我有一个Android应用程序，用户可以在其中同时使用String修改多个EditText项目，因此我需要弄清楚发生了什么更改，以便将更改通知服务器(创建新项目，更新现有项目或删除后者) )，这就是为什么我将DiffUtil与ListUpdateCallback一起使用的原因。如果旧列表的大小为2，则该问题；我删除了索引0处的项目，然后将3个项目添加到列表的末尾，我收到了onInserted的回调，其位置参数不正确导致IndexOutOfBoundsException，(这是删除旧列表中任何项目的行为，除了对于最后一个)，请查看此GIF that shows the problem。
我尝试了以下代码，并对新列表进行了其他更改，例如从索引1处删除，然后将3个项目添加到列表的末尾，效果很好!
我正在使用的数组的类型为Answer，它是一个类:
public class Answer {
private String id;
private String questionId;
private String text;
private Integer count;
}
请注意，如果两个项目相同，则ID可以标识2个不同的对象；然后可以通过文本识别内容。
DiffUtil.Callback
public class AnswersDiffCallback extends DiffUtil.Callback {
List<Answer> newAnswers;
List<Answer> oldAnswers;
public AnswersDiffCallback(List<Answer> newAnswers, List<Answer> oldAnswers) {
this.newAnswers = newAnswers;
this.oldAnswers = oldAnswers;
}
@Override
public int getOldListSize() {
return oldAnswers == null ? 0 : oldAnswers.size();
}
@Override
public int getNewListSize() {
return newAnswers == null ? 0 : newAnswers.size();
}
@Override
public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
Answer oldAnswer = oldAnswers.get(oldItemPosition);
Answer newAnswer = newAnswers.get(newItemPosition);
return Objects.equals(oldAnswer.getId(), newAnswer.getId());
}
@Override
public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
Answer oldAnswer = oldAnswers.get(oldItemPosition);
Answer newAnswer = newAnswers.get(newItemPosition);
return Objects.equals(oldAnswer.getText(), newAnswer.getText());
}
}
在ListUpdateCallback中，我尝试记录获取的回调，以便在与服务器对话之前测试其是否正常工作。
Log.d(TAG, "answers: oldAnswers = " + Utils.serializeObject(oldAnswers));
Log.d(TAG, "answers: newAnswers = " + Utils.serializeObject(newAnswers));
Log.d(TAG, "-----------------------------------------------------------------------------");
DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(new AnswersDiffCallback(newAnswers, oldAnswers), true);
diffResult.dispatchUpdatesTo(new ListUpdateCallback() {
@Override
public void onInserted(int position, int count) {
try {
Log.d(TAG, String.format("onInserted: (position, count) = (%d, %d)", position, count));
for (int i = position; i < position + count; i++) {
Log.d(TAG, "onInserted: newAnswer.text = " + newAnswers.get(i).getText());
}
} catch (Exception ex) {
Log.e(TAG, "onInserted: Exception", ex);
}
Log.d(TAG, "-----------------------------------------------------------------------------");
}
@Override
public void onRemoved(int position, int count) {
try {
Log.d(TAG, "onRemoved: (position, count) = (" + position + ", " + count + ")");
for (int i = position; i < position + count; i++) {
Log.d(TAG, String.format("onRemoved: (oldAnswer.id, oldAnswer.text) = (%s, %s)", oldAnswers.get(i).getId(), oldAnswers.get(i).getText()));
}
} catch (Exception ex) {
Log.e(TAG, "onRemoved: Exception", ex);
}
Log.d(TAG, "-----------------------------------------------------------------------------");
}
@Override
public void onMoved(int fromPosition, int toPosition) {
try {
Log.d(TAG, "onMoved: (fromPosition, toPosition) = (" + fromPosition + ", " + toPosition + ")");
Log.d(TAG, String.format("onMoved: (oldAnswer.id, oldAnswer.text) = (%s, %s)", oldAnswers.get(fromPosition).getId(), oldAnswers.get(fromPosition).getText()));
Log.d(TAG, String.format("onMoved: (newAnswer.id, newAnswer.text) = (%s, %s)", newAnswers.get(toPosition).getId(), newAnswers.get(toPosition).getText()));
} catch (Exception ex) {
Log.e(TAG, "onMoved: Exception", ex);
}
Log.d(TAG, "-----------------------------------------------------------------------------");
}
@Override
public void onChanged(int position, int count, @Nullable Object payload) {
try {
Log.d(TAG, "onChanged: (position, count) = (" + position + ", " + count + ")");
for (int i = position; i < position + count; i++) {
Log.d(TAG, String.format("onChanged: (oldAnswer.id, oldAnswer.text) = (%s, %s)", oldAnswers.get(i).getId(), oldAnswers.get(i).getText()));
Log.d(TAG, String.format("onChanged: (newAnswer.id, newAnswer.text) = (%s, %s)", newAnswers.get(i).getId(), newAnswers.get(i).getText()));
}
} catch (Exception ex) {
Log.e(TAG, "onChanged: Exception", ex);
}
Log.d(TAG, "-----------------------------------------------------------------------------");
}
});
这是除了我有异常(exception)的logcat:
2019-06-19 16:32:00.461 24515-24515/com.example.myApp D/AdminQuestionsFragment: answers: oldAnswers = [{"count":0,"id":"5d09a1236969e249cca42e96","questionId":"5d09a1236969e249cca42e95","text":"old answer 0"},{"count":0,"id":"5d09a1236969e249cca42e97","questionId":"5d09a1236969e249cca42e95","text":"old answer 1"}]
2019-06-19 16:32:00.501 24515-24515/com.example.myApp D/AdminQuestionsFragment: answers: newAnswers = [{"count":0,"id":"5d09a1236969e249cca42e97","questionId":"5d09a1236969e249cca42e95","text":"old answer 1"},{"text":"new answer 0"},{"text":"new answer 1"},{"text":"new answer 2"}]
2019-06-19 16:32:00.501 24515-24515/com.example.myApp D/AdminQuestionsFragment: -----------------------------------------------------------------------------
2019-06-19 16:35:19.550 24515-24515/com.example.myApp D/AdminQuestionsFragment: onInserted: (position, count) = (2, 3)
2019-06-19 16:35:19.550 24515-24515/com.example.myApp D/AdminQuestionsFragment: onInserted: newAnswer.text = new answer 1
2019-06-19 16:35:19.550 24515-24515/com.example.myApp D/AdminQuestionsFragment: onInserted: newAnswer.text = new answer 2
2019-06-19 16:35:19.599 24515-24515/com.example.myApp E/AdminQuestionsFragment: onInserted: Exception
java.lang.IndexOutOfBoundsException: Index: 4, Size: 4
at java.util.ArrayList.get(ArrayList.java:437)
at com.example.myApp.views.AdminQuestionsFragment$5.onInserted(AdminQuestionsFragment.java:333)
at androidx.recyclerview.widget.BatchingListUpdateCallback.dispatchLastEvent(BatchingListUpdateCallback.java:61)
at androidx.recyclerview.widget.BatchingListUpdateCallback.onRemoved(BatchingListUpdateCallback.java:96)
at androidx.recyclerview.widget.DiffUtil$DiffResult.dispatchRemovals(DiffUtil.java:921)
at androidx.recyclerview.widget.DiffUtil$DiffResult.dispatchUpdatesTo(DiffUtil.java:836)
at com.example.myApp.views.AdminQuestionsFragment.lambda$onActivityResult$8$AdminQuestionsFragment(AdminQuestionsFragment.java:320)
at com.example.myApp.views.-$$Lambda$AdminQuestionsFragment$KZmQo8gdnjCYX1JsaACEVkjSd1s.onChanged(Unknown Source:8)
at androidx.lifecycle.LiveData.considerNotify(LiveData.java:113)
at androidx.lifecycle.LiveData.dispatchingValue(LiveData.java:126)
at androidx.lifecycle.LiveData$ObserverWrapper.activeStateChanged(LiveData.java:424)
at androidx.lifecycle.LiveData$LifecycleBoundObserver.onStateChanged(LiveData.java:376)
at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:361)
at androidx.lifecycle.LifecycleRegistry.addObserver(LifecycleRegistry.java:188)
at androidx.lifecycle.LiveData.observe(LiveData.java:185)
at com.example.myApp.views.AdminQuestionsFragment.onActivityResult(AdminQuestionsFragment.java:387)
at androidx.fragment.app.FragmentActivity.onActivityResult(FragmentActivity.java:170)
at android.app.Activity.dispatchActivityResult(Activity.java:7454)
at android.app.ActivityThread.deliverResults(ActivityThread.java:4353)
at android.app.ActivityThread.handleSendResult(ActivityThread.java:4402)
at android.app.servertransaction.ActivityResultItem.execute(ActivityResultItem.java:49)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
2019-06-19 16:35:19.599 24515-24515/com.example.myApp D/AdminQuestionsFragment: -----------------------------------------------------------------------------
2019-06-19 16:35:19.600 24515-24515/com.example.myApp D/AdminQuestionsFragment: onRemoved: (position, count) = (0, 1)
2019-06-19 16:35:19.603 24515-24515/com.example.myApp D/AdminQuestionsFragment: onRemoved: (oldAnswer.id, oldAnswer.text) = (5d09a1236969e249cca42e96, old answer 0)
2019-06-19 16:35:19.603 24515-24515/com.example.myApp D/AdminQuestionsFragment: -----------------------------------------------------------------------------
问题出在这条线上:
2019-06-19 16:35:19.550 24515-24515/com.example.myApp D/AdminQuestionsFragment: onInserted: (position, count) = (2, 3)
为什么仓位不是1？
更新1
如果我有2个项目的旧列表，并且我在索引1处删除了该项目，然后将3个项目添加到列表的末尾，则这是logcat:
2019-06-19 18:25:24.368 28118-28118/com.example.myApp D/AdminQuestionsFragment: answers: oldAnswers = [{"count":0,"id":"5d09a1236969e249cca42e96","questionId":"5d09a1236969e249cca42e95","text":"old answer 0"},{"count":0,"id":"5d09a1236969e249cca42e97","questionId":"5d09a1236969e249cca42e95","text":"old answer 1"}]
2019-06-19 18:25:24.370 28118-28118/com.example.myApp D/AdminQuestionsFragment: answers: newAnswers = [{"count":0,"id":"5d09a1236969e249cca42e96","questionId":"5d09a1236969e249cca42e95","text":"old answer 0"},{"text":"new answer 0"},{"text":"new answer 1"},{"text":"new answer 2"}]
2019-06-19 18:25:24.370 28118-28118/com.example.myApp D/AdminQuestionsFragment: -----------------------------------------------------------------------------
2019-06-19 18:25:24.370 28118-28118/com.example.myApp D/AdminQuestionsFragment: onRemoved: (position, count) = (1, 1)
2019-06-19 18:25:24.371 28118-28118/com.example.myApp D/AdminQuestionsFragment: onRemoved: (oldAnswer.id, oldAnswer.text) = (5d09a1236969e249cca42e97, old answer 1)
2019-06-19 18:25:24.371 28118-28118/com.example.myApp D/AdminQuestionsFragment: -----------------------------------------------------------------------------
2019-06-19 18:25:24.372 28118-28118/com.example.myApp D/AdminQuestionsFragment: onInserted: (position, count) = (1, 3)
2019-06-19 18:25:24.372 28118-28118/com.example.myApp D/AdminQuestionsFragment: onInserted: newAnswer.text = new answer 0
2019-06-19 18:25:24.372 28118-28118/com.example.myApp D/AdminQuestionsFragment: onInserted: newAnswer.text = new answer 1
2019-06-19 18:25:24.372 28118-28118/com.example.myApp D/AdminQuestionsFragment: onInserted: newAnswer.text = new answer 2
2019-06-19 18:25:24.372 28118-28118/com.example.myApp D/AdminQuestionsFragment: -----------------------------------------------------------------------------
最佳答案
for (int i = position; i < position + count; i++) {
Log.d(TAG, "onInserted: newAnswer.text = " + newAnswers.get(i).getText());
}
这个循环肯定会抛出
IndexOutOfBoundError。 count是已添加的项目数。 position是新项目的位置。当您执行position + count时，在某些时候绝对会超过列表的大小。因此，错误。在删除之后和添加新项目之前，您是否调用
dispatchUpdates？我认为首先是要计算要插入的项目，然后是要删除的项目，因此
onInserted中的位置为2。如果要批量更新，可以将
ListUpdateCallback包装在BatchingListUpdateCallback中。关于java - 使用DiffUtil将更新分派(dispatch)到ListUpdateCallback时如何解决错误的位置，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/56670162/