我有一个笔记记录活动,我希望能够编辑和保存(基本上覆盖)相同的笔记。
一旦我点击编辑MenuItem,我希望它隐藏,然后显示保存MenuItem。
我可以让编辑MenuItem不可见,但我无法显示保存MenuItem。我一直得到一个空指针异常。
这是我的edit_question_menu.xml
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<item
android:id="@+id/edit_question"
android:icon="@drawable/ic_edit_black_24dp"
android:title="Edit"
app:showAsAction="ifRoom"
android:visible="true">
</item>
<item
android:id="@+id/save_question"
android:icon="@drawable/ic_save_black_24dp"
android:title="Edit"
app:showAsAction="ifRoom"
android:visible="false">
</item>
</menu>
activity.java文件
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater menuInflater = getMenuInflater();
menuInflater.inflate(R.menu.edit_question_menu, menu);
MenuItem itemSave = menu.findItem(R.id.save_question);
itemSave.setVisible(false);
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.save_question:
saveQuestion();
return true;
case R.id.edit_question:
item.setVisible(false);
// MenuItem save_Question_MenuItem = findViewById(R.id.save_question);
// save_Question_MenuItem.setVisible(true);
enableEditMode();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
private void enableEditMode(){
MenuItem saveButton = findViewById(R.id.save_question);
getSupportActionBar().setHomeAsUpIndicator(R.drawable.ic_close_black_24dp);
questionEditText = findViewById(R.id.questionEditTextID);
mPostAnswerButton.setEnabled(false);
mPostAnswerButton.setBackgroundColor(getResources().getColor(android.R.color.darker_gray));
mCommentButton.setEnabled(false);
mCommentButton.setBackgroundColor(getResources().getColor(android.R.color.darker_gray));
saveButton.setVisible(true); **ERROR HAPPENS HERE**
}
任何和所有的帮助表示赞赏。这似乎相当简单,但我找不到一种方法让它工作。
save
MenuItem
应该在哪里可见:private boolean mShowSaveIcon
onPrepareOptionsMenu
(更新):@Override
public boolean onPrepareOptionsMenu(Menu menu) {
MenuItem item = menu.findItem(R.id.save_question);
item.setVisible(mShowSaveIcon);
menu.findItem(R.id.edit_question).setVisible(!mShowSaveIcon); // you can use negation of the same flag if one and only one of two menu items is visible; or create more complex logic
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.save_question:
mShowSaveIcon = false;
break;
case R.id.edit_question:
item.setVisible(false);
enableEditMode();
mShowSaveIcon = true;
break;
}
invalidateOptionsMenu();
return true;
}
private void enableEditMode(){
/// MenuItem saveButton = findViewById(R.id.save_question); // <--- NO THIS LINE
getSupportActionBar().setHomeAsUpIndicator(R.drawable.ic_close_black_24dp);
questionEditText = findViewById(R.id.questionEditTextID);
mPostAnswerButton.setEnabled(false);
mPostAnswerButton.setBackgroundColor(getResources().getColor(android.R.color.darker_gray));
mCommentButton.setEnabled(false);
mCommentButton.setBackgroundColor(getResources().getColor(android.R.color.darker_gray));
/// saveButton.setVisible(true); **ERROR HAPPENS HERE** // <--- NO THIS LINE
}