我需要了解数据绑定库如何确定其BindingAdapter的执行顺序.如果我有一个View的两个BindingAdapter,如果View有两个属性对应于那些BindingAdapters,它将如何确定首先执行哪个适配器？我问,因为执行顺序在我的情况下很重要.
我有以下BindingAdapter / s：
public class SpinnerBindingAdapter {
@BindingAdapter(value = {"entries"})
public static void setEntries(Spinner spinner,List<? extends SpinnerItem> spinnerItems) {
for (int i = 0; i < spinnerItems.size(); i++) {
spinnerItems.get(i).setIndex(i);
}
ArrayAdapter<? extends SpinnerItem> adapter =
new ArrayAdapter<>(spinner.getContext(),R.layout.spinner_item,spinnerItems);
spinner.setAdapter(adapter);
}
@InverseBindingAdapter(attribute = "selectedItem",event = "selectedItemAttrChanged")
public static Object getSelectedItem(Spinner spinner) {
Object selectedItem = spinner.getSelectedItem();
return selectedItem;
}
@BindingAdapter(value = {"selectedItem"})
public static void setSelectedItem(Spinner spinner,SpinnerItem spinnerItem) {
if (spinner.getAdapter() == null) {
return;
}
// Other code omitted for simplicity
}
@BindingAdapter(value = {"selectedItemAttrChanged"},requireAll = false)
public static void setOnItemSelectedListener(Spinner spinner,final InverseBindingListener selectedItemChange) {
if (selectedItemChange == null) {
spinner.setOnItemSelectedListener(null);
} else {
spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parent,View view,int position,long id) {
selectedItemChange.onChange();
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
});
}
}
}
这是我如何填充Spinner并设置选择：
<Spinner
android:id="@+id/spinner_system_activity_edit_tracker_unit"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="fill_horizontal"
app:entries="@{DatabaseModel.queryForAll()}"
app:selectedItem="@={object.selectedItem}"/>
DatabaseModel.queryForAll是一个静态方法,它查询数据库并返回一个对象列表,然后将其提供给BindingAdapter. BindingAdapter获取此列表,使用索引更新其每个项目,并将其设置为微调器的适配器.
无论出于何种原因,始终首先调用“setSelectedItem”BindingAdapter.这是不可取的,因为我需要首先初始化条目.如果先未初始化,则首次调用setSelectedItem时,spinner.getAdapter()将为null.这意味着以前保存的选择将无法恢复.
解决方法
Android数据绑定中无法保证执行顺序.因此,您应该合并依赖于多个属性的绑定适配器.在您的情况下,您需要合并selectedItem和条目的绑定适配器.
@BindingAdapter(value = {"selectedItem","entries"},requireAll = false)
public static void setSelectedItem(Spinner spinner,SpinnerItem spinnerItem,List<? extends SpinnerItem> spinnerItems) {
// Set entries attribute when provided
if (spinnerItems != null) {
for (int i = 0; i < spinnerItems.size(); i++) {
spinnerItems.get(i).setIndex(i);
}
ArrayAdapter<? extends SpinnerItem> adapter =
new ArrayAdapter<>(spinner.getContext(),spinnerItems);
spinner.setAdapter(adapter);
}
// set selectedItem attribute when provided
if (spinnerItem != null) {
if (spinner.getAdapter() == null) {
return;
}
// Other code omitted for simplicity
}
}
