每秒设置textview的文本时，防止除textview之外的其他视图更新/重绘

Question

我有一个稍微复杂的布局，包含几个自定义视图，每个视图计算它们需要多少空间等等。在这个布局的顶部，我有一个 TextView，它应该从 02:04:20 (hh:mm:ss) 开始倒计时，并每秒更新一次。

我的问题不是更新文本，问题是当我更新文本时，布局中的所有视图都会重新绘制。此外，我在此布局中使用画廊，因此在与画廊交互时当文本更新时，图库会立即切换到您选择的位置（即使您正在切换到图库中的新项目）。

那么..如何更新textview而不使其他视图重新绘制？

Answer 1

如果视图的宽度是固定的并且视图的高度不会改变，那么 TextView 不会使 setText() 上的整个布局无效。将布局参数 android:layout_width 从 "wrap_content" 更改为固定宽度，例如 "fill_parent" 或 "100sp"。

来源：

/**
 * Check whether entirely new text requires a new view layout
 * or merely a new text layout.
 */

private void checkForRelayout() {
    // If we have a fixed width, we can just swap in a new text layout
    // if the text height stays the same or if the view height is fixed.

    if ((mLayoutParams.width != LayoutParams.WRAP_CONTENT ||
            (mMaxWidthMode == mMinWidthMode && mMaxWidth == mMinWidth)) &&
            (mHint == null || mHintLayout != null) &&
            (mRight - mLeft - getCompoundPaddingLeft() - getCompoundPaddingRight() > 0)) {
        // Static width, so try making a new text layout.

        int oldht = mLayout.getHeight();
        int want = mLayout.getWidth();
        int hintWant = mHintLayout == null ? 0 : mHintLayout.getWidth();

        /*
         * No need to bring the text into view, since the size is not
         * changing (unless we do the requestLayout(), in which case it
         * will happen at measure).
         */
        makeNewLayout(want, hintWant, UNKNOWN_BORING, UNKNOWN_BORING,
                      mRight - mLeft - getCompoundPaddingLeft() - getCompoundPaddingRight(),
                      false);

        if (mEllipsize != TextUtils.TruncateAt.MARQUEE) {
            // In a fixed-height view, so use our new text layout.
            if (mLayoutParams.height != LayoutParams.WRAP_CONTENT &&
                mLayoutParams.height != LayoutParams.MATCH_PARENT) {
                invalidate();
                return;
            }

            // Dynamic height, but height has stayed the same,
            // so use our new text layout.
            if (mLayout.getHeight() == oldht &&
                (mHintLayout == null || mHintLayout.getHeight() == oldht)) {
                invalidate();
                return;
            }
        }

        // We lose: the height has changed and we have a dynamic height.
        // Request a new view layout using our new text layout.
        requestLayout();
        invalidate();
    } else {
        // Dynamic width, so we have no choice but to request a new
        // view layout with a new text layout.

        nullLayouts();
        requestLayout();
        invalidate();
    }
}