java - 了解 Android 应用程序中的内存泄漏

Question

我找到了这篇文章 "Avoiding memory leaks" ，据说下面的代码:

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);
}

这不是一个好主意，因为:

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.

所以上面的代码:

...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，当屏幕方向改变时，方法setBackgroundDrawable(Drawable background)被调用，它又调用:

background.setCallback(this);

Drawable.setCallback() 方法定义如下:

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

因此，现在后台应该释放对先前 TextView 的旧引用，并且应该创建对新 TextView 的新引用。

因此，更改屏幕方向似乎只会在新创建 Activity 之前泄漏引用。

我哪里错了？

Answer 1

你完全正确。但是，有一点很微妙:这篇文章是 2009 的。那时，setCallback 的实现是 different :

Android <= 2.3.7:

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

Android >= 4.0.1:

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

_{Grepcode 没有显示中间版本的源代码，这是我能快速找到的唯一差异。}

---

所以，再说一次，在这个特定情况下，您是绝对正确的(如果您的目标是 >14)。但是，当您保持对此类项目的静态引用(就像您所做的那样)时，真正考虑实际发生的事情仍然非常重要。在许多情况下，您肯定会泄露 Context。