Android面试题之Kotlin Jetpack DataBinding

AntDream

发布于 2024-06-13 21:00:05

730

发布于 2024-06-13 21:00:05

文章被收录于专栏：程序员修炼之路

作用

让布局文件承担了部分原本属于页面的工作，使页面与布局耦合度进一步降低

应用

需要在build.gradle中开启DataBinding

defaultConfig {
    minSdk 21
    targetSdk 31
    versionCode 1
    versionName "1.0"

    testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    consumerProguardFiles "consumer-rules.pro"

    //开启
    dataBinding{
        enabled = true
    }
}

activity中设置

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ActivityMainBinding activityMainBinding = DataBindingUtil.setContentView(this,R.layout.activity_main);
        activityMainBinding.setIdol(new Idol("我"));

    }
}

然后布局里面改为databinding布局

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>
        <variable
            //变量名字
            name="idol"
            type="com.example.databinding.Idol" />
    </data>
    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            tools:text="TextView"
            //获取变量属性
            android:text="@{idol.name}"
            android:textSize="24sp"
            app:layout_constraintBottom_toTopOf="@+id/guideline2"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.5" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

import

布局里还可以import类

 public class IdolUtils {
        public static String getIdolName() {
            return "name is name";
        }
    }



    //布局文件中
     <data>

        <variable
            name="idol"
            type="com.example.databinding.Idol" />
        <import type="com.example.databinding.IdolUtils"/>
    </data>

    //使用
    android:text="@{IdolUtils.getIdolName()}"

事件绑定

定义事件处理类

public class EventHandleListener {
    private Context context;

    public EventHandleListener(Context context) {
        this.context = context;
    }

    public void onClick(View view){
        Toast.makeText(context, "哈哈哈",Toast.LENGTH_SHORT).show();
    }
}

布局中绑定事件处理

<data>

    <variable
        name="idol"
        type="com.example.databinding.Idol" />
    <variable
        name="eventHandle"
        type="com.example.databinding.EventHandleListener" />
    <import type="com.example.databinding.IdolUtils"/>
</data>

<Button
    android:id="@+id/button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Button"
    android:onClick="@{eventHandle.onClick}"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="@+id/guideline2" />

activity中设置

activityMainBinding.setEventHandle(new EventHandleListener(this));

二级页面的绑定

二级页面中也要是binding
然后用app命名空间传给二级页面

  //主页面
    <include layout="@layout/sub"
            app:idol="@{idol}"/>

    //子页面
    <layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools">
        <data>
            <variable
                name="idol"
                type="com.example.databinding.Idol" />
        </data>
        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">
            <TextView
                android:id="@+id/textView"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@{idol.name}"
                android:textSize="24sp"
                app:layout_constraintBottom_toTopOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                tools:text="TextView" />
        </androidx.constraintlayout.widget.ConstraintLayout>
    </layout>

用BaseObservable双向绑定

需要继承BaseObservable

public class UserViewModel extends BaseObservable {
    private User user;

    public UserViewModel() {
        this.user = new User("name");
    }

    @Bindable
    public String getUserName() {
        return user.getName();
    }

    public void setUserName(String userName){
        if (userName != null && userName.equals(user.name)){
            user.name = userName;
            notifyPropertyChanged(BR.userName);
        }
    }
}

布局里使用也有点变化

//导入数据这里没有变
<data>
    <variable
        name="userViewModel"
        type="com.example.databinding2.UserViewModel" />

</data>

<EditText
    android:id="@+id/editTextTextPersonName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:ems="10"
    android:inputType="textPersonName"
    //主要是这里变化，多了一个=号
    android:text="@={userViewModel.userName}"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

activity里设置

 ActivityMainBinding viewDataBinding = DataBindingUtil.setContentView(this, R.layout.activity_main);
    viewDataBinding.setUserViewModel(new UserViewModel());

用ObservableField进行双向绑定，这个更加简洁

主要是ViewModel里要修改下

public class UserViewModel2 {
    private ObservableField<User> observableField;
    private User user;

    public UserViewModel2() {
        this.user = new User("name");
        observableField = new ObservableField<>();
        observableField.set(user);
    }

    public String getUserName() {
        return observableField.get().name;
    }

    public void setUserName(String userName){
        if (userName != null && userName.equals(user.name)){
            observableField.get().setName(userName);
        }
    }
}

布局和activity里都一样