ItemDecoration固定头部(分组+分割线)

参考资料：https://www.jianshu.com/p/b46a4ff7c10a

先来张最终效果图

具体说明代码注释有了，这里就不说了。

1. public class BudgetContrastDataStickHeaderDecoration extends RecyclerView.ItemDecoration {
2. private Context context;
3. private Drawable drawable;
4. private StickHeaderCallBack callBack;
5. private Paint paint;
6. private TextPaint textPaint;
7. private TextPaint.FontMetrics fontMetrics;
8.  
9. public BudgetContrastDataStickHeaderDecoration(Context context, StickHeaderCallBack callBack) {
10. this.context = context;
11. this.callBack = callBack;
12. // 用於獲取分割線高度
13. int[] ATTRS = new int[]{android.R.attr.listDivider};
14. TypedArray typedArray = this.context.obtainStyledAttributes(ATTRS);
15. drawable = typedArray.getDrawable(0);
16. typedArray.recycle();
17. // 分組欄背景顏色
18. paint = new Paint();
19. paint.setColor(this.context.getResources().getColor(R.color.stick_header));
20. // 分組文字
21. textPaint = new TextPaint();
22. // 粗體
23. textPaint.setTypeface(Typeface.DEFAULT_BOLD);
24. // 抗鋸齒
25. textPaint.setAntiAlias(true);
26. // 字體大小
27. textPaint.setTextSize(40);
28. // 字體顏色
29. textPaint.setColor(Color.BLACK);
30. // 用於計算字體基準
31. fontMetrics = new Paint.FontMetrics();
32. textPaint.getFontMetrics(fontMetrics);
33. // 左對齊
34. textPaint.setTextAlign(Paint.Align.LEFT);
35. }
36.  
37. @Override
38. public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
39. super.onDraw(c, parent, state);
40. c.save();
41. int left;
42. int right;
43. // 從DividerItemDecoration源碼抄來,大概為根據Padding切割畫布
44. if (parent.getClipToPadding()) {
45. left = parent.getPaddingLeft();
46. right = parent.getWidth() - parent.getPaddingRight();
47. c.clipRect(left, parent.getPaddingTop(), right,
48. parent.getHeight() - parent.getPaddingBottom());
49. } else {
50. left = 0;
51. right = parent.getWidth();
52. }
53.  
54. int childCount = parent.getChildCount();
55. Rect mBounds = new Rect();
56. for (int i = 0; i < childCount; i++) {
57. View child = parent.getChildAt(i);
58. //獲取itemView的範圍，這個範圍包含margin和offset，它們被保存在mBounds中
59. parent.getDecoratedBoundsWithMargins(child, mBounds);
60. int bottom = mBounds.bottom + Math.round(child.getTranslationY());
61. int top = bottom - drawable.getIntrinsicHeight();
62. drawable.setBounds(left, top, right, bottom);
63. drawable.draw(c);
64. }
65. c.restore();
66. }
67.  
68. @Override
69. public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
70. super.onDrawOver(c, parent, state);
71. c.save();
72. float left;
73. float right;
74. // 從DividerItemDecoration源碼抄來,大概為根據Padding切割畫布
75. if (parent.getClipToPadding()) {
76. left = parent.getPaddingLeft();
77. right = parent.getWidth() - parent.getPaddingRight();
78. c.clipRect(left, parent.getPaddingTop(), right,
79. parent.getHeight() - parent.getPaddingBottom());
80. } else {
81. left = 0;
82. right = parent.getWidth();
83. }
84. // left、right、top、bottom實現Padding 3 的效果
85. left += context.getResources().getDimensionPixelSize(R.dimen.stick_header_padding);
86. right -= context.getResources().getDimensionPixelSize(R.dimen.stick_header_padding);
87. int childCount = parent.getChildCount();
88. for (int i = 0; i < childCount; i++) {
89. View child = parent.getChildAt(i);
90. int position = parent.getChildAdapterPosition(child);
91. String deptName = this.callBack.getDeptName(parent.getAdapter(), position);
92. if (deptName != null && deptName.length() > 0) {
93. /*
94. * 1.position=0 列表的第一個項目始終顯示固定頭部
95. * 2.分組中的第一個項目顯示固定頭部
96. * 3.不是分組中的第一個，且頂部座標已是0或者負數，表示分組中的第一個已經滾動到不可見區域，但分組中其他項目仍然顯示在屏幕上
97. * child.getBottom()+drawable.getIntrinsicHeight()>=0 底部+分隔線>=0 表示該項目還在屏幕中，繼續顯示固定表頭
98. */
99. if (position == 0 || isFirstInGroup(parent.getAdapter(), position) || (!isFirstInGroup(parent.getAdapter(), position) && position > 0 && child.getTop() <= 0 && child.getBottom() + drawable.getIntrinsicHeight() >= 0)) {
100. // 分組欄位是VIEW的頂部座標
101. float bottom = Math.max(child.getTop(), this.context.getResources().getDimensionPixelSize(R.dimen.stick_header_height));
102. float top = bottom - this.context.getResources().getDimensionPixelSize(R.dimen.stick_header_height);
103. // 判斷下一個項目是否當前項目的分組內
104. if (position + 1 < parent.getAdapter().getItemCount() && !this.callBack.getDeptName(parent.getAdapter(), position + 1).equals(deptName)) {
105. float temp = child.getBottom() + drawable.getIntrinsicHeight() - bottom;
106. // 如果不是,判斷當前項目的底部+分割線是否小於固定頭部的底部座標
107. if (temp < 0) {
108. // 相當於移動固定頭部
109. top+=temp;
110. bottom+=temp;
111. }
112. }
113. top += context.getResources().getDimensionPixelSize(R.dimen.stick_header_padding);
114. bottom -= context.getResources().getDimensionPixelSize(R.dimen.stick_header_padding);
115. // 畫圓角方塊,rx:橢圓的短半徑,ry:橢圓的長半徑
116. c.drawRoundRect(left, top, right, bottom, 50, 80, this.paint);
117. float baseline = top + (bottom - top - fontMetrics.bottom + fontMetrics.top) / 2 - fontMetrics.top;
118. // left + 30 字體偏移,隨個人喜歡
119. c.drawText(deptName, left + 30, baseline, textPaint);
120. }
121. }
122. }
123. c.restore();
124. }
125.  
126. @Override
127. public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
128. super.getItemOffsets(outRect, view, parent, state);
129. int stickHeaderHeight = 0;
130. int position = parent.getChildAdapterPosition(view);
131. String deptName = this.callBack.getDeptName(parent.getAdapter(), position);
132. if (deptName != null && deptName.length() > 0) {
133. if (position == 0 || isFirstInGroup(parent.getAdapter(), position)) {
134. stickHeaderHeight = this.context.getResources().getDimensionPixelSize(R.dimen.stick_header_height);
135. }
136. }
137. if (drawable == null) {
138. outRect.set(0, stickHeaderHeight, 0, 0);
139. return;
140. }
141. outRect.set(0, stickHeaderHeight, 0, drawable.getIntrinsicHeight());
142. }
143.  
144. /**
145. * 是否分組中的第一個
146. *
147. * @param adapter RecyclerView適配器
148. * @param position 項目序號
149. * @return true or false
150. */
151. private boolean isFirstInGroup(RecyclerView.Adapter adapter, int position) {
152. if (position == 0) {
153. return true;
154. } else {
155. String previousDeptName = this.callBack.getDeptName(adapter, position - 1);
156. String deptName = this.callBack.getDeptName(adapter, position);
157. return !deptName.equals(previousDeptName);
158. }
159. }
160.  
161. public interface StickHeaderCallBack {
162. String getDeptName(RecyclerView.Adapter adapter, int position);
163. }
164. }

 

实现的接口StickHeaderCallBack就是return一个字符串。

1. @Override
2. public String getDeptName(RecyclerView.Adapter adapter, int position) {
3. if (adapter instanceof BudgetAdapter) {
4. BudgetAdapter budgetAdapter = (BudgetAdapter) adapter;
5. return budgetAdapter.budgetItemDataList.get(position).getDept_name();
6. } else {
7. return "";
8. }
9. }

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