android.widget.TextView#scrollTo ( )源码实例Demo

@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));
    }
}
 

/**
 * Performs a scroll left action.
 * Scrolls left by the specified number of characters.
 *
 * @param widget The text view.
 * @param buffer The text buffer.
 * @param amount The number of characters to scroll by.  Must be at least 1.
 * @return True if the event was handled.
 * @hide
 */
protected boolean scrollLeft(TextView widget, Spannable buffer, int amount) {
    final int minScrollX = getScrollBoundsLeft(widget);
    int scrollX = widget.getScrollX();
    if (scrollX > minScrollX) {
        scrollX = Math.max(scrollX - getCharacterWidth(widget) * amount, minScrollX);
        widget.scrollTo(scrollX, widget.getScrollY());
        return true;
    }
    return false;
}
 

/**
 * Performs a scroll right action.
 * Scrolls right by the specified number of characters.
 *
 * @param widget The text view.
 * @param buffer The text buffer.
 * @param amount The number of characters to scroll by.  Must be at least 1.
 * @return True if the event was handled.
 * @hide
 */
protected boolean scrollRight(TextView widget, Spannable buffer, int amount) {
    final int maxScrollX = getScrollBoundsRight(widget) - getInnerWidth(widget);
    int scrollX = widget.getScrollX();
    if (scrollX < maxScrollX) {
        scrollX = Math.min(scrollX + getCharacterWidth(widget) * amount, maxScrollX);
        widget.scrollTo(scrollX, widget.getScrollY());
        return true;
    }
    return false;
}
 

/**
 * Performs a scroll to line start action.
 * Scrolls to the start of the line.
 *
 * @param widget The text view.
 * @param buffer The text buffer.
 * @return True if the event was handled.
 * @hide
 */
protected boolean scrollLineStart(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;
}
 

/**
 * Performs a scroll to line end action.
 * Scrolls to the end of the line.
 *
 * @param widget The text view.
 * @param buffer The text buffer.
 * @return True if the event was handled.
 * @hide
 */
protected boolean scrollLineEnd(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;
}
 

private void addText(TextView textView, String content) {
    textView.append(content);
    textView.append("\n");
    int offset = textView.getLineCount() * textView.getLineHeight();
    if (offset > textView.getHeight()) {
        textView.scrollTo(0, offset - textView.getHeight());
    }
}
 

/**
 * Scrolls the specified widget to the specified coordinates, except
 * constrains the X scrolling position to the horizontal regions of
 * the text that will be visible after scrolling to the specified
 * Y position.
 */
public static void scrollTo(TextView widget, Layout layout, int x, int y) {
    final int horizontalPadding = widget.getTotalPaddingLeft() + widget.getTotalPaddingRight();
    final int availableWidth = widget.getWidth() - horizontalPadding;

    final int top = layout.getLineForVertical(y);
    Alignment a = layout.getParagraphAlignment(top);
    boolean ltr = layout.getParagraphDirection(top) > 0;

    int left, right;
    if (widget.getHorizontallyScrolling()) {
        final int verticalPadding = widget.getTotalPaddingTop() + widget.getTotalPaddingBottom();
        final int bottom = layout.getLineForVertical(y + widget.getHeight() - verticalPadding);

        left = Integer.MAX_VALUE;
        right = 0;

        for (int i = top; i <= bottom; i++) {
            left = (int) Math.min(left, layout.getLineLeft(i));
            right = (int) Math.max(right, layout.getLineRight(i));
        }
    } else {
        left = 0;
        right = availableWidth;
    }

    final int actualWidth = right - left;

    if (actualWidth < availableWidth) {
        if (a == Alignment.ALIGN_CENTER) {
            x = left - ((availableWidth - actualWidth) / 2);
        } else if ((ltr && (a == Alignment.ALIGN_OPPOSITE)) ||
                   (!ltr && (a == Alignment.ALIGN_NORMAL)) ||
                   (a == Alignment.ALIGN_RIGHT)) {
            // align_opposite does NOT mean align_right, we need the paragraph
            // direction to resolve it to left or right
            x = left - (availableWidth - actualWidth);
        } else {
            x = left;
        }
    } else {
        x = Math.min(x, right - availableWidth);
        x = Math.max(x, left);
    }

    widget.scrollTo(x, y);
}