Jetpack架构组件_ViewModel组件

Jetpack架构组件_ViewModel组件_2.AndroidViewModel

news2025/1/11 6:55:56

1.AndroidViewModel简介

“Application context aware ViewModel.

Subclasses must have a constructor which accepts Application as the only parameter.”

AndroidViewModel是感知应用程序上下文的ViewModel。子类必须有一个接受Application作为唯一参数的构造函数。

2.示例代码

2.1创建项目

创建AndroidViewModelSample项目。

2.2 创建MyAndroidViewModel

创建MyAndroidViewModel。

package com.gaoting.androidviewmodelsample;

import android.app.Application;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;

public class MyAndroidViewModel extends AndroidViewModel {

    public MyAndroidViewModel(@NonNull Application application) {
        super(application);
        Toast.makeText(application,"hello,I'm AndroidViewModel.",Toast.LENGTH_SHORT).show();
    }
}

2.3创建ViewModelFactory

创建ViewModelFactory类。

package com.gaoting.androidviewmodelsample;

import android.app.Application;

import androidx.annotation.NonNull;
import androidx.lifecycle.ViewModel;
import androidx.lifecycle.ViewModelProvider;

public class ViewModelFactory implements ViewModelProvider.Factory {

    Application mAapp;

    public ViewModelFactory(Application app) {
        this.mAapp = app;
    }

    @NonNull
    @Override
    public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
        if(modelClass.isAssignableFrom(MyAndroidViewModel.class)){
            return (T) new MyAndroidViewModel(mAapp);
        }
        return null;
    }
}

2.4修改MainActivity

修改MainActivity类。关键方法：ViewModelFactory就是2.3创建的工厂类。

ViewModelProvider viewModelProvider = new ViewModelProvider(this,new ViewModelFactory(getApplication()));
myAndroidViewModel = viewModelProvider.get(MyAndroidViewModel.class);

package com.gaoting.androidviewmodelsample;

import android.os.Bundle;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;
import androidx.lifecycle.ViewModelProvider;

public class MainActivity extends AppCompatActivity {

    MyAndroidViewModel myAndroidViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ViewModelProvider viewModelProvider = new ViewModelProvider(this,new ViewModelFactory(getApplication()));
        myAndroidViewModel = viewModelProvider.get(MyAndroidViewModel.class);
    }
}