我在android studio中创建了一个抽屉菜单并更改了抽屉的项目。我想在项目点击时启动另一个活动或查看另一个布局。但我得到以下错误，应用程序停止。
03-24 21:38:28.202 2227-10289/? D/GassUtils: Found app info for package com.example.imran.myapp:1. Hash: 6b9333e031907d7a6a6c12cd9fdfa0d23bd13ee0f40c9617ddd005dc358321b0
03-24 21:38:28.202 2227-10289/? D/k: Found info for package com.example.imran.myapp in db.
03-24 21:38:38.722 1035-1167/? V/ApplicationPolicy: isApplicationStateBlocked userId 0 pkgname com.example.imran.myapp
03-24 21:38:38.782 9789-9789/? I/Timeline: Timeline: Activity_launch_request id:com.example.imran.myapp time:121627337
03-24 21:38:38.802 1035-1853/? W/ActivityManager: NORMAL SET : srcAppInfo.processName = com.example.imran.myapp, destAppInfo.processName = com.example.imran.myapp
03-24 21:38:38.802 1035-1853/? W/ActivityManager: startActivity called from finishing ActivityRecord{28b176ac u0 com.example.imran.myapp/.MainActivity t2394 f}; forcing Intent.FLAG_ACTIVITY_NEW_TASK for: Intent { cmp=com.example.imran.myapp/.Home (has extras) }
03-24 21:38:38.802 1035-1853/? V/ApplicationPolicy: isApplicationStateBlocked userId 0 pkgname com.example.imran.myapp
03-24 21:38:39.402 1035-1532/? I/WindowManager: Switching to real app window: Window{11c67d3b u0 com.example.imran.myapp/com.example.imran.myapp.Home}
03-24 21:38:39.622 1035-1069/? I/Timeline: Timeline: Activity_windows_visible id: ActivityRecord{dca1b0 u0 com.example.imran.myapp/.Home t2396} time:121628177
03-24 21:38:58.462 9789-9789/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.imran.myapp, PID: 9789
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.widget.DrawerLayout.closeDrawer(int)' on a null object reference
at com.example.imran.myapp.Home.onNavigationItemSelected(Home.java:120)
at android.support.design.widget.NavigationView$1.onMenuItemSelected(NavigationView.java:146)
at android.support.v7.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:811)
at android.support.v7.internal.view.menu.SubMenuBuilder.dispatchMenuItemSelected(SubMenuBuilder.java:84)
at android.support.v7.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:153)
at android.support.v7.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:958)
at android.support.design.internal.NavigationMenuPresenter.onItemClick(NavigationMenuPresenter.java:196)
at android.widget.AdapterView.performItemClick(AdapterView.java:334)
at android.widget.AbsListView.performItemClick(AbsListView.java:1536)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3683)
at android.widget.AbsListView$3.run(AbsListView.java:5604)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6145)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
03-24 21:38:58.462 1035-1514/? V/ApplicationPolicy: isApplicationStateBlocked userId 0 pkgname com.example.imran.myapp
03-24 21:38:58.462 1035-1514/? W/ActivityManager: Force finishing activity com.example.imran.myapp/.Home
03-24 21:38:58.462 1035-1514/? V/ApplicationPolicy: isApplicationStateBlocked userId 0 pkgname com.example.imran.myapp
03-24 21:38:58.542 1035-1035/? D/CrashAnrDetector: processName: com.example.imran.myapp
03-24 21:38:58.542 1035-1035/? D/CrashAnrDetector: broadcastEvent : com.example.imran.myapp data_app_crash
03-24 21:38:58.992 1035-1062/? W/ActivityManager: Activity pause timeout for ActivityRecord{dca1b0 u0 com.example.imran.myapp/.Home t2396 f}
Java文件： Home.java
package com.example.imran.myapp;
import android.app.ProgressDialog;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.TextView;
public class Home extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
Button logout = (Button) findViewById(R.id.logout_button);
TextView text1 = (TextView) findViewById(R.id.result_sms);
final UserLocalStore loginuser = new UserLocalStore(getApplicationContext());
SharedPreferences mPrefs = getSharedPreferences("userDetails",0);
String str1=(mPrefs.getString("fullname","Default_Value"));
String email = loginuser.getLoggedInUser().email;
text1.setText("Welcome "+str1+"- Your email: "+email);
logout.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
loginuser.clearUserData();
//startActivity(new Intent(getApplicationContext(), MainActivity.class));
finish();
startActivity(new Intent(getApplicationContext(), MainActivity.class));
//setContentView(R.layout.activity_main);
}
});
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.home, 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) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_photos) {
// Handle the camera action
//setContentView(R.layout.myaccount);
} else if (id == R.id.nav_myaccount) {
setContentView(R.layout.activity_myaccount2);
//
} else if (id == R.id.nav_logout) {
UserLocalStore loginuser = new UserLocalStore(this);
loginuser.clearUserData();
finish();
startActivity(new Intent(getApplicationContext(), MainActivity.class));
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
在home.java的最后一部分，当我添加setContentView(R.layout.activity_myaccount2);
时，应用程序崩溃了。
答案 0 :(得分：1)
这里的问题是在调用drawer.closeDrawer();时出现空指针异常，正如您所说，在setContentView(R.layout.activity_myaccount2);被调用后会发生这种情况。
通过使用setContentView，您将整个布局替换为另一个布局，在这种情况下，您似乎将包含R.id.drawer_layout的布局替换为另一个不包含它的布局。当您尝试使用findViewById和closeDrawer时，当包含抽屉的布局不再存在时，会发生空指针异常，使用setContentView将其替换为另一个。
要解决此问题，您可能需要重新考虑如何构建应用并显示不同的内容。作为一个起点，我建议使用包含您的抽屉和片段的活动来查找示例，以显示不同的内容。活动和抽屉始终存在，只有片段发生变化，如this tutorial。