我正在加载一个带有3个片段的简单导航抽屉。当我转到第一个片段并单击该片段中的一个按钮然后按钮背景颜色被更改然后我导航到第二个片段再次我回到第一个片段我想要我的片段（带有颜色更改按钮）在后台。但它每次都会重新创建。我试过多种方法没有运气。因为我是片段新手，所以我坚持这个。
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);
}
}
答案 0 :(得分：1)
您应该添加Fragment2.newInstance();的代码以更好地了解行为。
此代码可能解决您的问题：
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);
}
}
我建议您重构一下代码以获得更优雅的解决方案。
请确保您第一次使用fragmentTransaction.add()添加片段。
答案 1 :(得分：0)
使用堆栈跟踪片段。 请查看以下链接以供参考。
https://github.com/rathodchintan/Fragment-Back-Stack
1.如果您不想重新加载片段，请不要使用替换方法。 相反，它使用add方法将片段对象保留在堆栈中。