How to Solve Error: You need to use a Theme.AppCompat theme (or descendant) with this activity.

When learning the activity life cycle, I hope to test the difference between onPause() and onStop() through the Dialog theme. When clicking the button to jump to the Activity, an error is reported:

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)

Find the most useful sentence, indicating that the theme used does not match the current Activity:

You need to use a Theme.AppCompat theme (or descendant) with this activity.

The activity configuration in AndroidManifest.xml is as follows:

1 <activity
2     android:name=".DialogActivity"
3     android:theme="@android:style/Theme.Dialog">
4 </activity>

Change the theme to AppCompat according to the error message:

1 <activity
2     android:name=".DialogActivity"
3     android:theme="@style/Theme.AppCompat.Dialog">
4 </activity>

After checking the java code, I found that my Activity inherits the AppCompatActivity class. When creating an Activity in Android Studio, if you check the Backwards Compatibility (AppCompat) option, the created Activity will inherit AppCompatActivity instead of Activity, and you need to use the corresponding AppCompat theme.

java code:

 1 import android.support.v7.app.AppCompatActivity;
 2 import android.os.Bundle;
 3 
 4 public class DialogActivity extends AppCompatActivity {
 5 
 6     @Override
 7     protected void onCreate(Bundle savedInstanceState) {
 8         super.onCreate(savedInstanceState);
 9         setContentView(R.layout.activity_dialog);
10     }
11 
12 }


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