不幸的是，appname已停止

时间：2015-06-20 16:53:28

标签： android android-activity android-radiogroup

我正在尝试创建一个启动mainActivity的简单android程序，当用户点击按钮时，secondActivity打开并显示一个带有三个单选按钮的无线电组。当用户点击单选按钮并按下按钮时，字符串传递给mainActivity，并且应该显示在textView On the mainActivity上。但当我按下主要活动按钮打开SecondActivity时。错误消息显示不幸的是，radioButtons已停止。我还更新了Manifest ..

这是我的代码：

mainActivity.java 

package com.example.radiobuttons;

import android.support.v4.widget.SimpleCursorAdapter.ViewBinder;
import android.support.v7.app.ActionBarActivity;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.TextView;
import android.view.View;


public class MainActivity extends Activity  {

    TextView txt1;
    Button b1;
    int requestCode = 12;

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

        Link();
        b1.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                Intent in = new Intent(MainActivity.this , secondActivity.class);
                startActivityForResult(in, requestCode);
            }
        });

    }

    public void Link()
    {
        txt1 = (TextView) findViewById(R.id.txtView1);
        b1 = (Button) findViewById(R.id.Button1);
    }



    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        // TODO Auto-generated method stub
        super.onActivityResult(requestCode, resultCode, data);
        if ( resultCode == 110){
        String txt = "Your Answer Is " +data.getStringExtra("answer");

        }

    }





}

secondActivity.java 

package com.example.radiobuttons;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.RadioGroup;
import android.widget.RadioGroup.OnCheckedChangeListener;

public class secondActivity extends Activity {

    RadioGroup rg;
    Button b1;
    String ans;
    Intent in;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.second);
        Link();

        rg.setOnCheckedChangeListener(new OnCheckedChangeListener() {

            @Override
            public void onCheckedChanged(RadioGroup group, int checkedId) {
                // TODO Auto-generated method stub

                switch (group.getId())
                {
                case R.id.radio0:
                    ans = "Manmohan Singh";

                    break;
                case R.id.radio1:
                    ans = "Mulayam Singh";
                    break;
                case R.id.radio2:
                    ans = "Narender Modi";
                    break;
                }

            }
        });

        b1.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                in = new Intent();
                in.putExtra("answer", ans);
                setResult(110,in);
                finish();
            }
        });
    }

    public void Link()
    {
        rg = (RadioGroup) findViewById(R.id.radioGroup1);
        b1 = (Button) findViewById(R.id.Button1);

    }
}

radioButtons Manifest 

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

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="21" />

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

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

</manifest>

logcat的：

06-20 12:44:05.319: E/AndroidRuntime(1905): FATAL EXCEPTION: main
06-20 12:44:05.319: E/AndroidRuntime(1905): Process: com.example.radiobuttons, PID: 1905
06-20 12:44:05.319: E/AndroidRuntime(1905): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.radiobuttons/com.example.radiobuttons.secondActivity}: java.lang.NullPointerException
06-20 12:44:05.319: E/AndroidRuntime(1905):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at android.os.Handler.dispatchMessage(Handler.java:102)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at android.os.Looper.loop(Looper.java:136)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at android.app.ActivityThread.main(ActivityThread.java:5001)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at java.lang.reflect.Method.invokeNative(Native Method)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at java.lang.reflect.Method.invoke(Method.java:515)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at dalvik.system.NativeStart.main(Native Method)
06-20 12:44:05.319: E/AndroidRuntime(1905): Caused by: java.lang.NullPointerException
06-20 12:44:05.319: E/AndroidRuntime(1905):     at com.example.radiobuttons.secondActivity.onCreate(secondActivity.java:47)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at android.app.Activity.performCreate(Activity.java:5231)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
06-20 12:44:05.319: E/AndroidRuntime(1905):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
06-20 12:44:05.319: E/AndroidRuntime(1905):     ... 11 more

activity_main.xml中

<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.radiobuttons.MainActivity" >

    <TextView
        android:id="@+id/txtView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />
    <Button
        android:id="@+id/Button1"
        android:layout_height="wrap_content"
        android:layout_width="fill_parent" 
        android:gravity="center_horizontal"
        android:layout_below="@+id/txtView1"
        android:text="Get Input From Second Activity" />

</RelativeLayout>

second.xml 

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/radioGroup1"
        android:layout_alignParentTop="true"
        android:layout_marginTop="17dp"
        android:text="Prime Minister Of India?" />

    <RadioGroup
        android:id="@+id/radioGroup1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_below="@+id/textView1"
        android:layout_marginLeft="30dp"
        android:layout_marginTop="21dp" >

        <RadioButton
            android:id="@+id/radio0"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"

            android:text="Manmohan Singh" />

        <RadioButton
            android:id="@+id/radio1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Mulayam Singh" />

        <RadioButton
            android:id="@+id/radio2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Narender Modi" />
    </RadioGroup>

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/radioGroup1"
        android:layout_below="@+id/radioGroup1"
        android:layout_marginTop="39dp"
        android:text="Submit Answer" />

</RelativeLayout>

2 个答案:

答案 0 :(得分：3)

你得到null pointer exception，因为你设置了错误的ID。在您的xml中，您提供了android:id="@+id/button1"，但您在Link（）中使用Button1。

答案 1 :(得分：0)

在Link()方法中，将按钮初始化更改为：

b1 = (Button) findViewById(R.id.button1);
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