学习 Activity 生命周期时希望通过 Dialog 主题测试 onPause() 和 onStop() 的区别，点击按钮跳转 Activity 时报错：
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.activitylifecycletest, PID: 2920
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.activitylifecycletest/com.example.activitylifecycletest.DialogActivity}: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity.
at android.support.v7.app.AppCompatDelegateImplV9.createSubDecor(AppCompatDelegateImplV9.java:347)
at android.support.v7.app.AppCompatDelegateImplV9.ensureSubDecor(AppCompatDelegateImplV9.java:316)
at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:281)
at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140)
at com.example.activitylifecycletest.DialogActivity.onCreate(DialogActivity.java:11)
at android.app.Activity.performCreate(Activity.java:6664)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
找到最有用的一句话，说明所使用的 theme 和当前 Activity 不匹配：
You need to use a Theme.AppCompat theme (or descendant) with this activity.
AndroidManifest.xml 中 activity 配置如下：
<activity
android:name=".DialogActivity"
android:theme="@android:style/Theme.Dialog">
</activity>
根据报错提示改为 AppCompat 主题即可：
<activity
android:name=".DialogActivity"
android:theme="@style/Theme.AppCompat.Dialog">
</activity>
查看 java 代码后发现我的 Activity 继承 AppCompatActivity 类。在 Android Studio 中创建 Activity 时，如果勾选了 Backwards Compatibility(AppCompat) 选项，所创建的 Activity 会继承 AppCompatActivity 而不是 Activity，此时需要使用对应的 AppCompat 主题。
java 代码：
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle; public class DialogActivity extends AppCompatActivity { @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_dialog);
} }