最近在公司项目里面发现listview里面的textview在调用settext函数的时候非常耗时，当时都有点不敢相信，这是因为如果你把textview设置成wrap_content，则每次调用settext之后会调用到
........40334034 if (mMovement != null) {4035 mMovement.initialize(this, (Spannable) text);40364037 /*4038 * Initializing the movement method will have set the4039 * selection, so reset mSelectionMoved to keep that from4040 * interfering with the normal on-focus selection-setting.4041 */4042 if (mEditor != null) mEditor.mSelectionMoved = false;4043 }4044 }40454046 if (mLayout != null) {
//这个函数非常重要4047 checkForRelayout();4048 }40494050 sendOnTextChanged(text, 0, oldlen, textLength);4051 onTextChanged(text, 0, oldlen, textLength);40524053 notifyViewAccessibilityStateChangedIfNeeded(AccessibilityEvent.CONTENT_CHANGE_TYPE_TEXT);4054
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checkForRelayout函数，这个函数根据文字的多少重新开始布局
6807 private void More ...checkForRelayout() {6808 // If we have a fixed width, we can just swap in a new text layout6809 // if the text height stays the same or if the view height is fixed.68106811 if ((mLayoutParams.width != LayoutParams.WRAP_CONTENT ||6812 (mMaxWidthMode == mMinWidthMode && mMaxWidth == mMinWidth)) &&6813 (mHint == null || mHintLayout != null) &&6814 (mRight - mLeft - getCompoundPaddingLeft() - getCompoundPaddingRight() > 0)) {6815 // Static width, so try making a new text layout.68166817 int oldht = mLayout.getHeight();6818 int want = mLayout.getWidth();6819 int hintWant = mHintLayout == null ? 0 : mHintLayout.getWidth();68206821 /*6822 * No need to bring the text into view, since the size is not6823 * changing (unless we do the requestLayout(), in which case it6824 * will happen at measure).6825 */6826 makeNewLayout(want, hintWant, UNKNOWN_BORING, UNKNOWN_BORING,6827 mRight - mLeft - getCompoundPaddingLeft() - getCompoundPaddingRight(),6828 false);68296830 if (mEllipsize != TextUtils.TruncateAt.MARQUEE) {6831 // In a fixed-height view, so use our new text layout.6832 if (mLayoutParams.height != LayoutParams.WRAP_CONTENT &&6833 mLayoutParams.height != LayoutParams.MATCH_PARENT) {6834 invalidate();6835 return;6836 }68376838 // Dynamic height, but height has stayed the same,6839 // so use our new text layout.6840 if (mLayout.getHeight() == oldht &&6841 (mHintLayout == null || mHintLayout.getHeight() == oldht)) {6842 invalidate();6843 return;6844 }6845 }68466847 // We lose: the height has changed and we have a dynamic height.6848 // Request a new view layout using our new text layout.6849 requestLayout();6850 invalidate();6851 } else {6852 // Dynamic width, so we have no choice but to request a new6853 // view layout with a new text layout.6854 nullLayouts();6855 requestLayout();6856 invalidate();6857 }6858 }
注释已经写的很明白了，所以宽度设定为一个数字或者match_parent能够使得settext所耗时间变短，就是这样。