Android(安卓)RecyclerView ItemDecoration timeline（一）

package zhangphil.book;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.Rect;import android.graphics.drawable.ColorDrawable;import android.graphics.drawable.Drawable;import android.os.Bundle;import android.support.annotation.NonNull;import android.support.v4.content.ContextCompat;import android.support.v7.app.AppCompatActivity;import android.support.v7.widget.LinearLayoutManager;import android.support.v7.widget.RecyclerView;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.TextView;public class MainActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        RecyclerView mRecyclerView = findViewById(R.id.recycler_view);        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getApplicationContext());        linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);        mRecyclerView.setLayoutManager(linearLayoutManager);        RecyclerViewAdapter adapter = new RecyclerViewAdapter();        mRecyclerView.setAdapter(adapter);        RVItemDecoration mRVItemDecoration = new RVItemDecoration(getApplicationContext());        mRecyclerView.addItemDecoration(mRVItemDecoration);    }    private class RecyclerViewAdapter extends RecyclerView.Adapter {        @NonNull        @Override        public RecyclerViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {            View view = LayoutInflater.from(getApplicationContext()).inflate(android.R.layout.simple_list_item_1, parent, false);            RecyclerViewHolder holder = new RecyclerViewHolder(view);            return holder;        }        @Override        public void onBindViewHolder(@NonNull RecyclerViewHolder holder, int position) {            holder.text1.setText(position + "");        }        @Override        public int getItemCount() {            return Integer.MAX_VALUE;        }    }    private class RecyclerViewHolder extends RecyclerView.ViewHolder {        public TextView text1;        public RecyclerViewHolder(View itemView) {            super(itemView);            text1 = itemView.findViewById(android.R.id.text1);        }    }    private class RVItemDecoration extends RecyclerView.ItemDecoration {        private Drawable mDrawable;        //轴线距离左侧的距离，单位pix。        private int marginLeft = 20;        //轴线的宽度，单位pix。        private int lineSize = 10;        private Paint mPaint;        public RVItemDecoration(Context context) {            mPaint = new Paint();            mPaint.setAntiAlias(true);            mPaint.setColor(Color.RED);            mDrawable = new ColorDrawable(ContextCompat.getColor(getApplicationContext(), android.R.color.holo_blue_light));        }        @Override        public void onDraw(Canvas canvas, RecyclerView parent, RecyclerView.State state) {            canvas.save();            int childCount = parent.getChildCount();            for (int i = 0; i < childCount; i++) {                View child = parent.getChildAt(i);                //先画线。                mDrawable.setBounds(marginLeft, child.getTop(), marginLeft + lineSize, child.getBottom());                mDrawable.draw(canvas);                //后画覆盖在线上的圆球。                canvas.drawCircle(marginLeft + lineSize / 2, (child.getTop() + child.getBottom()) / 2, (lineSize + marginLeft) / 2, mPaint);            }            canvas.restore();        }        /**         * outRect.set()函数相当于给RecyclerView的每一个item的View四周设置margin值。         * 此处的margin值不同于onDraw里面的margin，onDraw里面给mDrawable设置的margin，仅仅是针对分割条而言。         *         * @param outRect         * @param view         * @param parent         * @param state         */        @Override        public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {            outRect.set((marginLeft + lineSize) * 2, 0, 0, 0);            //测试。给RecyclerView的每一个item设置一个浅灰色背景。            //便于观察绘制结果。            view.setBackgroundColor(Color.LTGRAY);        }    }}
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