具有2向绑定的Android微调器设置选择 [英] Android Spinner Setting Selection with 2-Way Binding
问题描述
在配置2向数据绑定时,我正在努力获得与Android微调器一起使用的某些功能。我想通过 android:selectedItemPosition
上的2-way数据绑定设置微调器的初始值。微调器条目由ViewModel初始化并正确填充,因此数据绑定似乎正常工作。
问题在于2向绑定 selectedItemPosition
。该变量已由ViewModel初始化为5,但微调框的选定项目保持为0(第一个项目)。调试时,似乎ObservableInt的值最初为5(已设置),但在executeBindings的第二阶段重置为零。
test_spinner_activity.xml
< layout xmlns:tools = http://schemas.android.com/tools
xmlns:android = http://schemas.android.com/apk/res/android
xmlns:app = http:// schemas.android.com/apk/res-auto\">
< data>
<变量名称= viewModel
type = com.aapp.viewmodel.TestSpinnerViewModel />
< / data>
< LinearLayout android:layout_width = match_parent
android:layout_height = wrap_content>
< android.support.v7.widget.AppCompatSpinner
android:layout_width = wrap_content
android:layout_height = match_parent
android:id = @ + id / sTimeHourSpinner
android:selectedItemPosition = @ = {viewModel.startHourIdx}
android:entries = @ {viewModel.startTimeHourSelections} />
< / LinearLayout>
< / layout>
TestSpinnerViewModel.java
公共类TestSpinnerViewModel {
public final ObservableArrayList< String> startTimeHourSelections = new ObservableArrayList<>();
public final ObservableInt startHourIdx = new ObservableInt();
public TestSpinnerViewModel(Context context){
this.mContext = context;
for(int i = 0; i< 24; i ++){
int hour = i;
startTimeHourSelections.add(df.format(hour));
}
startHourIdx.set(5);
}
}
TestSpinnerActivity.java
公共类TestSpinnerActivity扩展了AppCompatActivity {
私人TestSpinnerActivityBinding绑定;
private TestSpinnerViewModel mTestSpinnerViewModel;
@Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
绑定= DataBindingUtil.bind(findViewById(R.id.test_spinner));
mTestSpinnerViewModel = new TestSpinnerViewModel(this);
binding.setViewModel(mTestSpinnerViewModel);
}
我正在使用Android Studio 2.2.2,并且启用了数据绑定。
感谢您的建议。但是我找到了自己问题的答案。事实证明,将 android:selectedItemPosition = @ = {viewModel.startHourIdx}
变量从初始值5重置为0的原因是由于声明顺序 selectedItemPosition
和 entries
属性的值。在我的示例中,它们以特定顺序声明,并且自动生成的绑定代码以相同顺序进行初始化。
因此,即使 selectedItemPosition
正确设置了条目的初始化, code>导致ArrayAdapter的实例化,该适配器将
selectedItemPosition
重置为0。
因此,此修复程序是交换布局文件中的两个属性声明。
< data>
<变量名称= viewModel
type = com.aapp.viewmodel.TestSpinnerViewModel />
< / data>
< LinearLayout android:layout_width = match_parent
android:layout_height = wrap_content>
< android.support.v7.widget.AppCompatSpinner
android:layout_width = wrap_content
android:layout_height = match_parent
android:id = @ + id / sTimeHourSpinner
android:entries = @ {viewModel.startTimeHourSelections}
android:selectedItemPosition = @ = {viewModel.startHourIdx} />
< / LinearLayout>
I am struggling to get some functionality to work with Android spinners when configured with 2-way databinding. I would like to set the initial value of the spinner via the 2-way databinding on android:selectedItemPosition
. The spinner entries are initialised by the ViewModel and are populated correctly, hence databinding appears to be working correctly.
The problem is with the 2-way binding of selectedItemPosition
. The variable is initialised to 5 by the ViewModel but the spinner's selected item remains at 0 (the first item). When debugging it appears that the value of the ObservableInt is initially 5 (as set) but is reset to zero during the second phase of executeBindings.
Any help would be appreciated.
test_spinner_activity.xml
<layout xmlns:tools="http://schemas.android.com/tools"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<data>
<variable name="viewModel"
type="com.aapp.viewmodel.TestSpinnerViewModel"/>
</data>
<LinearLayout android:layout_width="match_parent"
android:layout_height="wrap_content">
<android.support.v7.widget.AppCompatSpinner
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:id="@+id/sTimeHourSpinner"
android:selectedItemPosition="@={viewModel.startHourIdx}"
android:entries="@{viewModel.startTimeHourSelections}"/>
</LinearLayout>
</layout>
TestSpinnerViewModel.java
public class TestSpinnerViewModel {
public final ObservableArrayList<String> startTimeHourSelections = new ObservableArrayList<>();
public final ObservableInt startHourIdx = new ObservableInt();
public TestSpinnerViewModel(Context context) {
this.mContext = context;
for (int i=0; i < 24; i++) {
int hour = i;
startTimeHourSelections.add(df.format(hour));
}
startHourIdx.set(5);
}
}
TestSpinnerActivity.java
public class TestSpinnerActivity extends AppCompatActivity {
private TestSpinnerActivityBinding binding;
private TestSpinnerViewModel mTestSpinnerViewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
binding = DataBindingUtil.bind(findViewById(R.id.test_spinner));
mTestSpinnerViewModel = new TestSpinnerViewModel(this);
binding.setViewModel(mTestSpinnerViewModel);
}
I am using Android Studio 2.2.2 and Databinding is enabled.
thank you for your suggestions. But I found the answer to my own question. It turns out that the reason that the android:selectedItemPosition=@={viewModel.startHourIdx}
variable was being reset from the initialised value of 5 to 0 is because of the declaration order of the selectedItemPosition
and entries
attributes. In my example they were declared in that specific order and the auto-generated binding code produces initialisation in that same order.
Hence, even though the selectedItemPosition
was set correctly the initialisation of the entries
causes instantiation of the an ArrayAdapter which resets the selectedItemPosition
to 0.
Hence, the fix is to swap the two attribute declarations in the layout file.
<data>
<variable name="viewModel"
type="com.aapp.viewmodel.TestSpinnerViewModel"/>
</data>
<LinearLayout android:layout_width="match_parent"
android:layout_height="wrap_content">
<android.support.v7.widget.AppCompatSpinner
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:id="@+id/sTimeHourSpinner"
android:entries="@{viewModel.startTimeHourSelections}"
android:selectedItemPosition="@={viewModel.startHourIdx}"/>
</LinearLayout>
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