liveData和viewBinding的使用

ViewModel:
官方解释：保存UI数据的类，会在配置变更（如手机屏幕的旋转）后继续存在。
view Model不应持有context，否则在Activity销毁后View Model仍然持有Activity的context，造成内存泄漏；可以继承AndroidViewModel，或者选择application context

liveData:
1.建立data类

public class Time {
    private MutableLiveData<Integer> seconds = new MutableLiveData<>();

    public MutableLiveData<Integer> getSeconds() {
        return seconds;
    }
}
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2.继承View Model

public class TestViewModel extends ViewModel {
    private Time time;

    public TestViewModel(){
        time = new Time();
        // 修改liveData包装的数据，主线程用setValue，其他线程PostValue
        time.getSeconds().setValue(0);
    }

    public Time getLiveData(){
        return time;
    }
}
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3.observe数据

private TestViewModel vm;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    vm = new TestViewModel();
    vm.getLiveData().getSeconds().observe(this, new Observer<Integer>() {
        @Override
        public void onChanged(Integer integer) {
            EditText ed = findViewById(R.id.ed);
            ed.setText(""+integer);
        }
    });
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viewBinding:
1.build.gradle添加

buildFeatures {
    viewBinding true
}
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根视图和所有有ID的视图都会根据xml文件名称，生成对应的Binding类
2. 在Activity中使用view Binding

ActivityMainBinding binding = ActivityMainBinding.inflate(getLayoutInflater());
View view = binding.getRoot();
setContentView(view);
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如果找不到Binding类，可能是名字错了，顺序再调一下可能就对了
在Fragment中使用view Binding

 @Override
    public View onCreateView (LayoutInflater inflater,
                              ViewGroup container,
                              Bundle savedInstanceState) {
        ActivityMainBinding binding = ResultProfileBinding.inflate(inflater, container, false);
        View view = binding.getRoot();
        return view;
    }
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由于fragment的生命周期更长，所以务必在destroy解除绑定

@Override
    public void onDestroyView() {
        super.onDestroyView();
        binding = null;
    }
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