Android 使用LeakCanary检测内存泄漏，分析原因

内存泄漏是指无用对象（不再使用的对象）持续占有内存或无用对象的内存得不到及时释放，从而造成内存空间的浪费称为内存泄漏。

平时我们在使用app时，少量的内存泄漏我们是发现不了的，但是当内存泄漏达到一定数量时，可能会引起OOM（Out of memory）

我们可以借助工具LeakCanary来检测内测泄漏

首先在项目build.gradle中引入LeakCanary库

  //https://github.com/square/leakcanary 内存泄漏分析工具（debugImplementation 来配置依赖，只在开发环境中依赖）debugImplementation 'com.squareup.leakcanary:leakcanary-android:2.12'

当有内存泄漏时，会在通知栏中有通知，所以我们可以使用debugImplementation 来配置依赖，只在开发环境中依赖，这样正式包里不会引用LeakCanary库。

使用LeakCanary 2.0以上版本，无需做任何配置，引入库后就会自动检测内存泄漏

单例模式导致的内存泄漏

创建一个单例

public class Singleton {private static Singleton sInstance;private Context mContext;private Singleton(Context context) {this.mContext = context;}public static Singleton getInstance(Context context) {if (sInstance == null) {sInstance = new Singleton(context);}return sInstance;}public void test(){mContext.getContentResolver();}
}

在Activity中执行

public class TestLeakActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_test_leak);Singleton.getInstance(this).test();}
}

执行完单例之后看一下leakcanary

LeakCanary: 1 APPLICATION LEAKS
LeakCanary: ┬───
LeakCanary: │ GC Root: Local variable in native code
LeakCanary: │ ...            
LeakCanary: ├─ com.example.myapplication.Singleton instance
LeakCanary: │    Leaking: UNKNOWN
LeakCanary: │    Retaining 112915 bytes in 1674 objects
LeakCanary: │    mContext instance of com.example.myapplication.TestLeakActivity with mDestroyed = true
LeakCanary: │    ↓ Singleton.mContext
LeakCanary: │                ~~~~~~~~
LeakCanary: ╰→ com.example.myapplication.TestLeakActivity instance
LeakCanary: ​     Leaking: YES (ObjectWatcher was watching this because com.example.myapplication.TestLeakActivity received
LeakCanary: ​     Activity#onDestroy() callback and Activity#mDestroyed is true)
LeakCanary: ​     Retaining 112903 bytes in 1673 objects
LeakCanary: ​     key = 297d72a4-5e9d-41bf-baba-6856105c73f0
LeakCanary: ​     watchDurationMillis = 5176
LeakCanary: ​     retainedDurationMillis = 139
LeakCanary: ​     mApplication instance of com.example.myapplication.MyApplication
LeakCanary: ​     mBase instance of android.app.ContextImpl, not wrapping known Android context
LeakCanary: ====================================
LeakCanary: 0 LIBRARY LEAKS

发现UNKNOW 出现地方为Singleton中的mContext，说明当前的mContext可能没有释放掉，但是后续又看到YES说明当前确实没有释放掉

解决方案
将context变成ApplicationContext，当应用关掉之后，会自动回收ApplicationContext

 private Singleton(Context context) {this.mContext = context.getApplicationContext();}