Activity 中的 onPause() 和 onStop() [英] onPause() and onStop() in Activity

问题描述

我是 Android 开发新手，但仍然无法理解活动中的 onPause() 和 onStop() 方法.

I am new to Android development and I am still not able to understand the onPause() and onStop() methods in an activity.

在我的应用程序中，我有一个名为 Counter 的静态类，它将变量的状态保存在应用程序的内存中.我的应用程序在模拟器中运行良好.我试图测试的是 onPause() 与 onStop() 的不同行为.

In my app, I have a static class that I name Counter, and it keeps the state of variables in memory for the app. My app runs fine in the emulator. What I was trying to test was differential behavior of onPause() versus onStop().

对于 onPause，我希望保留存储在 Counter 类成员中的值，而调用 onStop() 我希望将计数器值重置为零.所以我重写了 onStop() 并将计数器类中的变量设置为零.但是，在模拟器中，我似乎无法让应用程序处于暂停状态.在模拟器中，我打开我的应用程序，练习它.然后我点击模拟器的主页按钮(不是返回按钮)，并启动另一个应用程序，相信这会模仿 onPause() 活动.但是，模拟器似乎不支持这一点(我使用的是 armeabi v7a 模拟器)，它似乎总是在调用 onStop() 因为我的计数器值都回到零，根据我的覆盖onStop().这是模拟器固有的还是我做错了什么让我的活动进入暂停状态?

For onPause, I wanted the values stored in the Counter class's members retained, whereas calling onStop() I wanted the counter values reset to zero. So I override onStop() and set the variables inside the counter class to zero. However, in the emulator, I cannot seem to get the app in the Paused state. In the emulator, I open my app, exercise it. Then I hit the home button (not the back button) of the emulator, and launch another app, believing that this would mimic onPause() activity. However, the emulator does not appear to honor this (I am using an armeabi v7a emulator), it seems to always be calling onStop() because my counter values all go back to zero, per my override in onStop(). Is this inherent to the emulator or am I doing something wrong to get my activity into the paused state?

推荐答案

我不确定您正在使用哪个模拟器进行测试，但 onPause 是一种始终em> 保证在您的 Activity 失去焦点时被调用(我说 always 因为在某些设备上，特别是那些运行 Android 3.2+ 的设备上，onStop并不总是保证在 Activity 被销毁之前被调用).

I'm not sure which emulator you are testing with, but onPause is the one method that is always guaranteed to be called when your Activity loses focus (and I say always because on some devices, specifically those running Android 3.2+, onStop is not always guaranteed to be called before the Activity is destroyed).

对于初学者来说，了解 Activity 生命周期的一个好方法是用 Log 乱扔你的重写方法.例如:

A nice way to understand the Activity lifecycle for beginners is to litter your overriden methods with Logs. For example:

public class SampleActivity extends Activity {

    /**
     * A string constant to use in calls to the "log" methods. Its
     * value is often given by the name of the class, as this will 
     * allow you to easily determine where log methods are coming
     * from when you analyze your logcat output.
     */
    private static final String TAG = "SampleActivity";

    /**
     * Toggle this boolean constant's value to turn on/off logging
     * within the class. 
     */
    private static final boolean VERBOSE = true;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (VERBOSE) Log.v(TAG, "+++ ON CREATE +++");
    }

    @Override
    public void onStart() {
        super.onStart();
        if (VERBOSE) Log.v(TAG, "++ ON START ++");
    }

   @Override
    public void onResume() {
        super.onResume();
        if (VERBOSE) Log.v(TAG, "+ ON RESUME +");
    }

    @Override
    public void onPause() {
        super.onPause();
        if (VERBOSE) Log.v(TAG, "- ON PAUSE -");
    }

    @Override
    public void onStop() {
        super.onStop();
        if (VERBOSE) Log.v(TAG, "-- ON STOP --");
    }

   @Override
    public void onDestroy() {
        super.onDestroy();
        if (VERBOSE) Log.v(TAG, "- ON DESTROY -");
    }
}

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