我已经使用了数据绑定一段时间了,即使现在它也不适用于JDK 8和API 24.我仍然找到一种以更简单的方式使用数据绑定的方法.但是,当我使用以下方式进行精确的双向数据绑定时(在我看来,双向数据绑定就像这里(
What is two way binding?),有些奇怪的事情发生了.
1.双向数据绑定(以xml为单位)
android:text="@={testStr}"
这在官方文档中没有提到(https://developer.android.com/topic/libraries/data-binding/index.html,这个页面通常会更新,现在可能会更改).但它可以将变量绑定到xml.
2. ObservableField属性
这里的例子(https://developer.android.com/topic/libraries/data-binding/index.html#observablefields)
private static class User {
public final ObservableField<String> firstName =
new ObservableField<>();
public final ObservableField<String> lastName =
new ObservableField<>();
public final ObservableInt age = new ObservableInt();
}
3.将模型类扩展为BaSEObservable
private static class User extends BaSEObservable { private String firstName; private String lastName; @Bindable public String getFirstName() { return this.firstName; } @Bindable public String getLastName() { return this.lastName; } public void setFirstName(String firstName) { this.firstName = firstName; notifyPropertyChanged(BR.firstName); } public void setLastName(String lastName) { this.lastName = lastName; notifyPropertyChanged(BR.lastName); } }
模型类必须扩展到BaSEObservable类,并且getter方法必须使用“@Bindable”进行注释,并且setter方法需要使用绑定xml中的相应命名调用方法notifyPropertyChange().
我的问题是,我想知道三种绑定方法的缺点和优点.当然,我知道第一个会更容易.但是我在文档和某些网站上找到了一些时刻.它在下一刻消失了.官方文档未经任何明确公告而更改.我仍然想知道我应该使用第一种方法,所以我必须准备改变方法2或3.
Student_XML2WAY.java
public class Student_XML2WAY {
private int age;
private String name;
public int getAge() {
return age;
}
public void setAge(int pAge) {
age = pAge;
}
public String getName() {
return name;
}
public void setName(String pName) {
name = pName;
}
}
Student_ObserField.java
public class Student_ObserField {
private ObservableInt age;
private ObservableField<String> name;
public Student_ObserField() {
age = new ObservableInt();
name = new ObservableField<>();
}
public ObservableInt getAge() {
return age;
}
public ObservableField<String> getName() {
return name;
}
}
Student_Extend.java
public class Student_Extend extends BaSEObservable{ private int age; private String name; @Bindable public int getAge() { return age; } public void setAge(int pAge) { age = pAge; notifyPropertyChanged(BR.student3); } @Bindable public String getName() { return name; } public void setName(String pName) { name = pName; notifyPropertyChanged(BR.student3); } }
activity_main.xml中
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="student1"
type="example.com.testerapplication.sp.bean.Student_XML2WAY"/>
<variable
name="student2"
type="example.com.testerapplication.sp.bean.Student_ObserField"/>
<variable
name="student3"
type="example.com.testerapplication.sp.bean.Student_Extend"/>
</data>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@={student1.name}"/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@{student2.name}"/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@{student3.name}"/>
<Button
android:id="@+id/btn1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="update"/>
</LinearLayout>
</layout>
活动类
public class MainActivity extends AppCompatActivity {
private Student_XML2WAY mStudent1;
private Student_ObserField mStudent2;
private Student_Extend mStudent3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ActivityMainBinding binding = DataBindingUtil.inflate(LayoutInflater.from(this),R.layout.activity_main,null,false);
mStudent1 = new Student_XML2WAY();
mStudent1.setName("XML First");
mStudent2 = new Student_ObserField();
mStudent2.getName().set("ObserField Second");
mStudent3 = new Student_Extend();
mStudent3.setName("Extend Third");
binding.setStudent1(mStudent1);
binding.setStudent2(mStudent2);
binding.setStudent3(mStudent3);
setContentView(binding.getRoot());
binding.btn1.setonClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mStudent1.setName("Student1");
mStudent2.getName().set("Student2");
mStudent3.setName("Student3");
}
});
}
}
解决方法
您的Student_XML2WAY.java不适用于双向绑定,因为它不满足这样做的要求(BaSEObservable,Bindable或类似的东西).
如果我将直接访问模型,我将使用BaSEObservable,就像在Student_Extend中一样.我将在我的Activity中有一个Student_Extend实例,我将在onCreate中设置变量：
Student mStudent = new Student("John Doe",42); //
binding.setStudent(mStudent);
//later:
mStudent.setAge(37);
如果正确实施,这也将改变UI(以及模型中)的年龄.
如果您不想直接访问模型并希望使用viewmodel,我可以使用ObervableFields：
public class Student {
private String name;
private int age;
//Corresponding setters and getters
}
public class Studentviewmodel {
private ObservableField<Student> mStudentField = new ObservableField<>();
//if I have a large model class,and only want to use some fields,//I create some getters (and setters,for the two way attributes)
//Something like this:
public int getAge() {
return mStudentField.get().getAge();
}
public void setAge(int newAge) {
return mStudentField.get().setAge(newAge);
}
}
因此,我在Activity中创建了一个Studentviewmodel实例,并将其设置为绑定.伪xml看起来像这样：
<layout>
<data>
<variable name="studentviewmodel"
type="locaction.of.Studentviewmodel"> <!-- or do an import -->
</data>
<EditText
android:text="@={studentviewmodel.age}"/>
</layout>
因此,viewmodel方法更“清晰”,因为您几乎将所有与视图有关的内容外包.把你的BindingAdapter,点击方法,转换器方法放在那里,保持你的活动干净.此外,您不直接更改您的模型.
对于简单的类和项目,这种方法可能过度.
