今天写android实验碰到到一个问题，在用AlertDialog.Builder类构建一个对话框之后，调用Builder.show()方法时抛出异常如下：
06-16 21:52:16.456 5017-5017/xyz.qlrr.sqliteapp W/System.err: java.lang.IllegalStateException: You need to use a Theme.AppCompat theme (or descendant) with this activity. 06-16 21:52:16.457 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.support.v7.app.AppCompatDelegateImplV9.createSubDecor(AppCompatDelegateImplV9.java:359) 06-16 21:52:16.457 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.support.v7.app.AppCompatDelegateImplV9.ensureSubDecor(AppCompatDelegateImplV9.java:328) 06-16 21:52:16.457 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:289) 06-16 21:52:16.457 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.support.v7.app.AppCompatDialog.setContentView(AppCompatDialog.java:83) 06-16 21:52:16.457 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.support.v7.app.AlertController.installContent(AlertController.java:225) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.support.v7.app.AlertDialog.onCreate(AlertDialog.java:257) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.app.Dialog.dispatchOnCreate(Dialog.java:471) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.app.Dialog.show(Dialog.java:334) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.support.v7.app.AlertDialog$Builder.show(AlertDialog.java:955) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at xyz.qlrr.sqliteapp.DisplayActivity.onItemClick(DisplayActivity.java:76) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.widget.AdapterView.performItemClick(AdapterView.java:310) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.widget.AbsListView.performItemClick(AbsListView.java:1187) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.widget.AbsListView$PerformClick.run(AbsListView.java:3108) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.widget.AbsListView.onTouchUp(AbsListView.java:4099) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.widget.AbsListView.onTouchEvent(AbsListView.java:3781) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.View.dispatchTouchEvent(View.java:9328) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2564) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2250) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2570) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2264) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2570) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2264) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2570) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2264) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2570) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2264) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2570) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2264) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2570) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2264) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at com.android.internal.policy.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2452) 06-16 21:52:16.458 5017-5017/xyz.qlrr.sqliteapp W/System.err: at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1749) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.app.Activity.dispatchTouchEvent(Activity.java:2927) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:71) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:71) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at com.android.internal.policy.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2405) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.View.dispatchPointerEvent(View.java:9548) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4515) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4313) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3823) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3883) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3842) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3990) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3850) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4047) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3823) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3883) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3842) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3850) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3823) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6239) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6213) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6174) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:6346) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.ViewRootImpl$ColorWindowInputEventReceiver.onInputEvent(ViewRootImpl.java:7597) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185) 06-16 21:52:16.459 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.os.MessageQueue.nativePollOnce(Native Method) 06-16 21:52:16.460 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.os.MessageQueue.next(MessageQueue.java:323) 06-16 21:52:16.460 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.os.Looper.loop(Looper.java:163) 06-16 21:52:16.460 5017-5017/xyz.qlrr.sqliteapp W/System.err: at android.app.ActivityThread.main(ActivityThread.java:5769) 06-16 21:52:16.460 5017-5017/xyz.qlrr.sqliteapp W/System.err: at java.lang.reflect.Method.invoke(Native Method) 06-16 21:52:16.460 5017-5017/xyz.qlrr.sqliteapp W/System.err: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 06-16 21:52:16.460 5017-5017/xyz.qlrr.sqliteapp W/System.err: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:674)
上网百度查找答案说是因为活动是继承了android.support.v7.app.AppCompatActivity，而且主题设置为了和这个活动父类不兼容的主题。我查看代码不是这个原因。后来发现在创建AlertDialog.Builder()的使用调用的上下文是用getApplicationContext()方法获取的，将上下文改为当前的活动对象this问题就解决了。
修改前：
1 AlertDialog.Builder builder = new AlertDialog.Builder(getApplicationContext()); 2 builder.setMessage("确认").setMessage("您确定要删除这条记录吗？"); 3 builder.setNegativeButton("确定", new DialogInterface.OnClickListener() { 4 @Override 5 public void onClick(DialogInterface dialogInterface, int i) { 6 TextView idView = (TextView) view.findViewById(R.id.idView); 7 String s = idView.getText().toString(); 8 Integer id = Integer.valueOf(s); 9 SQLiteHelper sqLiteHelper = new SQLiteHelper(getApplicationContext()); 10 boolean b = sqLiteHelper.delete(id); 11 Toast.makeText(DisplayActivity.this,b?"删除成功":"删除失败",Toast.LENGTH_SHORT).show(); 12 if(b){ 13 loadlistview(); 14 } 15 } 16 }); 17 builder.setPositiveButton("取消",null); 18 builder.show();
修改后：
AlertDialog.Builder builder = new AlertDialog.Builder(this); builder.setMessage("确认").setMessage("您确定要删除这条记录吗？"); builder.setNegativeButton("确定", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialogInterface, int i) { TextView idView = (TextView) view.findViewById(R.id.idView); String s = idView.getText().toString(); Integer id = Integer.valueOf(s); SQLiteHelper sqLiteHelper = new SQLiteHelper(getApplicationContext()); boolean b = sqLiteHelper.delete(id); Toast.makeText(DisplayActivity.this,b?"删除成功":"删除失败",Toast.LENGTH_SHORT).show(); if(b){ loadlistview(); } } }); builder.setPositiveButton("取消",null); builder.show();