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[英]How do I call a non-static method from another class in a non-static method? (java)
[英]How to call non-static method from another class in an Android Application
因此,一旦在Android应用程序中点击了某个项目,我就会尝试调用一个方法。
这是我要调用的方法是getFavourites();
public class Favourites extends Activity {
public void getFavourites(){
ViewFlipper viewFlipper = (ViewFlipper) findViewById(R.id.viewFlipper);
viewFlipper.setDisplayedChild(0);
setTitle("Favourites");
}
}
这是我要调用方法getFavourtites();
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_favourite) {
Favourites getFav = new Favourites();
getFav.getFavourites();
} else if (id == R.id.nav_search) {
ViewFlipper viewFlipper = (ViewFlipper) findViewById(R.id.viewFlipper);
viewFlipper.setDisplayedChild(1);
setTitle("Search");
} else if (id == R.id.nav_share) {
} else if (id == R.id.nav_sendFeedback) {
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
我真的不知道自己在做什么错,但是每次运行它时,应用程序都会崩溃。
编辑:这是收藏夹的完整堆栈
package com.ctt.mrdan.croydontramtime2;
import android.app.Activity;
import android.widget.ViewFlipper;
/**
* Created by MrDan on 16/07/2016.
*/
public class Favourites extends Activity {
public void getFavourites(){
ViewFlipper viewFlipper = (ViewFlipper) findViewById(R.id.viewFlipper);
viewFlipper.setDisplayedChild(0);
setTitle("Favourites");
}
}
这是Main的完整堆栈
package com.ctt.mrdan.croydontramtime2;
import android.content.Intent;
import android.os.Bundle;
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.ViewFlipper;
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);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
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.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;
}
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_favourite) {
Favourites getFav = new Favourites();
getFav.getFavourites();
} else if (id == R.id.nav_search) {
ViewFlipper viewFlipper = (ViewFlipper) findViewById(R.id.viewFlipper);
viewFlipper.setDisplayedChild(1);
setTitle("Search");
} else if (id == R.id.nav_share) {
} else if (id == R.id.nav_sendFeedback) {
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
您要实例化Favourites
,然后在新实例上调用getFavourites()
。 getFavourites()
调用findViewById()
,该方法隐式调用getWindow().findViewById()
,但是Activity
没有内容视图,从而导致NullPointerException
。
Favourites
根本没有目的。
您可以将代码从getFavourites()
移到onNavigationItemSelected()
:
viewFlipper = (ViewFlipper) findViewById(R.id.viewFlipper);
// ...
if (id == R.id.nav_favourite) {
viewFlipper.setDisplayedChild(0);
setTitle("Favourites");
} else if (id == R.id.nav_search) {
viewFlipper.setDisplayedChild(1);
setTitle("Search");
}
另外,您永远不要使用new
关键字实例化一个Activity
。 使用Intent
并将实例化留给ActivityManager
。
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