在Android模拟器上运行时，我的应用程序正常运行，但在Android设备上运行时会崩溃。我看到它因ActionBar.setTitle()而崩溃，但错误是什么？发布主要活动，Logcat错误和构建Gradle的代码。
package com.example.mher.citygo;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.ListView;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
String[] items;
private static final int REQUEST_CALL=1;
ArrayList<String> listItems;
ArrayAdapter<String> adapter;
ListView listView;
EditText editText;
Button bregister;
private Toolbar toolbar;
ImageView help;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar=(Toolbar) findViewById(R.id.my_toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setTitle(null);
ArrayList<ItemData> list=new ArrayList<>();
list.add(new ItemData("Eng",R.drawable.usaflag));
list.add(new ItemData("Arm",R.drawable.armeniaflag));
list.add(new ItemData("Ru",R.drawable.russiaflag));
list.add(new ItemData("Per",R.drawable.iranflag));
final Button SearchARid=(Button) findViewById(R.id.bSearchRide);
Button LoginDriver=(Button) findViewById(R.id.bLogin_As_A_Driver);
bregister=(Button) findViewById(R.id.bRegister);
help=(ImageView) findViewById(R.id.help);
help.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent=new Intent(MainActivity.this,ActivityHelp.class);
start
Activity(intent);
overridePendingTransition( R.anim.slide_in_up,R.anim.stay);
}
});
bregister.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent SignUp=new Intent(MainActivity.this,RegisterActivity.class);
MainActivity.this.startActivity(SignUp);
}
});
LoginDriver.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent DriverLogin=new Intent(MainActivity.this,LoginActivity.class);
MainActivity.this.startActivity(DriverLogin);
}
});
SearchARid.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent SearchRide=new Intent(MainActivity.this, SearchRide.class);
MainActivity.this.startActivity(SearchRide);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater menuInflater=getMenuInflater();
menuInflater.inflate(R.menu.main_menu,menu);
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int res_id=item.getItemId();
if(res_id==R.id.actionSettings)
{
Intent intent=new Intent(MainActivity.this,SettingsActivity.class);
startActivity(intent);
overridePendingTransition(R.anim.right_to_left,R.anim.stay);
}
return super.onOptionsItemSelected(item);
}
}
这是我的Gradle（Mudule App）：
apply plugin: 'com.android.application'
android {
compileSdkVersion 25
buildToolsVersion "25.0.3"
defaultConfig {
applicationId "com.example.mher.citygo"
minSdkVersion 22
targetSdkVersion 25
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
exclude group: 'com.android.support', module: 'support-annotations'
})
compile 'com.android.support:appcompat-v7:25.3.1'
compile 'com.android.support:design:25.3.1'
compile 'com.android.support.constraint:constraint-layout:1.0.2'
compile 'com.google.firebase:firebase-database:9.2.1'
compile 'com.google.firebase:firebase-auth:9.2.1'
compile 'com.intuit.sdp:sdp-android:1.0.4'
testCompile 'junit:junit:4.12'
}
apply plugin: 'com.google.gms.google-services'
这是我的LogCat错误
08-11 20:27:00.404 21175-21175/com.example.mher.citygo E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.mher.citygo, PID: 21175
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mher.citygo/com.example.mher.citygo.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3256)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3352)
at android.app.ActivityThread.access$1100(ActivityThread.java:223)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1797)
**
**at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7231)
at java.lang.reflect.Method.invoke(Native Method)**
**
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
at com.example.mher.citygo.MainActivity.onCreate(MainActivity.java:39)
at android.app.Activity.performCreate(Activity.java:6877)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3209)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3352)
at android.app.ActivityThread.access$1100(ActivityThread.java:223)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1797)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7231)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
答案 0 :(得分：0)
答案 1 :(得分：0)
尝试关注而不是getSupportActionBar().setTitle(null)：
Field f = toolbar.getClass().getDeclaredField("mTitleTextView");
f.setAccessible(true);
TextView yourTextView = (TextView) f.get(toolbar);
yourTextView.setTitle("");