我正在加载一个简单的抽屉导航，里面有 3 个 fragment 。当我转到第一个 fragment 并单击该 fragment 中的一个按钮时，按钮的背景颜色会发生变化，然后我导航到第二个 fragment ，然后我又回到第一个 fragment ，我希望我的 fragment (带有颜色已更改的按钮)在后台.但它每次都会重新创建。我尝试了多种方法没有运气。由于我是 fragment 的新手，所以我坚持这一点。
public class SampleActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener, Fragment1.OnFragmentInteractionListener,
Fragment2.OnFragmentInteractionListener, Fragment3.OnFragmentInteractionListener {
static Fragment fragment = null;
private static final String FRAGMENT1_TAG = "FRAGMENT1_TAG";
private static final String FRAGMENT2_TAG = "FRAGMENT2_TAG";
private static final String FRAGMENT3_TAG = "FRAGMENT3_TAG";
@Override
public void onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) {
super.onSaveInstanceState(outState, outPersistentState);
}
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sample);
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
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);
}
@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.dashboard, 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;
}
return super.onOptionsItemSelected(item);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
int id = item.getItemId();
navigateToFragment(id);
return true;
}
@Override
public void onFragmentInteraction(Uri uri) {
}
public void navigateToFragment(int itemId) {
// Handle navigation view item clicks here.
String FRAGMENT_TAG="";
switch (itemId) {
case R.id.nav_fragment1:
FRAGMENT_TAG = FRAGMENT1_TAG;
fragment = Fragment1.newInstance();
break;
case R.id.nav_fragment2:
FRAGMENT_TAG = FRAGMENT2_TAG;
fragment = Fragment2.newInstance();
break;
case R.id.nav_fragment3:
FRAGMENT_TAG = FRAGMENT3_TAG;
fragment = Fragment3.newInstance();
break;
default:
FRAGMENT_TAG = FRAGMENT1_TAG;
fragment = Fragment1.newInstance();
break;
}
FragmentManager supportFragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = supportFragmentManager.beginTransaction();
Fragment inputFragment = supportFragmentManager.findFragmentByTag(FRAGMENT_TAG);
if (inputFragment == null) {
fragmentTransaction.replace(R.id.content_frame, fragment, FRAGMENT_TAG).addToBackStack(null).commit();
} else {
fragmentTransaction.replace(R.id.content_frame, inputFragment, FRAGMENT_TAG).addToBackStack(null).commit();
}
DrawerLayout drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
drawerLayout.closeDrawer(GravityCompat.START);
}
}
最佳答案
您应该添加 Fragment2.newInstance(); 的代码以更好地了解行为。
这段代码可能会解决您的问题:
public class SampleActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener, Fragment1.OnFragmentInteractionListener,
Fragment2.OnFragmentInteractionListener, Fragment3.OnFragmentInteractionListener {
static Fragment fragment1 = null;
static Fragment fragment2 = null;
static Fragment fragment3 = null;
private static final String FRAGMENT1_TAG = "FRAGMENT1_TAG";
private static final String FRAGMENT2_TAG = "FRAGMENT2_TAG";
private static final String FRAGMENT3_TAG = "FRAGMENT3_TAG";
@Override
public void onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) {
super.onSaveInstanceState(outState, outPersistentState);
}
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sample);
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
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);
}
@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.dashboard, 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;
}
return super.onOptionsItemSelected(item);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
int id = item.getItemId();
navigateToFragment(id);
return true;
}
@Override
public void onFragmentInteraction(Uri uri) {
}
public void navigateToFragment(int itemId) {
// Handle navigation view item clicks here.
String FRAGMENT_TAG="";
Fragment fragment = null;
switch (itemId) {
case R.id.nav_fragment2:
FRAGMENT_TAG = FRAGMENT2_TAG;
if(fragment2 == null) fragment2 = Fragment2.newInstance();
fragment = fragment2;
break;
case R.id.nav_fragment3:
FRAGMENT_TAG = FRAGMENT3_TAG;
if(fragment3 == null) fragment3 = Fragment3.newInstance();
fragment = fragment3;
break;
default:
FRAGMENT_TAG = FRAGMENT1_TAG;
if(fragment1 == null) fragment1 = Fragment1.newInstance();
fragment = fragment1;
break;
}
FragmentManager supportFragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = supportFragmentManager.beginTransaction();
Fragment inputFragment = supportFragmentManager.findFragmentByTag(FRAGMENT_TAG);
if (inputFragment == null) {
fragmentTransaction.replace(R.id.content_frame, fragment, FRAGMENT_TAG).addToBackStack(null).commit();
} else {
fragmentTransaction.replace(R.id.content_frame, inputFragment, FRAGMENT_TAG).addToBackStack(null).commit();
}
DrawerLayout drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
drawerLayout.closeDrawer(GravityCompat.START);
}
}
我建议您稍微重构一下代码以获得更优雅的解决方案。
请确保您是第一次使用 fragmentTransaction.add() 添加 fragment 。
关于android 抽屉导航每次都重新创建 fragment ，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/42761148/