core/java/android/text/method/ScrollingMovementMethod.java

/*
 * 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.text.method;

import android.view.MotionEvent;
import android.text.*;
import android.widget.TextView;
import android.view.View;

/**
 * A movement method that interprets movement keys by scrolling the text buffer.
 */
public class ScrollingMovementMethod extends BaseMovementMethod implements MovementMethod {
    private int getTopLine(TextView widget) {
        return widget.getLayout().getLineForVertical(widget.getScrollY());
    }

    private int getBottomLine(TextView widget) {
        return widget.getLayout().getLineForVertical(widget.getScrollY() + getInnerHeight(widget));
    }

    private int getInnerWidth(TextView widget) {
        return widget.getWidth() - widget.getTotalPaddingLeft() - widget.getTotalPaddingRight();
    }

    private int getInnerHeight(TextView widget) {
        return widget.getHeight() - widget.getTotalPaddingTop() - widget.getTotalPaddingBottom();
    }

    private int getCharacterWidth(TextView widget) {
        return (int) Math.ceil(widget.getPaint().getFontSpacing());
    }

    private int getScrollBoundsLeft(TextView widget) {
        final Layout layout = widget.getLayout();
        final int topLine = getTopLine(widget);
        final int bottomLine = getBottomLine(widget);
        if (topLine > bottomLine) {
            return 0;
        }
        int left = Integer.MAX_VALUE;
        for (int line = topLine; line <= bottomLine; line++) {
            final int lineLeft = (int) Math.floor(layout.getLineLeft(line));
            if (lineLeft < left) {
                left = lineLeft;
            }
        }
        return left;
    }

    private int getScrollBoundsRight(TextView widget) {
        final Layout layout = widget.getLayout();
        final int topLine = getTopLine(widget);
        final int bottomLine = getBottomLine(widget);
        if (topLine > bottomLine) {
            return 0;
        }
        int right = Integer.MIN_VALUE;
        for (int line = topLine; line <= bottomLine; line++) {
            final int lineRight = (int) Math.ceil(layout.getLineRight(line));
            if (lineRight > right) {
                right = lineRight;
            }
        }
        return right;
    }

    @Override
    protected boolean left(TextView widget, Spannable buffer) {
        final int minScrollX = getScrollBoundsLeft(widget);
        int scrollX = widget.getScrollX();
        if (scrollX > minScrollX) {
            scrollX = Math.max(scrollX - getCharacterWidth(widget), minScrollX);
            widget.scrollTo(scrollX, widget.getScrollY());
            return true;
        }
        return false;
    }

    @Override
    protected boolean right(TextView widget, Spannable buffer) {
        final int maxScrollX = getScrollBoundsRight(widget) - getInnerWidth(widget);
        int scrollX = widget.getScrollX();
        if (scrollX < maxScrollX) {
            scrollX = Math.min(scrollX + getCharacterWidth(widget), maxScrollX);
            widget.scrollTo(scrollX, widget.getScrollY());
            return true;
        }
        return false;
    }

    @Override
    protected boolean up(TextView widget, Spannable buffer) {
        final Layout layout = widget.getLayout();
        final int top = widget.getScrollY();
        int topLine = layout.getLineForVertical(top);
        if (layout.getLineTop(topLine) == top) {
            // If the top line is partially visible, bring it all the way
            // into view; otherwise, bring the previous line into view.
            topLine -= 1;
        }
        if (topLine >= 0) {
            Touch.scrollTo(widget, layout, widget.getScrollX(), layout.getLineTop(topLine));
            return true;
        }
        return false;
    }

    @Override
    protected boolean down(TextView widget, Spannable buffer) {
        final Layout layout = widget.getLayout();
        final int innerHeight = getInnerHeight(widget);
        final int bottom = widget.getScrollY() + innerHeight;
        int bottomLine = layout.getLineForVertical(bottom);
        if (layout.getLineTop(bottomLine + 1) < bottom + 1) {
            // Less than a pixel of this line is out of view,
            // so we must have tried to make it entirely in view
            // and now want the next line to be in view instead.
            bottomLine += 1;
        }
        if (bottomLine <= layout.getLineCount() - 1) {
            Touch.scrollTo(widget, layout, widget.getScrollX(),
                    layout.getLineTop(bottomLine + 1) - innerHeight);
            return true;
        }
        return false;
    }

    @Override
    protected boolean pageUp(TextView widget, Spannable buffer) {
        final Layout layout = widget.getLayout();
        final int top = widget.getScrollY() - getInnerHeight(widget);
        int topLine = layout.getLineForVertical(top);
        if (topLine >= 0) {
            Touch.scrollTo(widget, layout, widget.getScrollX(), layout.getLineTop(topLine));
            return true;
        }
        return false;
    }

    @Override
    protected boolean pageDown(TextView widget, Spannable buffer) {
        final Layout layout = widget.getLayout();
        final int innerHeight = getInnerHeight(widget);
        final int bottom = widget.getScrollY() + innerHeight + innerHeight;
        int bottomLine = layout.getLineForVertical(bottom);
        if (bottomLine <= layout.getLineCount() - 1) {
            Touch.scrollTo(widget, layout, widget.getScrollX(),
                    layout.getLineTop(bottomLine + 1) - innerHeight);
            return true;
        }
        return false;
    }

    @Override
    protected boolean top(TextView widget, Spannable buffer) {
        final Layout layout = widget.getLayout();
        if (getTopLine(widget) >= 0) {
            Touch.scrollTo(widget, layout, widget.getScrollX(), layout.getLineTop(0));
            return true;
        }
        return false;
    }

    @Override
    protected boolean bottom(TextView widget, Spannable buffer) {
        final Layout layout = widget.getLayout();
        final int lineCount = layout.getLineCount();
        if (getBottomLine(widget) <= lineCount - 1) {
            Touch.scrollTo(widget, layout, widget.getScrollX(),
                    layout.getLineTop(lineCount) - getInnerHeight(widget));
            return true;
        }
        return false;
    }

    @Override
    protected boolean lineStart(TextView widget, Spannable buffer) {
        final int minScrollX = getScrollBoundsLeft(widget);
        int scrollX = widget.getScrollX();
        if (scrollX > minScrollX) {
            widget.scrollTo(minScrollX, widget.getScrollY());
            return true;
        }
        return false;
    }

    @Override
    protected boolean lineEnd(TextView widget, Spannable buffer) {
        final int maxScrollX = getScrollBoundsRight(widget) - getInnerWidth(widget);
        int scrollX = widget.getScrollX();
        if (scrollX < maxScrollX) {
            widget.scrollTo(maxScrollX, widget.getScrollY());
            return true;
        }
        return false;
    }

    @Override
    protected boolean home(TextView widget, Spannable buffer) {
        return top(widget, buffer);
    }

    @Override
    protected boolean end(TextView widget, Spannable buffer) {
        return bottom(widget, buffer);
    }

    @Override
    public boolean onTouchEvent(TextView widget, Spannable buffer, MotionEvent event) {
        return Touch.onTouchEvent(widget, buffer, event);
    }

    @Override
    public void onTakeFocus(TextView widget, Spannable text, int dir) {
        Layout layout = widget.getLayout();

        if (layout != null && (dir & View.FOCUS_FORWARD) != 0) {
            widget.scrollTo(widget.getScrollX(),
                            layout.getLineTop(0));
        }
        if (layout != null && (dir & View.FOCUS_BACKWARD) != 0) {
            int padding = widget.getTotalPaddingTop() +
                          widget.getTotalPaddingBottom();
            int line = layout.getLineCount() - 1;

            widget.scrollTo(widget.getScrollX(),
                            layout.getLineTop(line+1) -
                            (widget.getHeight() - padding));
        }
    }

    public static MovementMethod getInstance() {
        if (sInstance == null)
            sInstance = new ScrollingMovementMethod();

        return sInstance;
    }

    private static ScrollingMovementMethod sInstance;
}