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
4000
.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);
}
}
}

}