CheatSheet.java

/*
 * Copyright 2012 Roman Nurik
 *
 * 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.tfltravelalerts.common;

import android.content.Context;
import android.graphics.Rect;
import android.text.TextUtils;
import android.view.Gravity;
import android.view.View;
import android.widget.Toast;

/**
 * Helper class for showing cheat sheets (tooltips) for icon-only UI elements on
 * long-press. This is already default platform behavior for icon-only
 * {@link android.app.ActionBar} items and tabs. This class provides this
 * behavior for any other such UI element.
 * <p>
 * Based on the original action bar implementation in <a href=
 * "https://android.googlesource.com/platform/frameworks/base/+/refs/heads/master/core/java/com/android/internal/view/menu/ActionMenuItemView.java"
 * > ActionMenuItemView.java</a>.
 */
public class CheatSheet {
    /**
     * The estimated height of a toast, in dips (density-independent pixels).
     * This is used to determine whether or not the toast should appear above or
     * below the UI element.
     */
    private static final int ESTIMATED_TOAST_HEIGHT_DIPS = 48;

    /**
     * Sets up a cheat sheet (tooltip) for the given view by setting its
     * {@link android.view.View.OnLongClickListener}. When the view is
     * long-pressed, a {@link Toast} with the view's
     * {@link android.view.View#getContentDescription() content description}
     * will be shown either above (default) or below the view (if there isn't
     * room above it).
     * 
     * @param view The view to add a cheat sheet for.
     */
    public static void setup(View view) {
        view.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View view) {
                return showCheatSheet(view, view.getContentDescription());
            }
        });
    }

    /**
     * Sets up a cheat sheet (tooltip) for the given view by setting its
     * {@link android.view.View.OnLongClickListener}. When the view is
     * long-pressed, a {@link Toast} with the given text will be shown either
     * above (default) or below the view (if there isn't room above it).
     * 
     * @param view The view to add a cheat sheet for.
     * @param textResId The string resource containing the text to show on
     *            long-press.
     */
    public static void setup(View view, final int textResId) {
        view.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View view) {
                return showCheatSheet(view, view.getContext().getString(textResId));
            }
        });
    }

    /**
     * Sets up a cheat sheet (tooltip) for the given view by setting its
     * {@link android.view.View.OnLongClickListener}. When the view is
     * long-pressed, a {@link Toast} with the given text will be shown either
     * above (default) or below the view (if there isn't room above it).
     * 
     * @param view The view to add a cheat sheet for.
     * @param text The text to show on long-press.
     */
    public static void setup(View view, final CharSequence text) {
        view.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View view) {
                return showCheatSheet(view, text);
            }
        });
    }

    /**
     * Removes the cheat sheet for the given view by removing the view's
     * {@link android.view.View.OnLongClickListener}.
     * 
     * @param view The view whose cheat sheet should be removed.
     */
    public static void remove(final View view) {
        view.setOnLongClickListener(null);
    }

    /**
     * Internal helper method to show the cheat sheet toast.
     */
    private static boolean showCheatSheet(View view, CharSequence text) {
        if (TextUtils.isEmpty(text)) {
            return false;
        }

        final int[] screenPos = new int[2]; // origin is device display
        final Rect displayFrame = new Rect(); // includes decorations (e.g.
                                              // status bar)
        view.getLocationOnScreen(screenPos);
        view.getWindowVisibleDisplayFrame(displayFrame);

        final Context context = view.getContext();
        final int viewWidth = view.getWidth();
        final int viewHeight = view.getHeight();
        final int viewCenterX = screenPos[0] + viewWidth / 2;
        final int screenWidth = context.getResources().getDisplayMetrics().widthPixels;
        final int estimatedToastHeight = (int) (ESTIMATED_TOAST_HEIGHT_DIPS
                * context.getResources().getDisplayMetrics().density);

        Toast cheatSheet = Toast.makeText(context, text, Toast.LENGTH_SHORT);
        boolean showBelow = screenPos[1] < estimatedToastHeight;
        if (showBelow) {
            // Show below
            // Offsets are after decorations (e.g. status bar) are factored in
            cheatSheet.setGravity(Gravity.TOP | Gravity.CENTER_HORIZONTAL,
                    viewCenterX - screenWidth / 2,
                    screenPos[1] - displayFrame.top + viewHeight);
        } else {
            // Show above
            // Offsets are after decorations (e.g. status bar) are factored in
            cheatSheet.setGravity(Gravity.BOTTOM | Gravity.CENTER_HORIZONTAL,
                    viewCenterX - screenWidth / 2,
                    displayFrame.bottom - screenPos[1]);
        }

        cheatSheet.show();
        return true;
    }
}