使用startActivityForResult时应用程序崩溃

debugcn 发表于 Dev

字母代码

我在2类“ MainActivity”和“ abc”类之间使用startActivityForResult。我遇到的问题是应用程序在启动时不断崩溃，并且通过阅读LogCat我认为崩溃是由于MainActivity类中的NPE“ NullPointException”（但我不确定）。我已经寻找了数小时的解决方案，但找不到解决我的情况的解决方案。

1）MainActivity类：

package com.example.passstrings;


import android.support.v7.app.ActionBarActivity;
import android.support.v4.app.Fragment;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends ActionBarActivity {
Button bt1;
TextView tv2;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

      tv2 = (TextView) findViewById(R.id.textView2);
      bt1=(Button) findViewById(R.id.button1);
    bt1.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                Intent intent = new Intent(MainActivity.this , abc.class);
                startActivityForResult(intent , 0);

            }
    });



        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment())
                    .commit();
        }
    }

@Override
protected void onActivityResult(int requestCode , int resultCode , Intent data){
    super.onActivityResult(requestCode, resultCode, data);
    if (resultCode == RESULT_OK){
        Intent intent = getIntent();
        String pass= intent.getExtras().getString("key");
        tv2.setText(pass);
        }

}

    @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();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);
            return rootView;
        }
    }

}

2）abc类

package com.example.passstrings;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.TextView;

public class abc extends Activity{
TextView tv1;
String setData;
RadioButton r1,r2,r3,r4;
Button bt2;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.abc);
        r1 = (RadioButton) findViewById(R.id.radioButton1);
        r2 = (RadioButton) findViewById(R.id.RadioButton01);
        r3 = (RadioButton) findViewById(R.id.RadioButton02);
        r4 = (RadioButton) findViewById(R.id.RadioButton03);
        bt2.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                 if (r1.isChecked() || r2.isChecked() || r3.isChecked() == true){
                        setData ="Failed";
                    }else if (r3.isChecked() ==true){
                        setData="Passed";
                    }else{
                        setData="You didn't choose an answer";
                    }
                    Intent Int = new Intent(abc.this , MainActivity.class);
                    Int.putExtra("key", setData);
                    setResult(RESULT_OK , Int);
                     finish();






                        }

});
    }
}

3）LogCat：

04-04 14:52:15.406: I/dalvikvm(369): Could not find method android.content.pm.PackageManager.getActivityLogo, referenced from method android.support.v7.internal.widget.ActionBarView.<init>
04-04 14:52:15.415: W/dalvikvm(369): VFY: unable to resolve virtual method 320: Landroid/content/pm/PackageManager;.getActivityLogo (Landroid/content/ComponentName;)Landroid/graphics/drawable/Drawable;
04-04 14:52:15.415: D/dalvikvm(369): VFY: replacing opcode 0x6e at 0x008b
04-04 14:52:15.415: I/dalvikvm(369): Could not find method android.content.pm.ApplicationInfo.loadLogo, referenced from method android.support.v7.internal.widget.ActionBarView.<init>
04-04 14:52:15.415: W/dalvikvm(369): VFY: unable to resolve virtual method 316: Landroid/content/pm/ApplicationInfo;.loadLogo (Landroid/content/pm/PackageManager;)Landroid/graphics/drawable/Drawable;
04-04 14:52:15.415: D/dalvikvm(369): VFY: replacing opcode 0x6e at 0x0099
04-04 14:52:15.425: D/dalvikvm(369): VFY: dead code 0x008e-0092 in Landroid/support/v7/internal/widget/ActionBarView;.<init> (Landroid/content/Context;Landroid/util/AttributeSet;)V
04-04 14:52:15.425: D/dalvikvm(369): VFY: dead code 0x009c-00a0 in Landroid/support/v7/internal/widget/ActionBarView;.<init> (Landroid/content/Context;Landroid/util/AttributeSet;)V
04-04 14:52:15.535: D/AndroidRuntime(369): Shutting down VM
04-04 14:52:15.535: W/dalvikvm(369): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
04-04 14:52:15.545: E/AndroidRuntime(369): FATAL EXCEPTION: main
04-04 14:52:15.545: E/AndroidRuntime(369): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.passstrings/com.example.passstrings.MainActivity}: java.lang.NullPointerException
04-04 14:52:15.545: E/AndroidRuntime(369):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
04-04 14:52:15.545: E/AndroidRuntime(369):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
04-04 14:52:15.545: E/AndroidRuntime(369):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
04-04 14:52:15.545: E/AndroidRuntime(369):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
04-04 14:52:15.545: E/AndroidRuntime(369):  at android.os.Handler.dispatchMessage(Handler.java:99)
04-04 14:52:15.545: E/AndroidRuntime(369):  at android.os.Looper.loop(Looper.java:123)
04-04 14:52:15.545: E/AndroidRuntime(369):  at android.app.ActivityThread.main(ActivityThread.java:4627)
04-04 14:52:15.545: E/AndroidRuntime(369):  at java.lang.reflect.Method.invokeNative(Native Method)
04-04 14:52:15.545: E/AndroidRuntime(369):  at java.lang.reflect.Method.invoke(Method.java:521)
04-04 14:52:15.545: E/AndroidRuntime(369):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
04-04 14:52:15.545: E/AndroidRuntime(369):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
04-04 14:52:15.545: E/AndroidRuntime(369):  at dalvik.system.NativeStart.main(Native Method)
04-04 14:52:15.545: E/AndroidRuntime(369): Caused by: java.lang.NullPointerException
04-04 14:52:15.545: E/AndroidRuntime(369):  at com.example.passstrings.MainActivity.onCreate(MainActivity.java:26)
04-04 14:52:15.545: E/AndroidRuntime(369):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-04 14:52:15.545: E/AndroidRuntime(369):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
04-04 14:52:15.545: E/AndroidRuntime(369):  ... 11 more

4）abc.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    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">

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="23dp"
        android:text="Which of the following vitamins helps clotting the blood : "
        android:textSize="30sp" />

    <RadioButton
        android:id="@+id/radioButton1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/textView2"
        android:layout_below="@+id/textView2"
        android:layout_marginLeft="62dp"
        android:layout_marginTop="14dp"
        android:text="Vitamin A" />

    <RadioButton
        android:id="@+id/RadioButton03"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/RadioButton01"
        android:layout_alignParentBottom="true"
        android:layout_marginBottom="60dp"
        android:text="None Of Above" />

    <RadioButton
        android:id="@+id/RadioButton01"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/RadioButton03"
        android:layout_alignRight="@+id/RadioButton02"
        android:layout_marginBottom="26dp"
        android:text="Vitamin C" />

    <RadioButton
        android:id="@+id/RadioButton02"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/radioButton1"
        android:layout_below="@+id/radioButton1"
        android:layout_marginTop="16dp"
        android:text="Vitamin D" />

    <Button
        android:id="@+id/button1"
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:text="Check"
        android:textSize="30sp" />

</RelativeLayout>

5）fragment_main.xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    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"
        tools:context="com.example.ytdownload.MainActivity$PlaceholderFragment" >

    >

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="23dp"
        android:text="Click Below to start the test . Please only choose on of the answers"
        android:textSize="30sp" />

    <Button
        android:id="@+id/button1"
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView2"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="74dp"
        android:text="Start"
        android:textSize="30sp" />

</RelativeLayout>

6）清单：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.passstrings"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="19" />

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

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

</manifest>

7）activity_main.xml：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:ignore="MergeRootFrame" 

    tools:context="com.example.passstrings.MainActivity$PlaceholderFragment" >

    >


</FrameLayout>

如果我将MainActivity中的setContentView更改为fragment，则会在LogCat中显示此错误“尽管将其设置为activity_main并编辑fragment_main总是对我有用”

04-04 15:13:42.995: I/dalvikvm(592): Could not find method android.content.pm.PackageManager.getActivityLogo, referenced from method android.support.v7.internal.widget.ActionBarView.<init>
04-04 15:13:42.995: W/dalvikvm(592): VFY: unable to resolve virtual method 320: Landroid/content/pm/PackageManager;.getActivityLogo (Landroid/content/ComponentName;)Landroid/graphics/drawable/Drawable;
04-04 15:13:42.995: D/dalvikvm(592): VFY: replacing opcode 0x6e at 0x008b
04-04 15:13:42.995: I/dalvikvm(592): Could not find method android.content.pm.ApplicationInfo.loadLogo, referenced from method android.support.v7.internal.widget.ActionBarView.<init>
04-04 15:13:42.995: W/dalvikvm(592): VFY: unable to resolve virtual method 316: Landroid/content/pm/ApplicationInfo;.loadLogo (Landroid/content/pm/PackageManager;)Landroid/graphics/drawable/Drawable;
04-04 15:13:42.995: D/dalvikvm(592): VFY: replacing opcode 0x6e at 0x0099
04-04 15:13:43.006: D/dalvikvm(592): VFY: dead code 0x008e-0092 in Landroid/support/v7/internal/widget/ActionBarView;.<init> (Landroid/content/Context;Landroid/util/AttributeSet;)V
04-04 15:13:43.006: D/dalvikvm(592): VFY: dead code 0x009c-00a0 in Landroid/support/v7/internal/widget/ActionBarView;.<init> (Landroid/content/Context;Landroid/util/AttributeSet;)V
04-04 15:13:43.135: E/FragmentManager(592): No view found for id 0x7f050042 (com.example.passstrings:id/container) for fragment PlaceholderFragment{4a310490 #0 id=0x7f050042}
04-04 15:13:43.135: E/FragmentManager(592): Activity state:
04-04 15:13:43.135: D/FragmentManager(592):   Local FragmentActivity 4a2f4ae8 State:
04-04 15:13:43.135: D/FragmentManager(592):     mCreated=truemResumed=false mStopped=false mReallyStopped=false
04-04 15:13:43.135: D/FragmentManager(592):     mLoadersStarted=false
04-04 15:13:43.135: D/FragmentManager(592):   Active Fragments in 4a2f5aa8:
04-04 15:13:43.135: D/FragmentManager(592):     #0: PlaceholderFragment{4a310490 #0 id=0x7f050042}
04-04 15:13:43.151: D/FragmentManager(592):       mFragmentId=#7f050042 mContainerId=#7f050042 mTag=null
04-04 15:13:43.151: D/FragmentManager(592):       mState=0 mIndex=0 mWho=android:fragment:0 mBackStackNesting=0
04-04 15:13:43.155: D/FragmentManager(592):       mAdded=true mRemoving=false mResumed=false mFromLayout=false mInLayout=false
04-04 15:13:43.155: D/FragmentManager(592):       mHidden=false mDetached=false mMenuVisible=true mHasMenu=false
04-04 15:13:43.155: D/FragmentManager(592):       mRetainInstance=false mRetaining=false mUserVisibleHint=true
04-04 15:13:43.155: D/FragmentManager(592):       mFragmentManager=FragmentManager{4a2f5aa8 in MainActivity{4a2f4ae8}}
04-04 15:13:43.155: D/FragmentManager(592):       mActivity=com.example.passstrings.MainActivity@4a2f4ae8
04-04 15:13:43.155: D/FragmentManager(592):   Added Fragments:
04-04 15:13:43.165: D/FragmentManager(592):     #0: PlaceholderFragment{4a310490 #0 id=0x7f050042}
04-04 15:13:43.165: D/FragmentManager(592):   FragmentManager misc state:
04-04 15:13:43.165: D/FragmentManager(592):     mActivity=com.example.passstrings.MainActivity@4a2f4ae8
04-04 15:13:43.165: D/FragmentManager(592):     mContainer=android.support.v4.app.FragmentActivity$2@4a2f63b0
04-04 15:13:43.165: D/FragmentManager(592):     mCurState=2 mStateSaved=false mDestroyed=false
04-04 15:13:43.165: D/FragmentManager(592):   View Hierarchy:
04-04 15:13:43.165: D/FragmentManager(592):     com.android.internal.policy.impl.PhoneWindow$DecorView{4a2f9690 V.E..... ... 0,0-0,0}
04-04 15:13:43.175: D/FragmentManager(592):       android.widget.FrameLayout{4a2f9fd0 V.ED.... ... 0,0-0,0}
04-04 15:13:43.175: D/FragmentManager(592):         android.widget.LinearLayout{4a2facf0 V.E..... ... 0,0-0,0}
04-04 15:13:43.175: D/FragmentManager(592):           android.support.v7.internal.widget.ActionBarContainer{4a2fb788 V.ED.... ... 0,0-0,0 #7f050021 app:id/action_bar_container}
04-04 15:13:43.175: D/FragmentManager(592):             android.support.v7.internal.widget.ActionBarView{4a304150 V.E..... ... 0,0-0,0 #7f050022 app:id/action_bar}
04-04 15:13:43.175: D/FragmentManager(592):               android.widget.LinearLayout{4a308a98 G.....C. ... 0,0-0,0}
04-04 15:13:43.175: D/FragmentManager(592):                 android.widget.ImageView{4a3093e8 G.ED.... ... 0,0-0,0 #7f050027 app:id/up}
04-04 15:13:43.175: D/FragmentManager(592):                 android.widget.LinearLayout{4a309618 V.E..... ... 0,0-0,0}
04-04 15:13:43.187: D/FragmentManager(592):                   android.widget.TextView{4a309a98 V.ED.... ... 0,0-0,0 #7f050028 app:id/action_bar_title}
04-04 15:13:43.187: D/FragmentManager(592):                   android.widget.TextView{4a30acd8 G.ED.... ... 0,0-0,0 #7f050029 app:id/action_bar_subtitle}
04-04 15:13:43.187: D/FragmentManager(592):               android.support.v7.internal.widget.ActionBarView$HomeView{4a305088 VFE...C. ... 0,0-0,0}
04-04 15:13:43.187: D/FragmentManager(592):                 android.widget.ImageView{4a307388 G.ED.... ... 0,0-0,0 #7f050027 app:id/up}
04-04 15:13:43.187: D/FragmentManager(592):                 android.widget.ImageView{4a3078e8 V.ED.... ... 0,0-0,0 #7f050014 app:id/home}
04-04 15:13:43.198: D/FragmentManager(592):             android.support.v7.internal.widget.ActionBarContextView{4a30b6a8 G.E..... ... 0,0-0,0 #7f050023 app:id/action_context_bar}
04-04 15:13:43.198: D/FragmentManager(592):           android.widget.FrameLayout{4a30c040 V.ED.... ... 0,0-0,0 #1020002 android:id/content}
04-04 15:13:43.198: D/FragmentManager(592):             android.widget.RelativeLayout{4a30d688 V.E..... ... 0,0-0,0}
04-04 15:13:43.205: D/FragmentManager(592):               android.widget.TextView{4a30db18 V.ED.... ... 0,0-0,0 #7f05001a app:id/textView2}
04-04 15:13:43.205: D/FragmentManager(592):               android.widget.Button{4a30e368 VFED..C. ... 0,0-0,0 #7f05001f app:id/button1}
04-04 15:13:43.205: D/FragmentManager(592):           android.support.v7.internal.widget.ActionBarContainer{4a30c2e8 G.ED.... ... 0,0-0,0 #7f050024 app:id/split_action_bar}
04-04 15:13:43.205: D/AndroidRuntime(592): Shutting down VM
04-04 15:13:43.205: W/dalvikvm(592): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
04-04 15:13:43.215: E/AndroidRuntime(592): FATAL EXCEPTION: main
04-04 15:13:43.215: E/AndroidRuntime(592): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.passstrings/com.example.passstrings.MainActivity}: java.lang.IllegalArgumentException: No view found for id 0x7f050042 (com.example.passstrings:id/container) for fragment PlaceholderFragment{4a310490 #0 id=0x7f050042}
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.os.Handler.dispatchMessage(Handler.java:99)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.os.Looper.loop(Looper.java:123)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.app.ActivityThread.main(ActivityThread.java:4627)
04-04 15:13:43.215: E/AndroidRuntime(592):  at java.lang.reflect.Method.invokeNative(Native Method)
04-04 15:13:43.215: E/AndroidRuntime(592):  at java.lang.reflect.Method.invoke(Method.java:521)
04-04 15:13:43.215: E/AndroidRuntime(592):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
04-04 15:13:43.215: E/AndroidRuntime(592):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
04-04 15:13:43.215: E/AndroidRuntime(592):  at dalvik.system.NativeStart.main(Native Method)
04-04 15:13:43.215: E/AndroidRuntime(592): Caused by: java.lang.IllegalArgumentException: No view found for id 0x7f050042 (com.example.passstrings:id/container) for fragment PlaceholderFragment{4a310490 #0 id=0x7f050042}
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:930)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1115)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1478)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:570)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1129)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.app.Activity.performStart(Activity.java:3781)
04-04 15:13:43.215: E/AndroidRuntime(592):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2636)
04-04 15:13:43.215: E/AndroidRuntime(592):  ... 11 more

阿尔文·贝纳（Alvin Baena）

这NullPointerException是因为您尝试在activity_main.xml中查找R.id.textView2和R.id.button1，并且这些ID不存在。

如果您仔细查看日志，则会有一行显示NPE发生的位置，在您的情况下，该行是：

04-04 14:52:15.545: E/AndroidRuntime(369): Caused by: java.lang.NullPointerException
04-04 14:52:15.545: E/AndroidRuntime(369):  at com.example.passstrings.MainActivity.onCreate(MainActivity.java:26)

如您所见，在类的第26行中MainActivity.java，特别onCreate()是在发生错误的方法中，我几乎可以肯定该错误是由xml中缺少ID引起的。为了解决这个问题，您必须将Buttonand和TextView在代码（R.id.textView2和R.id.button1）中指定的ID放入main_activity.xml中。

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编辑于2021-06-6

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