Java tutorial
/* * Copyright (C) 2006 The Android Open Source Project * * 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 android.support.v4.widget; import android.graphics.Rect; import android.view.View; /** * Standard constants and tools for placing an object within a potentially * larger container. */ public class Gravity { /** Constant indicating that no gravity has been set **/ public static final int NO_GRAVITY = 0x0000; /** Raw bit indicating the gravity for an axis has been specified. */ public static final int AXIS_SPECIFIED = 0x0001; /** Raw bit controlling how the left/top edge is placed. */ public static final int AXIS_PULL_BEFORE = 0x0002; /** Raw bit controlling how the right/bottom edge is placed. */ public static final int AXIS_PULL_AFTER = 0x0004; /** Raw bit controlling whether the right/bottom edge is clipped to its * container, based on the gravity direction being applied. */ public static final int AXIS_CLIP = 0x0008; /** Bits defining the horizontal axis. */ public static final int AXIS_X_SHIFT = 0; /** Bits defining the vertical axis. */ public static final int AXIS_Y_SHIFT = 4; /** Push object to the top of its container, not changing its size. */ public static final int TOP = (AXIS_PULL_BEFORE | AXIS_SPECIFIED) << AXIS_Y_SHIFT; /** Push object to the bottom of its container, not changing its size. */ public static final int BOTTOM = (AXIS_PULL_AFTER | AXIS_SPECIFIED) << AXIS_Y_SHIFT; /** Push object to the left of its container, not changing its size. */ public static final int LEFT = (AXIS_PULL_BEFORE | AXIS_SPECIFIED) << AXIS_X_SHIFT; /** Push object to the right of its container, not changing its size. */ public static final int RIGHT = (AXIS_PULL_AFTER | AXIS_SPECIFIED) << AXIS_X_SHIFT; /** Place object in the vertical center of its container, not changing its * size. */ public static final int CENTER_VERTICAL = AXIS_SPECIFIED << AXIS_Y_SHIFT; /** Grow the vertical size of the object if needed so it completely fills * its container. */ public static final int FILL_VERTICAL = TOP | BOTTOM; /** Place object in the horizontal center of its container, not changing its * size. */ public static final int CENTER_HORIZONTAL = AXIS_SPECIFIED << AXIS_X_SHIFT; /** Grow the horizontal size of the object if needed so it completely fills * its container. */ public static final int FILL_HORIZONTAL = LEFT | RIGHT; /** Place the object in the center of its container in both the vertical * and horizontal axis, not changing its size. */ public static final int CENTER = CENTER_VERTICAL | CENTER_HORIZONTAL; /** Grow the horizontal and vertical size of the object if needed so it * completely fills its container. */ public static final int FILL = FILL_VERTICAL | FILL_HORIZONTAL; /** Flag to clip the edges of the object to its container along the * vertical axis. */ public static final int CLIP_VERTICAL = AXIS_CLIP << AXIS_Y_SHIFT; /** Flag to clip the edges of the object to its container along the * horizontal axis. */ public static final int CLIP_HORIZONTAL = AXIS_CLIP << AXIS_X_SHIFT; /** Raw bit controlling whether the layout direction is relative or not (START/END instead of * absolute LEFT/RIGHT). */ public static final int RELATIVE_LAYOUT_DIRECTION = 0x00800000; /** * Binary mask to get the absolute horizontal gravity of a gravity. */ public static final int HORIZONTAL_GRAVITY_MASK = (AXIS_SPECIFIED | AXIS_PULL_BEFORE | AXIS_PULL_AFTER) << AXIS_X_SHIFT; /** * Binary mask to get the vertical gravity of a gravity. */ public static final int VERTICAL_GRAVITY_MASK = (AXIS_SPECIFIED | AXIS_PULL_BEFORE | AXIS_PULL_AFTER) << AXIS_Y_SHIFT; /** Special constant to enable clipping to an overall display along the * vertical dimension. This is not applied by default by * {@link #apply(int, int, int, Rect, int, int, Rect)}; you must do so * yourself by calling {@link #applyDisplay}. */ public static final int DISPLAY_CLIP_VERTICAL = 0x10000000; /** Special constant to enable clipping to an overall display along the * horizontal dimension. This is not applied by default by * {@link #apply(int, int, int, Rect, int, int, Rect)}; you must do so * yourself by calling {@link #applyDisplay}. */ public static final int DISPLAY_CLIP_HORIZONTAL = 0x01000000; /** Push object to x-axis position at the start of its container, not changing its size. */ public static final int START = RELATIVE_LAYOUT_DIRECTION | LEFT; /** Push object to x-axis position at the end of its container, not changing its size. */ public static final int END = RELATIVE_LAYOUT_DIRECTION | RIGHT; /** * Binary mask for the horizontal gravity and script specific direction bit. */ public static final int RELATIVE_HORIZONTAL_GRAVITY_MASK = START | END; /** * Apply a gravity constant to an object. This suppose that the layout direction is LTR. * * @param gravity The desired placement of the object, as defined by the * constants in this class. * @param w The horizontal size of the object. * @param h The vertical size of the object. * @param container The frame of the containing space, in which the object * will be placed. Should be large enough to contain the * width and height of the object. * @param outRect Receives the computed frame of the object in its * container. */ public static void apply(int gravity, int w, int h, Rect container, Rect outRect) { apply(gravity, w, h, container, 0, 0, outRect); } /** * Apply a gravity constant to an object and take care if layout direction is RTL or not. * * @param gravity The desired placement of the object, as defined by the * constants in this class. * @param w The horizontal size of the object. * @param h The vertical size of the object. * @param container The frame of the containing space, in which the object * will be placed. Should be large enough to contain the * width and height of the object. * @param outRect Receives the computed frame of the object in its * container. * @param layoutDirection The layout direction. * * @see View#LAYOUT_DIRECTION_LTR * @see View#LAYOUT_DIRECTION_RTL */ public static void apply(int gravity, int w, int h, Rect container, Rect outRect, int layoutDirection) { int absGravity = getAbsoluteGravity(gravity, layoutDirection); apply(absGravity, w, h, container, 0, 0, outRect); } /** * Apply a gravity constant to an object. * * @param gravity The desired placement of the object, as defined by the * constants in this class. * @param w The horizontal size of the object. * @param h The vertical size of the object. * @param container The frame of the containing space, in which the object * will be placed. Should be large enough to contain the * width and height of the object. * @param xAdj Offset to apply to the X axis. If gravity is LEFT this * pushes it to the right; if gravity is RIGHT it pushes it to * the left; if gravity is CENTER_HORIZONTAL it pushes it to the * right or left; otherwise it is ignored. * @param yAdj Offset to apply to the Y axis. If gravity is TOP this pushes * it down; if gravity is BOTTOM it pushes it up; if gravity is * CENTER_VERTICAL it pushes it down or up; otherwise it is * ignored. * @param outRect Receives the computed frame of the object in its * container. */ public static void apply(int gravity, int w, int h, Rect container, int xAdj, int yAdj, Rect outRect) { switch (gravity & ((AXIS_PULL_BEFORE | AXIS_PULL_AFTER) << AXIS_X_SHIFT)) { case 0: outRect.left = container.left + ((container.right - container.left - w) / 2) + xAdj; outRect.right = outRect.left + w; if ((gravity & (AXIS_CLIP << AXIS_X_SHIFT)) == (AXIS_CLIP << AXIS_X_SHIFT)) { if (outRect.left < container.left) { outRect.left = container.left; } if (outRect.right > container.right) { outRect.right = container.right; } } break; case AXIS_PULL_BEFORE << AXIS_X_SHIFT: outRect.left = container.left + xAdj; outRect.right = outRect.left + w; if ((gravity & (AXIS_CLIP << AXIS_X_SHIFT)) == (AXIS_CLIP << AXIS_X_SHIFT)) { if (outRect.right > container.right) { outRect.right = container.right; } } break; case AXIS_PULL_AFTER << AXIS_X_SHIFT: outRect.right = container.right - xAdj; outRect.left = outRect.right - w; if ((gravity & (AXIS_CLIP << AXIS_X_SHIFT)) == (AXIS_CLIP << AXIS_X_SHIFT)) { if (outRect.left < container.left) { outRect.left = container.left; } } break; default: outRect.left = container.left + xAdj; outRect.right = container.right + xAdj; break; } switch (gravity & ((AXIS_PULL_BEFORE | AXIS_PULL_AFTER) << AXIS_Y_SHIFT)) { case 0: outRect.top = container.top + ((container.bottom - container.top - h) / 2) + yAdj; outRect.bottom = outRect.top + h; if ((gravity & (AXIS_CLIP << AXIS_Y_SHIFT)) == (AXIS_CLIP << AXIS_Y_SHIFT)) { if (outRect.top < container.top) { outRect.top = container.top; } if (outRect.bottom > container.bottom) { outRect.bottom = container.bottom; } } break; case AXIS_PULL_BEFORE << AXIS_Y_SHIFT: outRect.top = container.top + yAdj; outRect.bottom = outRect.top + h; if ((gravity & (AXIS_CLIP << AXIS_Y_SHIFT)) == (AXIS_CLIP << AXIS_Y_SHIFT)) { if (outRect.bottom > container.bottom) { outRect.bottom = container.bottom; } } break; case AXIS_PULL_AFTER << AXIS_Y_SHIFT: outRect.bottom = container.bottom - yAdj; outRect.top = outRect.bottom - h; if ((gravity & (AXIS_CLIP << AXIS_Y_SHIFT)) == (AXIS_CLIP << AXIS_Y_SHIFT)) { if (outRect.top < container.top) { outRect.top = container.top; } } break; default: outRect.top = container.top + yAdj; outRect.bottom = container.bottom + yAdj; break; } } /** * Apply a gravity constant to an object. * * @param gravity The desired placement of the object, as defined by the * constants in this class. * @param w The horizontal size of the object. * @param h The vertical size of the object. * @param container The frame of the containing space, in which the object * will be placed. Should be large enough to contain the * width and height of the object. * @param xAdj Offset to apply to the X axis. If gravity is LEFT this * pushes it to the right; if gravity is RIGHT it pushes it to * the left; if gravity is CENTER_HORIZONTAL it pushes it to the * right or left; otherwise it is ignored. * @param yAdj Offset to apply to the Y axis. If gravity is TOP this pushes * it down; if gravity is BOTTOM it pushes it up; if gravity is * CENTER_VERTICAL it pushes it down or up; otherwise it is * ignored. * @param outRect Receives the computed frame of the object in its * container. * @param layoutDirection The layout direction. * * @see View#LAYOUT_DIRECTION_LTR * @see View#LAYOUT_DIRECTION_RTL */ public static void apply(int gravity, int w, int h, Rect container, int xAdj, int yAdj, Rect outRect, int layoutDirection) { int absGravity = getAbsoluteGravity(gravity, layoutDirection); apply(absGravity, w, h, container, xAdj, yAdj, outRect); } /** * Apply additional gravity behavior based on the overall "display" that an * object exists in. This can be used after * {@link #apply(int, int, int, Rect, int, int, Rect)} to place the object * within a visible display. By default this moves or clips the object * to be visible in the display; the gravity flags * {@link #DISPLAY_CLIP_HORIZONTAL} and {@link #DISPLAY_CLIP_VERTICAL} * can be used to change this behavior. * * @param gravity Gravity constants to modify the placement within the * display. * @param display The rectangle of the display in which the object is * being placed. * @param inoutObj Supplies the current object position; returns with it * modified if needed to fit in the display. */ public static void applyDisplay(int gravity, Rect display, Rect inoutObj) { if ((gravity & DISPLAY_CLIP_VERTICAL) != 0) { if (inoutObj.top < display.top) inoutObj.top = display.top; if (inoutObj.bottom > display.bottom) inoutObj.bottom = display.bottom; } else { int off = 0; if (inoutObj.top < display.top) off = display.top - inoutObj.top; else if (inoutObj.bottom > display.bottom) off = display.bottom - inoutObj.bottom; if (off != 0) { if (inoutObj.height() > (display.bottom - display.top)) { inoutObj.top = display.top; inoutObj.bottom = display.bottom; } else { inoutObj.top += off; inoutObj.bottom += off; } } } if ((gravity & DISPLAY_CLIP_HORIZONTAL) != 0) { if (inoutObj.left < display.left) inoutObj.left = display.left; if (inoutObj.right > display.right) inoutObj.right = display.right; } else { int off = 0; if (inoutObj.left < display.left) off = display.left - inoutObj.left; else if (inoutObj.right > display.right) off = display.right - inoutObj.right; if (off != 0) { if (inoutObj.width() > (display.right - display.left)) { inoutObj.left = display.left; inoutObj.right = display.right; } else { inoutObj.left += off; inoutObj.right += off; } } } } /** * Apply additional gravity behavior based on the overall "display" that an * object exists in. This can be used after * {@link #apply(int, int, int, Rect, int, int, Rect)} to place the object * within a visible display. By default this moves or clips the object * to be visible in the display; the gravity flags * {@link #DISPLAY_CLIP_HORIZONTAL} and {@link #DISPLAY_CLIP_VERTICAL} * can be used to change this behavior. * * @param gravity Gravity constants to modify the placement within the * display. * @param display The rectangle of the display in which the object is * being placed. * @param inoutObj Supplies the current object position; returns with it * modified if needed to fit in the display. * @param layoutDirection The layout direction. * * @see View#LAYOUT_DIRECTION_LTR * @see View#LAYOUT_DIRECTION_RTL */ public static void applyDisplay(int gravity, Rect display, Rect inoutObj, int layoutDirection) { int absGravity = getAbsoluteGravity(gravity, layoutDirection); applyDisplay(absGravity, display, inoutObj); } /** * <p>Indicate whether the supplied gravity has a vertical pull.</p> * * @param gravity the gravity to check for vertical pull * @return true if the supplied gravity has a vertical pull */ public static boolean isVertical(int gravity) { return gravity > 0 && (gravity & VERTICAL_GRAVITY_MASK) != 0; } /** * <p>Indicate whether the supplied gravity has an horizontal pull.</p> * * @param gravity the gravity to check for horizontal pull * @return true if the supplied gravity has an horizontal pull */ public static boolean isHorizontal(int gravity) { return gravity > 0 && (gravity & RELATIVE_HORIZONTAL_GRAVITY_MASK) != 0; } /** * <p>Convert script specific gravity to absolute horizontal value.</p> * * if horizontal direction is LTR, then START will set LEFT and END will set RIGHT. * if horizontal direction is RTL, then START will set RIGHT and END will set LEFT. * * * @param gravity The gravity to convert to absolute (horizontal) values. * @param layoutDirection The layout direction. * @return gravity converted to absolute (horizontal) values. */ public static int getAbsoluteGravity(int gravity, int layoutDirection) { int result = gravity; // If layout is script specific and gravity is horizontal relative (START or END) if ((result & RELATIVE_LAYOUT_DIRECTION) > 0) { if ((result & Gravity.START) == Gravity.START) { // Remove the START bit result &= ~START; if (layoutDirection == View.LAYOUT_DIRECTION_RTL) { // Set the RIGHT bit result |= RIGHT; } else { // Set the LEFT bit result |= LEFT; } } else if ((result & Gravity.END) == Gravity.END) { // Remove the END bit result &= ~END; if (layoutDirection == View.LAYOUT_DIRECTION_RTL) { // Set the LEFT bit result |= LEFT; } else { // Set the RIGHT bit result |= RIGHT; } } // Don't need the script specific bit any more, so remove it as we are converting to // absolute values (LEFT or RIGHT) result &= ~RELATIVE_LAYOUT_DIRECTION; } return result; } }