图片二次采样///////////子线程

1.提取的基类

在这里插入代码片package com.example.imager_er;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;

public abstract class BaseActivity extends AppCompatActivity {
    @Override
    protected  void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(getLayoutResId());
        //初始化view
        initView();
        //添加数据
        initData();
    }
    protected abstract int getLayoutResId();
    //初始化view
    protected abstract void initView();
    //添加数据
    protected abstract void initData();
}

2.MainActivity主页面

package com.example.imager_er;

import android.content.Intent;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.net.Uri;
import android.provider.MediaStore;
import android.support.annotation.Nullable;
import android.support.v4.content.CursorLoader;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;

import java.net.URI;

public class MainActivity extends BaseActivity {


    private EditText width;
    private EditText height;
    private Button getImage;
    private Button show;
    private Uri uri;
    private ImageView imageView;
    private String w;
    private String h;

    @Override
    protected int getLayoutResId() {
        return R.layout.activity_main;
    }

    //初始化view
    @Override
    protected void initView() {
        width = findViewById(R.id.width);
        height = findViewById(R.id.height);
        getImage = findViewById(R.id.get_image);
        show = findViewById(R.id.show);
        imageView = findViewById(R.id.image);

    }
    //加载数据
    @Override
    protected void initData() {
        //点击从相册获取图片
        getImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //打开系统相册
                Intent intent = new Intent(Intent.ACTION_PICK);
                //设置类型
                intent.setType("image/*");
                //执行
                startActivityForResult(intent, 100);
            }
        });
        //二次采样
        show.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //获取输入框的值
                w = width.getText().toString();
                h = height.getText().toString();
                if (w.equals("") || h.equals("")) {
                    Toast.makeText(MainActivity.this, "请输入宽，高", Toast.LENGTH_SHORT).show();
                } else {
                    if (uri != null) {
                        String filePath = getUri(uri);
                        NetUtils.getIntance().scaleBitmap(filePath, Integer.parseInt(w),
                                Integer.parseInt(h), new NetUtils.CallBack() {
                                    @Override
                                    public void onSuccess(Bitmap bitmap) {
                                        imageView.setImageBitmap(bitmap);
                                    }
                                }
                        );
                    } else {
                        Toast.makeText(MainActivity.this, "请选择图片", Toast.LENGTH_SHORT).show();
                    }
                }
           }
        });
    }

    //传入图片路径
    private String getUri(Uri contentUri) {
        String[] pr = {MediaStore.Images.Media.DATA};
        CursorLoader loader = new CursorLoader(this, contentUri, pr, null, null, null);
        Cursor cursor = loader.loadInBackground();
        int index = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
        cursor.moveToFirst();
        return cursor.getString(index);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == 100 && resultCode == RESULT_OK) {
            //图片的uri
            uri = data.getData();
            return;
        }
    }
}

3.NetUtils工具类

package com.example.imager_er;

import android.annotation.SuppressLint;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;

public class NetUtils {
    private static NetUtils intance;

    public NetUtils() {
    }

    public static NetUtils getIntance() {
        if(intance == null){
            intance = new NetUtils();
        }
        return intance;
    }
    //图片二次采样
    public Bitmap scaleBitmap(String filePath,int width,int height){
        //第一次直解析bitmap的宽高信息
        BitmapFactory.Options op = new BitmapFactory.Options();
        //指定只解析bitmap的边界信息，不加载bitmap到内存中
        op.inJustDecodeBounds = true;
        BitmapFactory.decodeFile(filePath,op);
        //通过图片的真实宽高信息和需要的宽高产生比例
        op.inSampleSize = Math.max(op.outHeight/height,op.outWidth/width);
        //第二次真正加载图片
        op.inJustDecodeBounds = false;
        Bitmap bitmap = BitmapFactory.decodeFile(filePath,op);
        return bitmap;
    }
    //定义接口
    public interface CallBack{
        void onSuccess(Bitmap bitmap);
    }
    @SuppressLint("StaticFieldLeak")
    public void scaleBitmap(String filePath, final int width, final int height, final CallBack callBack){
        new AsyncTask<String,Void,Bitmap>(){
            @Override
            protected Bitmap doInBackground(String... strings) {
                return scaleBitmap(strings[0],width,height);
            }

            @Override
            protected void onPostExecute(Bitmap bitmap) {
                callBack.onSuccess(bitmap);
            }
        }.execute(filePath);
    }
}

4.布局

<?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">

    <Button
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="选择图片"
        android:id="@+id/get_image"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/width"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toBottomOf="@id/get_image"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@id/height"
        android:hint="输入宽度"/>

    <EditText
        android:id="@+id/height"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toBottomOf="@id/get_image"
        app:layout_constraintLeft_toRightOf="@id/width"
       app:layout_constraintRight_toRightOf="parent"
        android:hint="输入高度"/>

    <Button
        android:id="@+id/show"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@id/height"
        android:text="生成"/>

    <ImageView
        android:id="@+id/image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@id/show"
        app:layout_constraintBottom_toBottomOf="parent"/>

</android.support.constraint.ConstraintLayout>

5.权限

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

图片二次采样///////////子线程

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