如何在Android MVVM架构中实现对话框选择选项

Posted 2021-04-04

我正试图进入MVVM模式，我的问题是我不确定我是否正确使用它。 View负责所有UI操作（比如show stuff？）但是当我们需要在逻辑中改变某些东西时会发生什么。

所以我真正想做的是，显示一个包含某些选项的对话框，选择一个并重新加载应用程序。

我已经实现了MainActivity类中的函数，并且在需要操作时使用mCountrySelection.show（）。

    public void createCountriesDialog()
    {
        AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(MainActivity.this);
        dialogBuilder.setTitle("Available Countries");

        GridView gridView = new GridView(MainActivity.this);
        final String[] countries = getResources().getStringArray(R.array.countries);
        final String[] codes = getResources().getStringArray(R.array.codes);
        ArrayAdapter<String> arrayAdapter = new ArrayAdapter<>(getApplicationContext(), android.R.layout.simple_list_item_1, countries);
        gridView.setAdapter(arrayAdapter);

        dialogBuilder.setView(gridView);
        dialogBuilder.setNegativeButton("Close", new DialogInterface.OnClickListener()
        {
            @Override
            public void onClick(DialogInterface dialog, int which)
            {
                dialog.dismiss();
            }
        });

        mCountrySelection = dialogBuilder.create();

        gridView.setOnItemClickListener(new AdapterView.OnItemClickListener()
        {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id)
            {
                PreferencesManager.setCountry(countries[position], codes[position]);
                getSupportActionBar().setTitle(PreferencesManager.getCountry());

                FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
                fragmentTransaction.replace(R.id.a_main_frame, new ArticlesFragment(), "ArticlesFragment");
                fragmentTransaction.commit();

                mCountrySelection.dismiss();
            }
        });
    }

    public void createAboutDialog()
    {
        AlertDialog.Builder aboutBuilder = new AlertDialog.Builder(MainActivity.this);
        aboutBuilder.setTitle("Top News v1.0");
        aboutBuilder.setMessage("Simple application for displaying Top Headlines from newsapi.org.

Icons made by Freepik from www.flaticon.com.");
        aboutBuilder.setNegativeButton("Close", new DialogInterface.OnClickListener()
        {
            public void onClick(DialogInterface dialog, int id)
            {
                dialog.dismiss();
            }
        });

        mAbout = aboutBuilder.create();
    }

答案

创建1个接口ItemClick并从您调用Dialog的位置实现此接口。

public interface ItemClick{
public void onClick(int position, String country);
}

将此接口引用传递给对话框方法

public void createCountriesDialog(ItemClick listner)
    {
        AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(MainActivity.this);
        dialogBuilder.setTitle("Available Countries");

        GridView gridView = new GridView(MainActivity.this);
        final String[] countries = getResources().getStringArray(R.array.countries);
        final String[] codes = getResources().getStringArray(R.array.codes);
        ArrayAdapter<String> arrayAdapter = new ArrayAdapter<>(getApplicationContext(), android.R.layout.simple_list_item_1, countries);
        gridView.setAdapter(arrayAdapter);

        dialogBuilder.setView(gridView);
        dialogBuilder.setNegativeButton("Close", new DialogInterface.OnClickListener()
        {
            @Override
            public void onClick(DialogInterface dialog, int which)
            {
                dialog.dismiss();
                listener = null;
            }
        });

        mCountrySelection = dialogBuilder.create();

        gridView.setOnItemClickListener(new AdapterView.OnItemClickListener()
        {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id)
            { 
                listener.onclick(position, countries[position]);
                PreferencesManager.setCountry(countries[position], codes[position]);
                getSupportActionBar().setTitle(PreferencesManager.getCountry());

                FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
                fragmentTransaction.replace(R.id.a_main_frame, new ArticlesFragment(), "ArticlesFragment");
                fragmentTransaction.commit();

                mCountrySelection.dismiss();
            }
        });
    }

然后，当您单击网格项时，使用接口引用调用onclick方法现在，当您将在onClick（int pos，String country）中收到回调时

使用您的视图模型进行api调用和重新加载屏幕。

在对话框关闭时设置listener = null以避免内存泄漏

另一答案

1-在你的LiveData中暴露一个可变的Observer或ViewModel

public MutableLiveData<Pair<String, String>> countryInfo = new MutableLiveData<>()

2-将用户选择传递给ViewModel

@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id)
{
   viewModel.countryInfo.setValue(new Pair(countries[position], codes[position]))
   mCountrySelection.dismiss();
}

3-在ViewModel中运行用例（业务逻辑）（将信息上传到服务器，将其保存在数据库中等）

4-通过暴露另一个View更新Observable（在这种情况下相同的countryInfo将起作用）在MainActivity中观察countryInfo：

viewmodel.countryInfo.observe(this, new Observer<String>() {
   @Override
   public void onChanged(@Nullable final String newName) {
      // Update the UI
      PreferencesManager.setCountry(countries[position], codes[position]);
      getSupportActionBar().setTitle(PreferencesManager.getCountry());

      getSupportFragmentManager().beginTransaction();
         .replace(R.id.a_main_frame, new ArticlesFragment(), "ArticlesFragment");
         .commit();
   }
});

P.S：最好将此行移至ViewModel，因为它包含业务逻辑的一部分：

PreferencesManager.setCountry(countries[position], codes[position]);