recyclerview瀑布流_圖片二次採樣

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() {
        //使用循環遍歷目標圖片數組 把每一張圖片都進行2次採樣
        for (int i = 0; i < array.length; i++) {
            BitmapFactory.Options opt = new BitmapFactory.Options();
            //該參數是true 代表是獲取圖片信息 不真實的解碼圖片
            opt.inJustDecodeBounds = true;
            BitmapFactory.decodeResource(getResources(),array[i],opt);
            //縮放的比例  要把寬度縮放成屏幕的一般
            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));

            //因爲是模擬顯示瀑布流 所有使用隨機數的形式來模擬
            //真正開發時使用的是網絡圖片  可以直接使用 網絡框架例如 ImageLoader 往ImageView上加在圖片
//            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);
            }
        }
    }


}