如何像 React.js 一样在 Java 中进行实时值更改

Question

I got used to React.js for 6 months and starting to develop an app from Java scratch for my Android application.

In React.js , All it does when the boolean changed from false to true:

this.state = {
    checkmarkChecked: false
}
if (this.state.checkmarkChecked) {
    //If the checkmarkChecked is true
    //TODO: show all checks
} else {
    //If the checkmarkChecked is false
    //TODO: hide all checks
}

If the checkmarkChecked was switched to true, it calls the true one to show.

Now I am new to Java for Android development, i tried one of these:

//onCreate
while (true) {
    if (checkmarkChecked) {
        System.out.println("True");
    } else {
        System.out.println("False");
    }
}

Actually, the while(true) causes my app to freeze at the start.

Answer 1

You may use a MutableLiveData that wraps a Boolean , and register the activity to observe it with .observe() .

Whenever this boolean value changes, then onChanged() callback will be triggered with the new value of the boolean.

public class MainActivity extends AppCompatActivity {

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

        final MutableLiveData<Boolean> state = new MutableLiveData<>(false);
    
        state.observe(this, new Observer<Boolean>() {
            @Override
            public void onChanged(Boolean newValue) {
                if (newValue) {
                    Toast.makeText(MainActivity.this, "True", Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(MainActivity.this, "False", Toast.LENGTH_SHORT).show();
                }
            }
        });
        
        Button myButton = findViewById(..);
        
        myButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                state.setValue(!state.getValue());
            }
        });
        
    }
}

The button just for toggling the boolean value to test it