Question

我正在Android Studio中开展多项活动的应用，我正在尝试将button1转到 SecondActivity ，将button2转到我的 < EM> ThirdActivity 即可。每当我在我的应用程序中运行按钮时，它都会崩溃。

这是我的 MainActivity.java：

package hobby_pc.medispeak;

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

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button button1 = (Button) findViewById(R.id.button1);
    Button button2 = (Button) findViewById(R.id.button2);
    button1.setOnClickListener (new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            goToSecondActivity();
        }
    });

    button2.setOnClickListener (new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            goToThirdActivity();
        }
    });


        }
private void goToSecondActivity()
{
    Intent intent = new Intent(this, SecondActivity.class);
    startActivity(intent);

}
private void goToThirdActivity()
{
    Intent intent = new Intent(this, ThirdActivity.class);
    startActivity(intent);

}

这是我的 activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<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="hobby_pc.medispeak.MainActivity"
android:background="#ffffff">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/Welkom"
    android:textSize="@dimen/abc_text_size_title_material_toolbar"
    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/Medicijnenzoeken"
    android:id="@+id/button1"
    android:layout_marginTop="111dp"
    android:layout_below="@+id/textView"
    android:layout_centerHorizontal="true" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Goochempie"
    android:id="@+id/button2"
    android:layout_below="@+id/button1"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="72dp" />


</RelativeLayout>

这是我的 AndroidManifest.xml：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="hobby_pc.medispeak">
<uses-permission android:name="android.permission.WAKE_LOCK"></uses-permission>
<uses-permission android:name="android.permission.INTERNET" />

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:largeHeap="true"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity
        android:name=".SplashScreen"
        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=".MainActivity"
        android:label="@string/app_name">
        <intent-filter>
            <action android:name="com.Medispeak.androidsplashscreenexample.MAINACTIVITY" />
        </intent-filter>
    </activity>

    <category android:name="android.intent.category.DEFAULT" />
    <activity android:name=".ThirdActivity" />
    <activity android:name=".SecondActivity" />
    <receiver android:name=".AlarmReceiver"></receiver>
</application>

这是我崩溃时遇到的错误：

06-02 14:13:25.900 21384-21384/hobby_pc.medispeak E/AndroidRuntime: FATAL EXCEPTION: main
Process: hobby_pc.medispeak, PID: 21384
    java.lang.RuntimeException: Unable to start activity ComponentInfo{hobby_pc.medispeak/hobby_pc.medispeak.ThirdActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2702)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2767)
    at android.app.ActivityThread.access$900(ActivityThread.java:177)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1449)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:145)
    at android.app.ActivityThread.main(ActivityThread.java:5951)
    at java.lang.reflect.Method.invoke(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:372)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1400)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195)
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at hobby_pc.medispeak.ThirdActivity.onCreate(ThirdActivity.java:34)
    at android.app.Activity.performCreate(Activity.java:6289)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2655)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2767) 
    at android.app.ActivityThread.access$900(ActivityThread.java:177) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1449) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:145) 
    at android.app.ActivityThread.main(ActivityThread.java:5951) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:372) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1400) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195)

Answer 1

您似乎未在 AndroidManifest.xml 中声明 ThirdActivity 。

Answer 2

你可以在这一行看到崩溃原因：java.lang.RuntimeException：无法启动活动ComponentInfo {hobby_pc.medispeak / hobby_pc.medispeak.ThirdActivity}：java.lang.NullPointerException：尝试调用虚方法＆＃39 ; void android.widget.TextView.setText（java.lang.CharSequence）＆＃39;在空对象引用上

我认为在thirdActivity中的onCreate方法中，您正在尝试为未绑定查看的textView设置setText。在textView

上调用setText（）之前使用findViewById（）

Answer 3

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at hobby_pc.medispeak.ThirdActivity.onCreate(ThirdActivity.java:34)

你的问题是，你的NullPointerException课程中的ThirdActivity位于第34行。您显然在setText()上调用了TextView而未使用findViewById(R.id.some_id)进行初始化第一

添加2个按钮以链接到Android Studio中的2个不同活动

3 个答案: