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我們都知道，使用 RecyclerView 時(shí) ，我們不能像 ListView 那樣通過 setDivider() 的方式來設(shè)置分割線，好在 Android 為我們提供了定制性更強(qiáng)的 ItemDecoration 來為 RecyclerView 設(shè)置分割線。

什么是 ItemDecoration ?

顧名思義 ItemDecoration 就是 Item 的裝飾，我們可以在 Item 的上下左右添加自定義的裝飾，比如橫線，圖案。同時(shí)系統(tǒng)已經(jīng)為我們提供了一個(gè) DividerItemDecoration, 如果這個(gè) DividerItemDecoration 不滿足我們的需求，我們就可以通過自定義 ItemDecoration 來實(shí)現(xiàn)了。

下面我們看下系統(tǒng)的 DividerItemDecoration ：

引入 DividerItemDecoration(系統(tǒng)提供)

DividerItemDecoration 的使用非常簡單，只需添加下面代碼即可：

DividerItemDecoration decoration = new DividerItemDecoration(this,DividerItemDecoration.VERTICAL);
recyclerView.addItemDecoration(decoration);

效果：

DividerItemDecoration.png

如果想要修改 DividerItemDecoration 的顏色和高度，可以調(diào)用它的 setDrawable(drawable) 設(shè)置一個(gè) Drawable 對象

// MainActivity.java
DividerItemDecoration decoration = new DividerItemDecoration(this, DividerItemDecoration.VERTICAL);
Drawable dividerDrawable = getResources().getDrawable(R.drawable.drawable_divider);
decoration.setDrawable(dividerDrawable);
recyclerView.addItemDecoration(decoration);

// res/drawable/drawable_divider.xml
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    android:shape="rectangle">
    <!-- 漸變色 -->
    <gradient
        android:angle="135"
        android:centerColor="#4CAF50"
        android:endColor="#2E7D32"
        android:startColor="#81C784"
        android:type="linear" />

    <size android:height="1dp" />
</shape>

效果:

dividerItemDecoration-drawable.png

自定義 ItemDecoration

自定義 ItemDecoration ，主要需要重寫以下三個(gè)方法：

/**
 * 自定義 ItemDecoration
 */
public class LinearItemDecoration extends RecyclerView.ItemDecoration {

    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
    }

    @Override
    public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.onDraw(c, parent, state);
    }

    @Override
    public void onDrawOver(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.onDrawOver(c, parent, state);
    }

1. getItemOffsets()

getItemOffsets() 主要作用是在 item 的四周留下邊距，效果和 margin 類似，item 的四周留下邊距后，我們就可以通過 onDraw() 在這個(gè)邊距上繪制了。

public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state)

(1) 參數(shù) Rect outRect : 表示 item 的上下左右所留下的邊距。其中 outRect 的 left, top,right,bottom 即為 item 四周留下的邊距的距離，默認(rèn)都為 0 ；示意圖如下：

(2) 參數(shù) View view : 指當(dāng)前 item 的 View 對象；

(3) 參數(shù) RecyclerView parent : 指 RecyclerView 本身；

(4) RecyclerView.State state : 指 RecyclerView 當(dāng)前的狀態(tài)；

1.1 getItemOffsets() 應(yīng)用例子：

既然 getItemOffsets(Rect outRect) 方法可以設(shè)置 item 四周的邊距大小，那就可以設(shè)置 recyclerview 背景色和 item 四周的邊距，使得 item 四周的邊距透出 recyclerview 背景色來達(dá)到分割線的目的。

當(dāng)然 item 的背景色需要和 recyclerview 的背景色不一致才有效果；

首先將 recyclerview 的背景色設(shè)置為 colorAccent 紅色, 將 item 的背景色設(shè)置為白色：

<!--- activity_main.xml -----> 
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_recycler"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/colorAccent" />

</android.support.constraint.ConstraintLayout>

<!--- item_recycler.xml -----> 
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:background="#fff"
    android:gravity="center_vertical"
    android:orientation="vertical">

    <TextView
        android:id="@+id/tv_title"
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:gravity="center_vertical" />

</LinearLayout>

然后繼承 ItemDecoration 類，重寫 getOffsets() 方法，將 outRect 的上邊距 top 設(shè)置為 10px;

/**
 * 自定義 ItemDecoration
 */
public class LinearItemDecoration extends RecyclerView.ItemDecoration {

    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        outRect.top = 10;   // 10px
    }
}

最后將這個(gè) LinearItemDecoration 添加到 RecyclerView 中：

LinearItemDecoration decoration = new LinearItemDecoration();
recyclerView.addItemDecoration(decoration);

效果如下(下方的紅色是因?yàn)镽ecyclerView 高度為 match_parent ,但 item 數(shù)據(jù)只有 5 條)：

linearItemDecoration.png

從效果圖可以看出：每一個(gè) item 的頂部都有一個(gè)紅色的背景線，包括第一個(gè) item 頂部也有(怎么解決呢？見 2.1 節(jié)詳解)，

同理，我們可以設(shè)置為底部 10px,左側(cè) 20px ,右側(cè) 40px；

public class LinearItemDecoration extends RecyclerView.ItemDecoration {

    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        outRect.bottom = 10;
        outRect.left = 20;
        outRect.right = 40;
    }
}

效果：

linearItemDecoration-bottom-left-right.png

可以看到：每個(gè) item 的左測，底部，右側(cè)都有了間距，露出了 RecyclerView 的背景色了。

2. onDraw()

@Override
public void onDraw(@NonNull Canvas canvas, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
   super.onDraw(canvas, parent, state);
}

onDraw() 函數(shù)中的 parent , state 參數(shù)和 getItemOffsets() 方法中的參數(shù)含義是一樣的，canvas 參數(shù)是 getItemOffsets() 函數(shù)所留下的左右上下的空白區(qū)域?qū)?yīng)的 Canvas 畫布對象。我們可以在這個(gè)區(qū)域中利用 Paint 畫筆繪制任何圖形。

比如在 item 左側(cè)繪制一個(gè) 空心圓。

/**
 * 自定義 ItemDecoration
 */
public class LinearItemDecoration extends RecyclerView.ItemDecoration {

    private static final String TAG = "LinearItemDecoration";
    private Paint paint;

    public LinearItemDecoration() {
        paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(Color.BLUE);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(5);
    }

    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        Log.e(TAG, "getItemOffsets: " );
        outRect.bottom = 10;
        outRect.left = 100;
        outRect.right = 40;
    }

    @Override
    public void onDraw(@NonNull Canvas canvas, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.onDraw(canvas, parent, state);
        Log.e(TAG, "onDraw: ");
        for (int i = 0; i < parent.getChildCount(); i++) {
            View childView = parent.getChildAt(i);
            canvas.drawCircle(50, childView.getTop() + childView.getHeight() / 2, 20, paint);
        }

    }
}

效果：

onDraw-circle.png

我們在 getItemOffsets() 和 onDraw() 方法中都添加了日志，日志打印如下：

log.png

從日志中可以看出： getItemOffsets() 方法執(zhí)行了 5 遍，和數(shù)據(jù)源個(gè)數(shù)是一樣的，但 onDraw() 方法只執(zhí)行了一遍，由此我們知道， getItemOffsets() 是針對每個(gè) item 都會執(zhí)行一次，也就是說每個(gè) item 的 outRect 可以設(shè)置為不同值，但是 onDraw(),onDrawOver() 是針對 ItemDecoration 的，不是針對 item 的，只執(zhí)行一次。所以我們在 onDraw() ,onDrawOver() 中繪制的時(shí)候，需要遍歷每個(gè) item 進(jìn)行繪制。

優(yōu)雅獲取 outRect 中的值

在上面例子中，我們在 onDraw 中獲取 outRect 中的值都是寫成計(jì)算好的固定值，顯然這種硬編碼的方式不利于擴(kuò)展，其實(shí)，我們可以通過 LayoutManager 來獲取 getItemOffsets() 中設(shè)置的 outRect 的值。

@Override
public void onDraw(@NonNull Canvas canvas, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
    super.onDraw(canvas, parent, state);
    Log.e(TAG, "onDraw: ");
    RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
    for (int i = 0; i < parent.getChildCount(); i++) {
        View childView = parent.getChildAt(i);
         int leftDecorationWidth = layoutManager.getLeftDecorationWidth(childView);
         int topDecorationHeight = layoutManager.getTopDecorationHeight(childView);
         int rightDecorationWidth = layoutManager.getRightDecorationWidth(childView);
         int bottomDecorationHeight = layoutManager.getBottomDecorationHeight(childView);
    }
}

上面硬編碼可以改成：

@Override
public void onDraw(@NonNull Canvas canvas, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
    super.onDraw(canvas, parent, state);
    Log.e(TAG, "onDraw: ");
    RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
    for (int i = 0; i < parent.getChildCount(); i++) {
        View childView = parent.getChildAt(i);
        int leftDecorationWidth = layoutManager.getLeftDecorationWidth(childView);
        int left = leftDecorationWidth / 2;
        canvas.drawCircle(left, childView.getTop() + childView.getHeight() / 2, 20, paint);
    }
}

2.1 擴(kuò)展1 -- 減少背景設(shè)置，避免過度繪制

為了減少過度繪制，我們將 activity_main 中 RecyclerView , item_recycler 中的背景全部去掉，不設(shè)置任何背景，然后在 LinearItemDecoration 中進(jìn)行純繪制分割線，代碼如下：

public class LinearItemDecoration extends RecyclerView.ItemDecoration {

    private static final String TAG = "LinearItemDecoration";
    private Paint paint;
    private Paint dividerPaint;

    public LinearItemDecoration() {
        paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(Color.BLUE);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(5);

        dividerPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        dividerPaint.setColor(Color.parseColor("#e6e6e6"));
        dividerPaint.setStyle(Paint.Style.FILL);
    }

    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        Log.e("ItemOffsets", "getItemOffsets: ");
        outRect.bottom = 5;
        outRect.left = 100;
    }

    @Override
    public void onDraw(@NonNull Canvas canvas, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.onDraw(canvas, parent, state);
        Log.e(TAG, "onDraw: ");
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        for (int i = 0; i < parent.getChildCount(); i++) {
            View childView = parent.getChildAt(i);
            int leftDecorationWidth = layoutManager.getLeftDecorationWidth(childView);
            int topDecorationHeight = layoutManager.getTopDecorationHeight(childView);
            int rightDecorationWidth = layoutManager.getRightDecorationWidth(childView);
            int bottomDecorationHeight = layoutManager.getBottomDecorationHeight(childView);
            int left = leftDecorationWidth / 2;
            canvas.drawCircle(left, childView.getTop() + childView.getHeight() / 2, 20, paint);
            // getItemOffsets()中的設(shè)置的是 bottom = 5px;所以在 drawRect 時(shí)，top 為 childView.getBottom,bottom為top+bottomDecorationHeight
            canvas.drawRect(new Rect(
                    leftDecorationWidth,
                    childView.getBottom(),
                    childView.getWidth() + leftDecorationWidth,
                    childView.getBottom() + bottomDecorationHeight
            ), dividerPaint);
        }
    }

    @Override
    public void onDrawOver(@NonNull Canvas canvas, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.onDrawOver(canvas, parent, state);
    }
}

效果：

divider-draw.png

注意： 上面 getItemOffsets() 中設(shè)置的是 bottom = 5px; 所以在 onDraw() 方法的 drawRect 時(shí)，top值為 childView.getBottom, bottom值為 top+bottomDecorationHeight。

divider-top-bottom.png

同理：getItemOffsets() 中設(shè)置是 top = 5px，那么在 onDraw() 方法 drawRect 時(shí)，bottom 值為 childView.getTop() , top 值為 bottom - topDecorationHeight

2.2 擴(kuò)展2 -- 實(shí)現(xiàn)豎直進(jìn)度分割線

在 getItemOffsets() 方法中左側(cè)留下空白區(qū)域，然后在 onDraw() 方法中繪制圓和豎線。代碼如下：

<!--- item_recycler.xml ---->
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@android:color/white"
    android:gravity="center_vertical"
    android:orientation="vertical"
    android:padding="10dp">

    <TextView
        android:id="@+id/tv_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textColor="#332"
        android:textSize="16sp"
        tools:text="我是 title" />

    <TextView
        android:id="@+id/tv_time"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dp"
        android:gravity="center_vertical"
        android:textColor="#666"
        android:textSize="14sp"
        tools:text="woshi" />

</LinearLayout>

<!--- activity_main.xml --->
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_recycler"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#dfdfdf" />

</android.support.constraint.ConstraintLayout>

// ProgressItemDecoration.java
public class ProgressItemDecoration extends RecyclerView.ItemDecoration {

    private Context context;
    private Paint circlePaint;
    private Paint linePaint;
    private int radius;
    private int curPosition = 0;   // 當(dāng)前進(jìn)行中的位置

    public ProgressItemDecoration(Context context) {
        this.context = context;
        circlePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        circlePaint.setColor(context.getResources().getColor(R.color.colorPrimary));
        circlePaint.setStyle(Paint.Style.FILL);
        radius = dp2Px(8);
        circlePaint.setStrokeWidth(dp2Px(2));


        linePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        linePaint.setColor(context.getResources().getColor(R.color.colorPrimary));
        linePaint.setStrokeWidth(dp2Px(2));
    }

    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        outRect.top = dp2Px(20);
        outRect.left = dp2Px(50);
        outRect.right = dp2Px(20);

    }

    @Override
    public void onDraw(@NonNull Canvas canvas, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.onDraw(canvas, parent, state);
        int childCount = parent.getChildCount();
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        for (int i = 0; i < childCount; i++) {
            View childView = parent.getChildAt(i);
            int leftDecorationWidth = layoutManager.getLeftDecorationWidth(childView);
            int topDecorationHeight = layoutManager.getTopDecorationHeight(childView);
            // 獲取當(dāng)前 item 是 recyclerview 的第幾個(gè) childview
            int childLayoutPosition = parent.getChildLayoutPosition(childView);
            float startX = leftDecorationWidth / 2;
            float stopX = startX;
            // 圓頂部部分豎線，起點(diǎn) Y
            float topStartY = childView.getTop() - topDecorationHeight;
            // 圓頂部部分豎線，終點(diǎn) Y
            float topStopY = childView.getTop() + childView.getHeight() / 2 - radius;

            // 圓底部部分豎線，起點(diǎn) Y
            float bottomStartY = childView.getTop() + childView.getHeight() / 2 + radius;
            // 圓底部部分豎線，終點(diǎn) Y
            float bottomStopY = childView.getBottom();

            // 位置超過 curPosition 時(shí)，豎線顏色設(shè)置為淺色
            if (childLayoutPosition > curPosition) {
                linePaint.setColor(context.getResources().getColor(R.color.colorPrimaryTint));
                circlePaint.setColor(context.getResources().getColor(R.color.colorPrimaryTint));
                circlePaint.setStyle(Paint.Style.STROKE);
            } else {
                linePaint.setColor(context.getResources().getColor(R.color.colorPrimary));
                circlePaint.setColor(context.getResources().getColor(R.color.colorPrimary));
                circlePaint.setStyle(Paint.Style.FILL);
            }

            // 繪制圓
            if (childLayoutPosition == curPosition) {
                circlePaint.setStyle(Paint.Style.STROKE);
                canvas.drawCircle(leftDecorationWidth / 2, childView.getTop() + childView.getHeight() / 2, dp2Px(2), circlePaint);
            }
            canvas.drawCircle(leftDecorationWidth / 2, childView.getTop() + childView.getHeight() / 2, radius, circlePaint);

            // 繪制豎線 , 第 0 位置上只需繪制 下半部分
            if (childLayoutPosition == 0) {
                // 當(dāng)前 item position = curPosition 時(shí)，繪制下半部分豎線時(shí)，顏色設(shè)置為淺色
                if (childLayoutPosition == curPosition) {
                    linePaint.setColor(context.getResources().getColor(R.color.colorPrimaryTint));
                }
                canvas.drawLine(startX, bottomStartY, startX, bottomStopY, linePaint);
                // 最后位置上，只需繪制上半部分
            } else if (childLayoutPosition == parent.getAdapter().getItemCount() - 1) {
                canvas.drawLine(startX, topStartY, startX, topStopY, linePaint);
            } else {
                // 都要繪制
                canvas.drawLine(startX, topStartY, startX, topStopY, linePaint);
                // 當(dāng)前 item position = curPosition 時(shí)，繪制下半部分豎線時(shí)，顏色設(shè)置為淺色
                if (childLayoutPosition == curPosition) {
                    linePaint.setColor(context.getResources().getColor(R.color.colorPrimaryTint));
                }
                canvas.drawLine(startX, bottomStartY, startX, bottomStopY, linePaint);
            }
        }

    }

    /**
     * 設(shè)置進(jìn)行中的位置
     *
     * @param recyclerView
     * @param position
     */
    public void setDoingPosition(RecyclerView recyclerView, int position) {
        if (recyclerView == null) {
            throw new IllegalArgumentException("RecyclerView can't be null");
        }
        if (recyclerView.getAdapter() == null) {
            throw new IllegalArgumentException("RecyclerView Adapter can't be null");
        }
        if (position < 0) {
            throw new IllegalArgumentException("position can't be less than 0");
        }
        recyclerView.getLayoutManager().getItemCount();
        if (position > recyclerView.getAdapter().getItemCount() - 1) {
            throw new IllegalArgumentException("position can't be greater than item count");
        }
        this.curPosition = position;
    }

    private int dp2Px(int value) {
        return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, value, context.getResources().getDisplayMetrics());
    }
}

// MainActivity.java
public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        RecyclerView recyclerView = findViewById(R.id.rv_recycler);
        recyclerView.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));
        List<String> list = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            String data = "test data  - " + i;
            if (i % 2 == 0) {
                data = data + "\n" + "這是測試數(shù)據(jù) " + i;
            }
            list.add(data);
        }
        BaseRecyclerAdapter adapter = new BaseRecyclerAdapter<String>(list, R.layout.item_recycler) {

            @Override
            protected void bind(BaseRecyclerAdapter<String> adapter, BaseViewHolder holder, String data, int position) {
                holder.setText(R.id.tv_title, data);
                holder.setText(R.id.tv_time, new Date().toString());
            }
        };
        recyclerView.setAdapter(adapter);
        ProgressItemDecoration decoration = new ProgressItemDecoration(this);
        decoration.setDoingPosition(recyclerView, 0);
        recyclerView.addItemDecoration(decoration);
    }
}

效果：

vertical-progress.gif

3. onDrawOver()

當(dāng)我們將上面例子中繪制左側(cè)的空心圓的位置改為：圓心 x 坐標(biāo)為 leftDecorationWidth，同時(shí)將 item 背景色設(shè)置為白色：

 @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        Log.e("ItemOffsets", "getItemOffsets: ");
        outRect.bottom = 5;
        outRect.left = 100;
    }

    @Override
    public void onDraw(@NonNull Canvas canvas, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.onDraw(canvas, parent, state);
        Log.e(TAG, "onDraw: ");
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        for (int i = 0; i < parent.getChildCount(); i++) {
            View childView = parent.getChildAt(i);
            int leftDecorationWidth = layoutManager.getLeftDecorationWidth(childView);
            int bottomDecorationHeight = layoutManager.getBottomDecorationHeight(childView);
            int left = leftDecorationWidth / 2;
//            canvas.drawCircle(left, childView.getTop() + childView.getHeight() / 2, 20, paint);
            canvas.drawCircle(leftDecorationWidth, childView.getTop() + childView.getHeight() / 2, 20, paint);
            // getItemOffsets()中的設(shè)置的是 bottom = 5px;所以在 drawRect 時(shí)，top 為 childView.getBottom,bottom為top+bottomDecorationHeight
            canvas.drawRect(new Rect(
                    leftDecorationWidth,
                    childView.getBottom(),
                    childView.getWidth() + leftDecorationWidth,
                    childView.getBottom() + bottomDecorationHeight
            ), dividerPaint);
        }
    }

效果：

draw-leftDecoration-width.png

我們發(fā)現(xiàn)：繪制的空心圓被 item 遮擋了右邊部分，變?yōu)椴豢梢娏?，這是因?yàn)樵谶@個(gè)繪制的流程中，先調(diào)用 ItemDecoration 的 onDraw() 方法，然后再調(diào)用 item 的 onDraw() 方法，最后再調(diào)用 ItemDecoration 的 onDrawOver() 方法。

因此，當(dāng)我們想要在 item 的繪制顯示一些內(nèi)容時(shí)，將繪制的邏輯寫在 onDrawOver() 方法即可。

下面我們實(shí)現(xiàn)在 item 與左側(cè) decoration 交匯處繪制一個(gè) apple icon ,并將 item 中的內(nèi)容文本設(shè)置為居中顯示，代碼如下：

public class LinearItemDecoration extends RecyclerView.ItemDecoration {

    private static final String TAG = "LinearItemDecoration";
    private Paint paint;
    private Paint dividerPaint;
    private Bitmap iconBitmap;

    public LinearItemDecoration(Context context) {
        paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(Color.BLUE);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(5);

        dividerPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        dividerPaint.setColor(Color.parseColor("#e6e6e6"));
        dividerPaint.setStyle(Paint.Style.FILL);

        iconBitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.ios);
    }

    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        Log.e("ItemOffsets", "getItemOffsets: ");
        outRect.bottom = 5;
        outRect.left = 100;
    }

    @Override
    public void onDraw(@NonNull Canvas canvas, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.onDraw(canvas, parent, state);
        Log.e(TAG, "onDraw: ");
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        for (int i = 0; i < parent.getChildCount(); i++) {
            View childView = parent.getChildAt(i);
            int leftDecorationWidth = layoutManager.getLeftDecorationWidth(childView)；
            int bottomDecorationHeight = layoutManager.getBottomDecorationHeight(childView);
            int left = leftDecorationWidth / 2;
//            canvas.drawCircle(left, childView.getTop() + childView.getHeight() / 2, 20, paint);
//            canvas.drawCircle(leftDecorationWidth, childView.getTop() + childView.getHeight() / 2, 20, paint);

            // getItemOffsets()中的設(shè)置的是 bottom = 5px;所以在 drawRect 時(shí)，top 為 childView.getBottom,bottom為top+bottomDecorationHeight
            canvas.drawRect(new Rect(
                    leftDecorationWidth,
                    childView.getBottom(),
                    childView.getWidth() + leftDecorationWidth,
                    childView.getBottom() + bottomDecorationHeight
            ), dividerPaint);
        }
    }

    @Override
    public void onDrawOver(@NonNull Canvas canvas, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.onDrawOver(canvas, parent, state);
        RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        for (int i = 0; i < parent.getChildCount(); i++) {
            View childView = parent.getChildAt(i);
            int leftDecorationWidth = layoutManager.getLeftDecorationWidth(childView);
            canvas.drawBitmap(iconBitmap, leftDecorationWidth - iconBitmap.getWidth() / 2,
                    childView.getTop() + childView.getHeight() / 2 - iconBitmap.getHeight() / 2, paint);
        }
    }
}

效果：

drawover-ios.png

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RecyclerView ItemDecoration 完全解析

RecyclerView ItemDecoration 完全解析

什么是 ItemDecoration ?

引入 DividerItemDecoration(系統(tǒng)提供)

自定義 ItemDecoration

1. getItemOffsets()

1.1 getItemOffsets() 應(yīng)用例子：

2. onDraw()

2.1 擴(kuò)展1 -- 減少背景設(shè)置，避免過度繪制

2.2 擴(kuò)展2 -- 實(shí)現(xiàn)豎直進(jìn)度分割線

3. onDrawOver()

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

色偷偷精品伊人,欧洲久久精品,欧美综合婷婷骚逼,国产AV主播,国产最新探花在线,九色在线视频一区,伊人大交九 欧美,1769亚洲,黄色成人av

RecyclerView ItemDecoration 完全解析

什么是 ItemDecoration ?

引入 DividerItemDecoration(系統(tǒng)提供)

自定義 ItemDecoration

1. getItemOffsets()

1.1 getItemOffsets() 應(yīng)用例子：

2. onDraw()

2.1 擴(kuò)展1 -- 減少背景設(shè)置，避免過度繪制

2.2 擴(kuò)展2 -- 實(shí)現(xiàn)豎直進(jìn)度分割線

3. onDrawOver()

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

色偷偷精品伊人,欧洲久久精品,欧美综合婷婷骚逼,国产AV主播,国产最新探花在线,九色在线视频一区,伊人大交九欧美,1769亚洲,黄色成人av