recyclerview瀑布流_图片二次采样

import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.drawable.BitmapDrawable;import android.os.Build;import android.support.annotation.RequiresApi;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.support.v7.widget.RecyclerView;import android.support.v7.widget.StaggeredGridLayoutManager;import android.util.DisplayMetrics;import android.view.View;import android.view.ViewGroup;import android.widget.LinearLayout;import android.widget.TextView;import java.util.ArrayList;import java.util.List;import java.util.Random;public class MainActivity extends AppCompatActivity {    RecyclerView rv;    List<String> list;    int w_screen;    int h_screen;    int[] array = {R.mipmap.a, R.mipmap.b};    Bitmap[] imgArray = new Bitmap[2];    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        getWindowSize();        rv = (RecyclerView) findViewById(R.id.rv);        getBitmapArray();        initRV();    }    private void getWindowSize() {        DisplayMetrics dm =getResources().getDisplayMetrics();        w_screen = dm.widthPixels;        h_screen = dm.heightPixels;    }    private void getBitmapArray() {        //使用循环遍历目标图片数组 把每一张图片都进行2次采样        for (int i = 0; i < array.length; i++) {            BitmapFactory.Options opt = new BitmapFactory.Options();            //该参数是true 代表是获取图片信息 不真实的解码图片            opt.inJustDecodeBounds = true;            BitmapFactory.decodeResource(getResources(),array[i],opt);            //缩放的比例  要把宽度缩放成屏幕的一般            opt.inSampleSize = opt.outWidth * 2 / w_screen;            opt.inJustDecodeBounds = false;            Bitmap b = BitmapFactory.decodeResource(getResources(), array[i], opt);            imgArray[i] = b;        }    }    private void initRV() {        initData();        StaggeredGridLayoutManager manager = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);        rv.setLayoutManager(manager);        MyRVAdapter adapter = new MyRVAdapter();        rv.setAdapter(adapter);    }    private void initData() {        list = new ArrayList<String>();        for (int i = 0; i < 100; i++) {            list.add("position" + i);        }    }    class MyRVAdapter extends RecyclerView.Adapter<MyRVAdapter.MyViewHolder>{        Random r = new Random();        @Override        public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {            View view = View.inflate(MainActivity.this, R.layout.rv_item, null);            MyViewHolder holder = new MyViewHolder(view);            return holder;        }        @RequiresApi(api = Build.VERSION_CODES.JELLY_BEAN)        @Override        public void onBindViewHolder(MyViewHolder holder, int position) {            holder.tv.setText(list.get(position));            //因为是模拟显示瀑布流 所有使用随机数的形式来模拟            //真正开发时使用的是网络图片  可以直接使用 网络框架例如 ImageLoader 往ImageView上加在图片//            LinearLayout.LayoutParams param = (LinearLayout.LayoutParams) holder.tv.getLayoutParams();//            param.height = r.nextInt(200) + 50;//            holder.tv.setLayoutParams(param);//            holder.tv.setBackgroundResource(array[r.nextInt(2)]);            holder.tv.setBackground(new BitmapDrawable(getResources(),imgArray[r.nextInt(2)]));        }        @Override        public int getItemCount() {            return list == null ? 0 : list.size();        }        public class MyViewHolder extends RecyclerView.ViewHolder{            TextView tv;            public MyViewHolder(View itemView) {                super(itemView);                tv = itemView.findViewById(R.id.tv);            }        }    }}