AndroidStudio中Handler类的内存溢出风险

Posted 2020-12-28 King

package com.test.king.xmlparser;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.res.Resources;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.TextView;

import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;

import java.io.IOException;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    private static TextView tvContent;
    private static final int MSG_FINISH=0x0001;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tvContent=findViewById(R.id.tv_content);

    }

    //内部类解决可能存在的内存溢出
    /*
    *、本文描述静态和非静态内部类的区别是非静态内部类持有外部类的引用。
2、内部类实例的持有对象的生命周期大于其外部类对象，那么就有可能导致内存泄露。
比如,要实例化一个超出activity生命周期的内部类对象，
避免使用非静态的内部类。建议使用静态内部类并且在内部类中持有外部类的弱引用。
    *
    * */
    //静态内部类
    private static class MyHandler extends Handler {
        private final WeakReference<MainActivity> mActivity;
        //构造方法
        public MyHandler(MainActivity activity) {
            mActivity = new WeakReference<MainActivity>(activity);//对外部类的弱引用
        }
        @Override
        public void handleMessage(Message msg) {
            MainActivity activity = mActivity.get();
            if (activity != null) {
                switch (msg.what)
                {
                    case MSG_FINISH:
                        List<String> contents=(List<String>)msg.obj;
                        //在主线程中显示
                        for(String content:contents)
                        {
                            tvContent.append(content+"
");
                        }
                        break;
                }
            }
        }
    }
    //new Handler对象处理消息，下文有引用
    private final MyHandler mHandler = new MyHandler(this);
    //警告
    /*
    private Handler handler=new Handler()
    {
        @Override
        //重写handleMessage方法处理消息
        public void handleMessage(Message msg) {
            switch (msg.what)
            {
                case MSG_FINISH:
                    List<String> contents=(List<String>)msg.obj;
                    //在主线程中显示
                    for(String content:contents)
                    {
                        tvContent.append(content+"
");
                    }
                    break;
            }

        }
    };*/


    public  void parser(View view) throws IOException, XmlPullParserException {
     //常规方法
     /*
     List<String> contents=getPullParserContent(getResources(),R.xml.words);
     for(String content:contents)
     {
         tvContent.append(content+"
");
     }*/
     //解析XML可能需要耗费很长的时间，所以这里单独做一个子线程
        new Thread()
        {
            @Override
            //重写run方法
            public void run()
            {
                try {
                    List<String> contents=getPullParserContent(getResources(),R.xml.words);
                    //完成工作，通知主线程
                    Message msg=mHandler.obtainMessage();//也可以new Message
                    msg.what=MSG_FINISH;
                    msg.obj=contents;
                    mHandler.sendMessage(msg);
                } catch (IOException e) {
                    e.printStackTrace();
                } catch (XmlPullParserException e) {
                    e.printStackTrace();
                }
            }
        }.start();

    }
    private List<String> getPullParserContent(Resources res,int id) throws IOException, XmlPullParserException {
        List<String> contents = null;
        String tagName;
        //XmlPullParser
        XmlPullParser parser = res.getXml(id);
        //Pull解析本质是SAX解析
        int eventType = parser.getEventType();
        while (eventType != XmlPullParser.END_DOCUMENT) {
            switch (eventType) {
                case XmlPullParser.START_DOCUMENT:
                    Log.i("Test", "START_DOCUMENT");
                    contents=new ArrayList<String>();
                    break;
                case XmlPullParser.END_DOCUMENT:
                    break;
                case XmlPullParser.START_TAG:
                    tagName = parser.getName();
                    if (tagName.equals("word")) {
                        String value = parser.getAttributeValue(0);
                        contents.add(value);
                        Log.i("Test", "START_TAG:" + tagName + " " + value);
                    }
                    break;
                case XmlPullParser.END_TAG:
                    tagName = parser.getName();
                    Log.i("Test", "END_TAG:" + tagName);
                    break;
            }
            eventType = parser.next();
        }
        return contents;
    }
}