我在Android Studio中从API 22更新到新版本24。 没有其他任何改变。但现在我遇到“setText”变量的问题。
错误：
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.app.something2156/com.app.something.webview.ModeratorPage}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
代码：
package com.app.something.webview;
import android.content.Intent;
import android.os.Bundle;
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.KeyEvent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings.PluginState;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.ProgressBar;
import android.widget.TextView;
import com.app.something.MainActivity;
import com.app.something.R;
import com.app.something.informations.WebradioConfig;
public class ModeratorPage extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {
WebView mWebView;
String URL = WebradioConfig.RadioModeratorURL;
ProgressBar loadingProgressBar, loadingTitle;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_webview_moderator);
TextView txtNavHeaderModeratorTitle = (TextView) findViewById(R.id.drawer_moderator_title);
txtNavHeaderModeratorTitle.setText("Text 01");
TextView txtNavHeaderModeratorDesc = (TextView) findViewById(R.id.drawer_moderator_desc);
txtNavHeaderModeratorDesc.setText("Text 02");
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
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);
mWebView = (WebView) findViewById(R.id.content_webview);
mWebView.getSettings().setJavaScriptEnabled(true);
mWebView.getSettings().setJavaScriptCanOpenWindowsAutomatically(true);
mWebView.getSettings().setPluginState(PluginState.ON);
mWebView.setScrollBarStyle(WebView.SCROLLBARS_OUTSIDE_OVERLAY);
mWebView.clearCache(true);
mWebView.loadUrl(URL);
mWebView.setWebViewClient(new MyWebViewClient());
loadingProgressBar = (ProgressBar) findViewById(R.id.progressbar_Horizontal);
mWebView.setWebChromeClient(new WebChromeClient() {
// this will be called on page loading progress
@Override
public void onProgressChanged(WebView view, int newProgress) {
super.onProgressChanged(view, newProgress);
loadingProgressBar.setProgress(newProgress);
//loadingTitle.setProgress(newProgress);
// hide the progress bar if the loading is complete
if (newProgress == 100) {
loadingProgressBar.setVisibility(View.VISIBLE);
} else {
loadingProgressBar.setVisibility(View.VISIBLE);
}
}
});
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (event.getAction() == KeyEvent.ACTION_DOWN) {
switch (keyCode) {
case KeyEvent.KEYCODE_BACK:
if (mWebView.canGoBack()) {
mWebView.goBack();
} else {
finish();
}
return true;
}
}
return super.onKeyDown(keyCode, event);
}
@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.menu_moderator, 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_home) {
Intent gonav_home = new Intent(getApplicationContext(), MainActivity.class);
startActivity(gonav_home);
return true;
}
if (id == R.id.action_sharing) {
Intent sendIntent = new Intent();
sendIntent.setAction(Intent.ACTION_SEND);
sendIntent.putExtra(Intent.EXTRA_TEXT, WebradioConfig.RadioSharingTextModeratorPage);
sendIntent.setType("text/plain");
startActivity(Intent.createChooser(sendIntent, WebradioConfig.RadioShareWithTitle));
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_home) {
Intent gonav_home = new Intent(getApplicationContext(), MainActivity.class);
startActivity(gonav_home);
} else if (id == R.id.nav_moderators) {
Intent gonav_moderators = new Intent(getApplicationContext(), ModeratorPage.class);
startActivity(gonav_moderators);
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
private class MyWebViewClient extends WebViewClient {
@Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
view.loadUrl(url);
return true;
}
}
}
以前没有问题。当我删除部分
TextView txtNavHeaderModeratorTitle = (TextView) findViewById(R.id.drawer_moderator_title);
txtNavHeaderModeratorTitle.setText("Text 01");
TextView txtNavHeaderModeratorDesc = (TextView) findViewById(R.id.drawer_moderator_desc);
txtNavHeaderModeratorDesc.setText("Text 02");
任何事情都有效，但这不能解决我的问题：（
activity_webview_moderator
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="start">
<include
layout="@layout/app_bar_webview"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<android.support.design.widget.NavigationView
android:id="@+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="@layout/nav_header_moderator"
app:menu="@menu/activity_main_drawer" />
</android.support.v4.widget.DrawerLayout>
nav_header_moderator
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="@dimen/nav_header_height"
android:background="@drawable/side_nav_bar"
android:gravity="top"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin_drawer"
android:paddingLeft="@dimen/activity_horizontal_margin_drawer"
android:paddingRight="@dimen/activity_horizontal_margin_drawer"
android:paddingTop="@dimen/activity_vertical_margin_drawer"
android:theme="@style/ThemeOverlay.AppCompat.Dark">
<TextView
android:id="@+id/drawer_moderator_title"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingTop="@dimen/nav_header_vertical_spacing"
android:singleLine="true"
android:textAppearance="@style/TextAppearance.AppCompat.Body1"
android:textColor="#ffffffff"
android:textSize="22.0sp"
android:textStyle="bold|italic" />
<TextView
android:id="@+id/drawer_moderator_desc"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ellipsize="marquee"
android:enabled="false"
android:gravity="center_vertical"
android:marqueeRepeatLimit="marquee_forever"
android:paddingLeft="2.0dip"
android:paddingRight="2.0dip"
android:textAppearance="?android:attr/textAppearanceLarge"
android:textColor="#ffffffff"
android:textSize="20.0sp" />
</LinearLayout>
希望有人可以帮助解决这个问题，谢谢。