private void SwitchFra(Fragment fr){
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
//如果要切换的fragment没有添加则添加
if(!fr.isAdded()){
ft.add(R.id.dl_cebian,fr);
//如果要被切换的fragment不是空的,则隐藏
if (lastFra != null) {
ft.hide(lastFra);
}
} else { //否则隐藏上一个fragment,显示要切换的fragment
ft.hide(lastFra)
.show(fr);
}
lastFra = fr;
//提交
ft.commit();
}
//监听
navCehua.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
switch (menuItem.getItemId()) {
case R.id.it_Upload:
tvTitle.setText("上传错题");
SwitchFra(fr_u);
Toast.makeText(MainActivity.this,menuItem.getTitle().toString(),Toast.LENGTH_SHORT).show();
break;
case R.id.it_Calendar:
tvTitle.setText("考试月历");
SwitchFra(fr_c);
break;
case R.id.it_Text:
tvTitle.setText("错题测试");
SwitchFra(fr_t);
Toast.makeText(MainActivity.this,menuItem.getTitle().toString(),Toast.LENGTH_SHORT).show();
break;
case R.id.it_Analyse:
tvTitle.setText("图谱分析");
SwitchFra(fr_a);
break;
}
// Toast.makeText(MainActivity.this,"只执行",Toast.LENGTH_SHORT).show();
DrawerLayout drawer = (DrawerLayout)findViewById(R.id.dl_cebian);
drawer.closeDrawer(GravityCompat.START);
return true;
}
});}```