Question

如何将类属性应用于纯CSS中具有选择器的类？例如：

.one{color:red;}

.two{color:blue;}
.two:hover{ /*Apply class ".one" to class ".two" when the event is triggered */}

Answer 1

很简单：

.one {
    color: blue;
}
.two {
    color: red;
    &:hover {
        @extend .one;
    }
}

希望这有帮助！如果您曾经移植到SASS，您可以做一点清洁，如：

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    ActionBar actionBar = getSupportActionBar();

    if (actionBar != null){
        actionBar.setDisplayHomeAsUpEnabled(true);
        actionBar.setHomeButtonEnabled(true);
    }

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    final ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

    getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
        @Override
        public void onBackStackChanged() {
            toggle.setDrawerIndicatorEnabled(getSupportFragmentManager().getBackStackEntryCount() == 0);
        }
    });
}

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        super.onBackPressed();
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }
    switch (item.getItemId()) {
        // Respond to the action bar's Up/Home button
        case android.R.id.home:
            Toast.makeText(getApplicationContext(),"Back button clicked", Toast.LENGTH_SHORT).show();
            return true;
    }
    return super.onOptionsItemSelected(item);
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();
    TextView text = (TextView) findViewById(R.id.container_text);
    Fragment fragment = null;

    if (id == R.id.nav_about) {

        fragment = DemoFragment.newInstance("about");
        text.setText("1");
    }  else if (id == R.id.nav_settings) {

        fragment = DemoFragment.newInstance("nav settings");
    }
    getSupportFragmentManager()
            .beginTransaction()
            .replace(R.id.container, fragment)
            .addToBackStack(fragment.getClass().getSimpleName())
            .commit();

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}

CSS选择器 - 如何在选择器的事件中应用已定义的类

1 个答案: