android - 尝试在 android studio 上运行设备时出现 NullPointer 异常

Question

我是 android studio 的新手。在 android studio 上运行设备时出现 Nullpointer 异常。我正在为 arm 处理器使用 armeabi-v7a sdk。错误看起来像这样..

null
java.lang.NullPointerException
    at com.android.tools.idea.run.AndroidSessionInfo.isEmbeddable(AndroidSessionInfo.java:62)
    at com.android.tools.idea.run.AndroidRunConfigurationBase.getOldSessionTarget(AndroidRunConfigurationBase.java:307)
    at com.android.tools.idea.run.AndroidRunConfigurationBase.getState(AndroidRunConfigurationBase.java:279)
    at com.intellij.execution.runners.ExecutionEnvironment.getState(ExecutionEnvironment.java:201)
    at com.intellij.execution.runners.BaseProgramRunner.execute(BaseProgramRunner.java:58)
    at com.intellij.execution.runners.GenericProgramRunner.execute(GenericProgramRunner.java:31)
    at com.intellij.execution.runners.BaseProgramRunner.execute(BaseProgramRunner.java:53)
    at com.intellij.execution.runners.GenericProgramRunner.execute(GenericProgramRunner.java:31)
    at com.intellij.execution.ProgramRunnerUtil.executeConfiguration(ProgramRunnerUtil.java:94)
    at com.intellij.execution.impl.ExecutionManagerImpl.start(ExecutionManagerImpl.java:396)
    at com.intellij.execution.impl.ExecutionManagerImpl.access$400(ExecutionManagerImpl.java:61)
    at com.intellij.execution.impl.ExecutionManagerImpl$5.run(ExecutionManagerImpl.java:384)
    at com.intellij.util.concurrency.QueueProcessor.runSafely(QueueProcessor.java:238)
    at com.intellij.util.Alarm$Request$1.run(Alarm.java:351)
    at com.intellij.openapi.application.impl.LaterInvocator$FlushQueue.run(LaterInvocator.java:332)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
    at com.intellij.ide.IdeEventQueue.defaultDispatchEvent(IdeEventQueue.java:734)
    at com.intellij.ide.IdeEventQueue._dispatchEvent(IdeEventQueue.java:569)
    at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.java:382)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

list :

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.de34.myfirstapp">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

我的 gradle 看起来像:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.1"

    defaultConfig {
        applicationId "com.example.de34.myfirstapp"
        minSdkVersion 15
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    //testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.1.1'
    compile 'com.android.support:design:23.1.1'
}

主要 Activity 节点:

package com.example.de34.myfirstapp;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    @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();
            }
        });
    }

    @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_main, menu);
        return true;
    }

    public void OnclickMe(View view){
        Toast toast=Toast.makeText(this,"oh you clicked",Toast.LENGTH_LONG);
        toast.show();
    }
    @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);
    }
}

XML:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.example.de34.myfirstapp.MainActivity"
    tools:showIn="@layout/activity_main">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!click me if you dare"
        android:id="@+id/textView"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/clickMe"
        android:id="@+id/button"
        android:layout_marginTop="44dp"
        android:layout_below="@+id/textView"
        android:layout_centerHorizontal="true" />

</RelativeLayout>

Answer 1

你必须在布局文件中添加工具栏，如下所示

<include layout="@layout/app_bar"
    android:id="@+id/toolbar"/>

假设这是您的app_bar.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:contentInsetEnd="0dp"
    app:contentInsetStart="0dp"
    android:background="@color/blue"
    android:minHeight="?attr/actionBarSize">

<TextView

            android:id="@+id/toolbar_title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:text="My App Bar"
            android:textColor="@android:color/white"
            android:textSize="32sp"
            />
</android.support.v7.widget.Toolbar>