在Android应用程序的理解内存泄漏 [英] Understanding memory leaks in Android application

问题描述

我发现文中的避免内存泄漏，它是说，以下code：

I found the article "Avoiding memory leaks", where it is said that the following code:

private static Drawable sBackground;

@Override
protected void onCreate(Bundle state) {
  super.onCreate(state);

  TextView label = new TextView(this);
  label.setText("Leaks are bad");

  if (sBackground == null) {
    sBackground = getDrawable(R.drawable.large_bitmap);
  }
  label.setBackgroundDrawable(sBackground);

  setContentView(label);
}

是不是一个好主意，因为：

is not a good idea, since:

在屏幕的方向改变，系统会默认情况下，
  销毁当前活动，并创建一个新的，而preserving其
  州。在这样做时，机器人将从重新加载应用程序的UI
  资源。

When the screen orientation changes the system will, by default, destroy the current activity and create a new one while preserving its state. In doing so, Android will reload the application's UI from the resources.

所以上面的code：

...泄漏在第一屏幕方向变化所造成的第一个活动。当被拉伸附连到一个视图，该视图是
  设置为上绘制一个回调。在上面，这个code片段
  装置可绘有其本身具有的TextView的一个参考
  参考活动（上下文），这反过来有引用
  以pretty任何东西（取决于您的code）

...leaks the first activity created upon the first screen orientation change. When a Drawable is attached to a view, the view is set as a callback on the drawable. In the code snippet above, this means the drawable has a reference to the TextView which itself has a reference to the activity (the Context) which in turns has references to pretty much anything (depending on your code.)

但是，当屏幕方向的变化，该方法<一个href=\"http://grep$c$c.com/file/repository.grep$c$c.com/java/ext/com.google.android/android/4.4.3_r1/android/view/View.java#View.setBackgroundDrawable%28android.graphics.drawable.Drawable%29\"相对=nofollow> setBackgroundDrawable（可绘制背景）被调用，这反过来又要求：

But, when screen orientation changes, the method setBackgroundDrawable(Drawable background) is called, which in turn calls:

background.setCallback(this);

该方法 Drawable.setCallback（）通过以下方式definied：

The method Drawable.setCallback() is definied in the following way:

public final void setCallback(Callback cb) {
    mCallback = new WeakReference<Callback>(cb);
}

所以，现在背景应该释放旧参考previous TextView的，以及一个新的参考到新的TextView应创建。

So, now background should release the old reference to the previous TextView, and a new reference to the new TextView should be created.

所以，这似乎是改变屏幕的方向泄漏只有等到活动是新创建的一个参考。

So, it seems like changing screen orientation leaks a reference only until the activity is newly created.

我在哪里去了？

推荐答案

您是绝对正确的。然而，有一个微妙的一点：本文是从的 2010 的。当时， setCallback 的实施是<一个href=\"http://grep$c$c.com/file_/repository.grep$c$c.com/java/ext/com.google.android/android/4.0.1_r1/android/graphics/drawable/Drawable.java/?v=diff&id2=2.3.7_r1#325\"相对=nofollow>不同：

You are absolutely right. However, there is one subtle point: the article is from 2009. Back then, the implementation of setCallback was different:

Android和LT = 2.3.7：

public final void setCallback(Callback cb) {
    mCallback = cb;
}

Android的> = 4.0.1：

public final void setCallback(Callback cb) {
    mCallback = new WeakReference<Callback>(cb);
}

<子> grep的code显示中间版本的没有源$ C ​​$ C，这是唯一的差异我能很快找到。

所以，再次，你在这种特殊情况下绝对正确（如果你的目标> 14即是）。然而，它仍然是真正思考什么是真​​正发生非常重要的，当你保持一个静态引用这些项目（像你这样）。有众多的情况下，你肯定能泄漏上下文。

So, again, you're absolutely right in this specific case (if you're targeting >14 that is). However, it is still very important to really think about what is actually happening when you keep a static reference to such items (like you did). There are numerous cases where you certainly could be leaking the Context.

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