Android setTheme无效的问题 (轉自：http://endf.javaeye.com/blog/771685)

在SDK中介绍setTheme需要在setContentView之前使用，但是在实际使用中发现只有在super.onCreate调用之前调用方可有效，也许是2.2的一个问题。可以参照
http://code.google.com/p/android/issues/detail?id=4394
这一部分内容
其中下边这个人的回答很有参考价值

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Hey Christian,

if you just need a dynamic (same activity to be either a dialog or a full screen
activity) you could try the following approach.

AndroidManifest.xml
<activity android:name=".ShowSettingsActivity"
  ...
  android:theme="@android:style/Theme.Dialog">
  ...

ShowSettingsActivity.java
@Override public void setTheme(int resid) {
   boolean isFullScreen = ... ; // get from configuration
   super.setTheme(isFullScreen ? android.R.style.Theme : resid);
}

Now you just need to define isFullScreen and restart activity. This approach works
with my application (market://search?q=pname:com.bwx.bequick). Hope this helps.

Best Regards,
Sergey

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上边这个方法中有一个关键的参数就是isFullScreen这个值，这个值需要在onCreate调用之前就设置好方可有效，因为在 activity framework中会根据androidmanifest.xml文件的theme是否存在进行第一次设置，而后就没有办法改变了（这应该是一个 bug）。