Question

我在我的主要活动上做了一个按钮，该按钮应该打开另一个活动。我在AndroidManifest.xml中声明了活动，函数看起来像这样：

package com.example.cristian.befficient;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.layout.activity_main);
}

public void addact(View v)
{
    startActivity(new Intent(MainActivity.this, NewAct.class));
}

错误与操作栏有关，我该如何解决？崩溃日志：

--------- beginning of crash
E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.example.cristian.befficient, PID: 2299
              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.cristian.befficient/com.example.cristian.befficient.NewAct}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
                  at android.app.ActivityThread.-wrap12(ActivityThread.java)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
                  at android.os.Handler.dispatchMessage(Handler.java:102)
                  at android.os.Looper.loop(Looper.java:154)
                  at android.app.ActivityThread.main(ActivityThread.java:6077)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
                  at com.example.cristian.befficient.NewAct.onCreate(NewAct.java:12)
                  at android.app.Activity.performCreate(Activity.java:6664)
                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
                  at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 
                  at android.os.Handler.dispatchMessage(Handler.java:102) 
                  at android.os.Looper.loop(Looper.java:154) 
                  at android.app.ActivityThread.main(ActivityThread.java:6077) 
                  at java.lang.reflect.Method.invoke(Native Method) 
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

申请已终止。

我要打开的活动：

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.NestedScrollView       
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.cristian.befficient.NewAct">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_margin="@dimen/text_margin"
    android:text="@string/large_text" />

是的，它已在清单文件

中声明

<activity
        android:name=".NewAct"
        android:label="@string/title_activity_new"
        android:parentActivityName=".MainActivity">
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.example.cristian.befficient.MainActivity" />
    </activity>

Answer 1

转到构建并按清洁项目。（构建 - ＆gt;清洁项目）这有助于您解决无法恢复符号'R'错误

Answer 2

使用

import com.example.cristian.befficient.R;

鉴于com.example.cristian.befficient是应用程序的包。

Answer 3

在 NewAct 行 12

中使用445653代替supportActionBar

Answer 4

操作栏错误

使用getSupportActionBar()代替getActionBar()
public class NewAct extends AppCompatActivity

Answer 5

无论出于何种原因，您的操作栏可能为空。检查主要活动的样式，并确保已启用操作栏。

检查你的 - values / styles.xml并确保它有一个操作栏。

<style name = "AppTheme" parent = "android:Theme.Holo.Light.DarkActionBar">
    <!-- Customize your theme here. -->
</style>

请查看此链接以获取更多信息https://developer.android.com/design/patterns/actionbar.html

按下按钮打开新活动时，应用程序崩溃

5 个答案: