Handler防治內存泄漏的優化使用方法
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一.爲什麼進行優化:
在使用handler時,有時候我們會傳遞參數,這些參數可能是對某個已經銷燬的Activity的引用。從而導致系統不能GC掉這個Activity導致資源浪費。其根本原因是靜態內部類持有了外部類的引用,導致外部activity無法被回收。
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二.怎麼優化:
1.將handler設置爲靜態
2.傳遞參數時傳遞弱引用而不是強引用
3.在創建handler的activity中的onDestory回調方法裏,加入handler的釋放方法:handler.removeCallBack()
案例:
倒計時程序
佈局文件:
<?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">
<TextView
android:id="@+id/text1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
java文件:
package com.example.handlerest;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.widget.TextView;
import java.lang.ref.WeakReference;
public class MainActivity extends AppCompatActivity {
public static final int COUNTDOWN = 1001;
public static final int MAX_NUMBER = 10;
public static final int DELAY_MILLIS = 1000;
private TextView textView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView= findViewById(R.id.text1);
CountDownHandler handler = new CountDownHandler(this);
Message message = Message.obtain();
message.what = COUNTDOWN;
message.arg1 = MAX_NUMBER;
handler.sendMessageDelayed(message,DELAY_MILLIS);
}
public static class CountDownHandler extends Handler
{
final WeakReference<MainActivity> mweakReference;//定義對MainActivity的弱引用
public CountDownHandler(MainActivity activity) {
mweakReference = new WeakReference<>(activity);
}
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
MainActivity mainActivity = mweakReference.get();//取得對MainActivity的引用
switch (msg.what)
{
case COUNTDOWN:
{
int value = msg.arg1;
if(value>=0)
{
mainActivity.textView.setText(String.valueOf(value--));
Message message = Message.obtain();//msg不能複用,必須重新從消息池中獲得實例
message.what = COUNTDOWN;
message.arg1=value;
sendMessageDelayed(message, DELAY_MILLIS);
}
break;
}
}
}
}
}