Android Activity在启动时崩溃

Question

I can't understand why my app crashes when I try to change Activity .

Here is the manifest file:

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

<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">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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

Here is the MainActivity file:

package com.example.android.testsubject;

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.activity_main);
    }

    private void switchTo1(View view){
        Intent intentTo2 = new Intent(MainActivity.this, SecondActivity.class);
        startActivity(intentTo2);
    }
}

SecondActivity file:

package com.example.android.testsubject;

import android.os.Bundle;
import android.view.View;

public class SecondActivity extends MainActivity {

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

    public void switchTo2(View view){}

}

activity_main.xml file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    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"
    android:orientation="vertical"
    android:gravity="center_horizontal"
    tools:context="com.example.android.testsubject.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="This, is screen 1"
        android:layout_marginBottom="16sp" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Here we go to the second screen"
        android:onClick="switchTo1" />

</LinearLayout>

second_activity_layout.xml file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16sp"
    android:gravity="center_horizontal"
    android:background="#FFFF00">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="This, is screen 2"
        android:layout_marginBottom="16sp" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Here we go to the first screen"
        android:onClick="switchTo2" />

</LinearLayout>

Answer 1

switchTo1(View view) has a private access modifier and cannot be accesed outside of the class. Make it public :

public void switchTo1(View view)

Answer 2

 private void switchTo1(View view){}  

将其更改为公开，以允许班级外部访问