如何更新Android应用程序时，清除旧preferences？ [英] How to clear old preferences when updating Android app?

问题描述

我有谷歌播放市场上的应用程序。对于我不会打扰进入种种原因，我已经改变了我的一些preferences类型。例如，一个preference类型是一个整数，并在最近的版本，它现在是一个字符串。我想这是不好的做法，但不幸的是我不得不这样做。

I have an app on the Google Play market. For various reasons that I won't bother going into, I have changed the type of some of my preferences. For example a preference type was an Integer and in the most recent version it is now a String. I imagine this isn't good practice but unfortunately I had to do it.

我担心的是，当有人更新到新版本的应用程序将崩溃为preference类型发生了变化。出于这个原因，我想清楚，每当应用程序更新时，preferences（我又意识到不理想！）

My concern is that when someone updates to the new version their app will crash as the preference types have changed. For this reason I would like to clear the preferences whenever the app is updated (again I realise not ideal!)

这可能吗？

推荐答案

在共享preferences.Editor 类有一个明确（） 函数，什么删除所有存储的preferences（后提交（））。你可以创建一个布尔标志，将显示是否有更新的需要：

The SharedPreferences.Editor class has a clear() function, what removes all your stored preferences (after a commit()). You could create a boolean flag which will indicate if updated needed:

void updatePreferences() {
    SharedPreferences prefs = ...;
    if(prefs.getBoolean("update_required", true)) {
        SharedPreferences.Editor editor = prefs.edit();
        editor.clear();

        /*....make the updates....*/

        editor.putBoolean("update_required", false)
        editor.commit();
    }
}

在这之后，你需要调用这个在你的主（第一个开始）的活动，您可以访问任何preferenes之前。

And after that you need to call this in your main (first starting) activity, before you access any preferenes.

修改

要获得最新的版本（清单中所声明的版本code）：

To get the current version (The versionCode declared in the manifest):

int version = 1;
try {
    version = getPackageManager().getPackageInfo(getPackageName(), 0).versionCode;
} catch (NameNotFoundException e) {
    e.printStackTrace();
}

if(version > ...) {
    //do something
}

修改

如果你想要做一些更新操作，每当版本变动，那么你可以做这样的事情：

If you want to do some updating operation, whenever the version changes, then you can do something like this:

void runUpdatesIfNecessary() {
    int versionCode = getPackageManager().getPackageInfo(getPackageName(), 0).versionCode;
    SharedPreferences prefs = ...;
    if (prefs.getInt("lastUpdate", 0) != versionCode) {
        try {
            runUpddates();

            // Commiting in the preferences, that the update was successful.
            SharedPreferences.Editor editor = prefs.edit();
            editor.putInt("lastUpdate", versionCode);
            editor.commit();
        } catch(Throwable t) {
            // update failed, or cancelled
        }
    }
}

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