memory optimization

One way to get the phone memory:

ActivityManager activityManager = (ActivityManager)getSystemService(Context.ACTIVITY_SERVICE);

int memClass = activityManager.getMemoryClass();

int largeMemClass = activityManager.getLargeMemoryClass();

Get the memory status of the phone when it is running:

float totalMemory = Runtime.getRuntime().totalMemory()/(1024*1024);

float freeMemory = Runtime.getRuntime().freeMemory()/(1024*1024);

float maxmemory = Runtime.getRuntime (). maxMemory / （1024 * 1024）;

adb shell to enter the bottom layer of the device

ps to view all processes

dumpsys meminfo + package name to view the detailed stack information of a specific process

An app is usually a process corresponding to a virtual machine

GC only triggers garbage collection when the remaining space in the Heap is insufficient

When GC is triggered, all threads will be suspended

APP memory limit mechanism

The maximum memory limit allocated per app, which varies by device

Big memory eaters: pictures

Data structure optimization:

StringBuilder for frequent string concatenation

ArrayMap SparseArray替换HashMap

Memory thrashing (variables are created frequently and quickly discarded) causes frequent GCs

object reuse

Reuse the resources that come with the system

ConvertView reuse of ListView/GridView

Avoid performing object creation in the onDraw method

Memory leak : Due to code flaws, although this piece of memory has stopped being used, it is still referenced by other things. Yes, the GC cannot reclaim it.

Memory leaks will lead to less and less remaining available heap and frequent GC

Use Application Context instead of Activity Context

注意Cursor对象是否及时关闭

OOM问题优化方法

注意临时BItmap对象的及时回收

避免Bitmap的浪费

加载Bitmap:缩放比例，解码格式，局部加载

示例如下：

package com.example.admin.myapplication.oom;

import android.content.Intent;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapRegionDecoder;
import android.graphics.Rect;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;
import android.support.v7.app.AppCompatActivity;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

import com.example.admin.myapplication.R;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;

public class OOMActivity extends AppCompatActivity {

    private ImageView img;
    private Bitmap bitmap;
    private File file = null;
    private int SCREEN_WIDTH, SCREEN_HEIGHT;
    private int shifpx = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
         img = (ImageView) findViewById(R.id.img);
        DisplayMetrics dm = new DisplayMetrics();
        dm = this.getResources().getDisplayMetrics();
        SCREEN_WIDTH = dm.widthPixels;
        SCREEN_HEIGHT = dm.heightPixels;
        Log.e("oomactivity","screen_width:"+SCREEN_WIDTH);

        Button button = (Button) findViewById(R.id.choosepic);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                getPic();
            }
        });

        findViewById(R.id.picpoti).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                changePicOopti();
            }
        });
        findViewById(R.id.changergb).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                changeRGB();
            }
        });
        findViewById(R.id.partload).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                partLoad();
            }
        });
        findViewById(R.id.movepart).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                shifpx++;
                partLoad();
            }
        });


    }

    private void getPic(){
        Intent intent = new Intent(Intent.ACTION_PICK,
                android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
        startActivityForResult(intent, 1);
//        String path = "/storage/emulated/0/qingming.jpg";
//        bitmap = BitmapFactory.decodeResource(getResources(),R.drawable.qingming);
//        img.setImageBitmap(bitmap);
//        Log.e("oomActivity","bitmap.length:"+bitmap.getByteCount());
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {

        try{
            String path = getRealPathFromURI(data.getData());
            file = new File(path);
            if (file == null) return;
            if (file.length()==0){
                file .delete();
                return;
            }
            Log.e("oomActivity","file;"+file.getName()+" ,length:"+file.length());
            FileInputStream fin = new FileInputStream(file);
            bitmap = BitmapFactory.decodeStream(fin);
            Log.e("oomActivity","bitmap.lenght:"+bitmap.getByteCount());

            Bitmap bitmap1 = BitmapFactory.decodeFile(path);
            Log.e("oomActivity","bitmap1.lenght:+"+bitmap1.getByteCount());
            img.setImageBitmap(bitmap);

        }catch(Exception e){
            e.printStackTrace();
            Log.e("oomActivity",e.toString());
        }
    }

    /**
     *缩放
     */
    private void changePicOopti(){
        Log.e("oomActivity","---------------------------------------------");
        if (file==null){
            return;
        }
        try{

            BitmapFactory.Options options= new BitmapFactory.Options();
            options.inJustDecodeBounds = true;
            BitmapFactory.decodeStream(new FileInputStream(file),null,options);
            int width_tem = options.outWidth,height_tmp = options.outHeight;
            int scale = 2;
            while(true){
                if (width_tem/scale<SCREEN_WIDTH){
                    break;

                }
                scale+=2;
            }
            scale=4;
            BitmapFactory.Options options1 = new BitmapFactory.Options();
            options1.inSampleSize= scale;
            Log.e("oomActivity","bitmap.scale:"+scale);
            FileInputStream fileInputStream = new FileInputStream(file);
            bitmap = BitmapFactory.decodeStream(fileInputStream,null,options1);
            Log.e("oomActivity","scale_bitmap.length:"+bitmap.getByteCount());
            img.setImageBitmap(bitmap);

        }catch (Exception e){
            e.printStackTrace();
        }

    }

    /**
     * 改变RGB
     */
    private void changeRGB(){
        Log.e("oomActivity","---------------------------------------------");
        if (file != null){
            BitmapFactory.Options options = new BitmapFactory.Options();
            options.inPreferredConfig =Bitmap.Config.RGB_565;
            try {
                FileInputStream fileInputStream = new FileInputStream(file);
                bitmap = BitmapFactory.decodeStream(fileInputStream,null,options);
                Log.e("oomActivity","RGB+565_bitmap.length"+ bitmap.getByteCount());
                img.setImageBitmap(bitmap);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
                Log.e("oomActivity",""+e.toString());
            }

        }
    }

    /**
     * 局部显示
     */
    private void partLoad(){

        if (file==null)
            return;

        try{
            FileInputStream fileInputStream = new FileInputStream(file);
            BitmapFactory.Options options = new BitmapFactory.Options();
            BitmapFactory.decodeStream(fileInputStream,null,options);
            int widht = options.outWidth;
            int height = options.outHeight;


            //设置显示图片的中心区域
            fileInputStream = new FileInputStream(file);
            BitmapRegionDecoder bitmapRegionDecoder = BitmapRegionDecoder.newInstance(fileInputStream,false);
            BitmapFactory.Options options1 = new BitmapFactory.Options();
            bitmap = bitmapRegionDecoder.decodeRegion(new Rect(widht/2-SCREEN_WIDTH/2+shifpx,height/2-SCREEN_HEIGHT/2,widht/2+SCREEN_WIDTH/2+shifpx,height/2+SCREEN_HEIGHT/2),options);
            img.setImageBitmap(bitmap);
        }catch(Exception e){

        }
    }


    public String getRealPathFromURI(Uri contentUri){
        String res = null;
        String proj = (MediaStore.Images.Media.DATA);
        Cursor cursor = this.getContentResolver().query(contentUri, new String[]{proj},null,null,null);
        if (cursor.moveToFirst()){
            int column_index = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
            res = cursor.getString((column_index));
        }
        cursor.close();
        return res;
    }

}