestedScrollAxes() { return 0; } @Override public void onNestedScrollAccepted(View child, View target, int axes) { } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); if (dragDismissFraction > 0f) { dragDismissDistance = h * dragDismissFraction; } } public void addListener(ElasticDragDismissCallback listener) { if (callbacks == null) { callbacks = new ArrayList<>(); } callbacks.add(listener); } public void removeListener(ElasticDragDismissCallback listener) { if (callbacks != null && callbacks.size() > 0) { callbacks.remove(listener); } } private void dragScale(int scroll) { if (scroll == 0) return; totalDrag += scroll; // track the direction & set the pivot point for scaling // don't double track i.e. if start dragging down and then reverse, keep tracking as // dragging down until they reach the 'natural' position if (scroll < 0 && !draggingUp && !draggingDown) { draggingDown = true; if (shouldScale) setPivotY(getHeight()); } else if (scroll > 0 && !draggingDown && !draggingUp) { draggingUp = true; if (shouldScale) setPivotY(0f); } setPivotX(getWidth() / 2); // how far have we dragged relative to the distance to perform a dismiss // (01 where 1 = dismiss distance). Decreasing logarithmically as we approach the limit float dragFraction = (float) Math.log10(1 + (Math.abs(totalDrag) / dragDismissDistance)); // calculate the desired translation given the drag fraction float dragTo = dragFraction * dragDismissDistance * dragElacticity; if (draggingUp) { // as we use the absolute magnitude when calculating the drag fraction, need to // re-apply the drag direction dragTo *= -1; } setTranslationY(dragTo); if (shouldScale) { final float scale = 1 - ((1 - dragDismissScale) * dragFraction); setScaleX(scale); setScaleY(scale); } // if we've reversed direction and gone past the settle point then clear the flags to // allow the list to get the scroll events & reset any transforms if ((draggingDown && totalDrag >= 0) || (draggingUp && totalDrag <= 0)) { totalDrag = dragTo = dragFraction = 0; draggingDown = draggingUp = false; setTranslationY(0f); setScaleX(1f); setScaleY(1f); } dispatchDragCallback(dragFraction, dragTo, Math.min(1f, Math.abs(totalDrag) / dragDismissDistance), totalDrag); } private void dispatchDragCallback(float elasticOffset, float elasticOffsetPixels, float rawOffset, float rawOffsetPixels) { if (callbacks != null && !callbacks.isEmpty()) { for (ElasticDragDismissCallback callback : callbacks) { callback.onDrag(elasticOffset, elasticOffsetPixels, rawOffset, rawOffsetPixels); } } } private void dispatchDismissCallback() { if (callbacks != null && !callbacks.isEmpty()) { for (ElasticDragDismissCallback callback : callbacks) { callback.onDragDismissed(); } } } }