无法启动活动组件信息 java.lang.nullpointerexception 需要帮助吗？

Question

您好，我昨天刚开始学习在 android 上开发。我的应用程序在每次启动之前就停止了。

我做了一些研究，所以我查看了我的 logcat。这是我的日志：

FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myfirstapp/com.example.myfirstapp.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2295)
E/AndroidRuntime(26645):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)
E/AndroidRuntime(26645):    at android.app.ActivityThread.access$700(ActivityThread.java:159)
E/AndroidRuntime(26645):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
E/AndroidRuntime(26645):    at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(26645):    at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(26645):    at android.app.ActivityThread.main(ActivityThread.java:5419)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)

我有 1 节课：

package com.example.myfirstapp;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.splash);

        Thread logo = new Thread (){
            public void run(){
                try{
                    int logoTimer = 0;
                    while (logoTimer <= 5000){
                        sleep(100);
                        logoTimer = logoTimer + 100;
                    }
                    Intent startActivity = new Intent();
                    startActivity.setClassName("com.example.myfirstapp", "CLEARSCREEN");
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }finally{
                    finish();
                }
            }
        };
        getActionBar().hide();
        logo.run();
    }

    @Override
    protected void onDestroy() {
        // TODO Auto-generated method stub
        super.onDestroy();
    }

    @Override
    protected void onPause() {
        // TODO Auto-generated method stub
        super.onPause();
    }

    @Override
    protected void onRestart() {
        // TODO Auto-generated method stub
        super.onRestart();
    }

    @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
    }

    @Override
    protected void onStop() {
        // TODO Auto-generated method stub
        super.onStop();
    }
}

这是我的清单：

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

    <uses-sdk
        android:minSdkVersion="11"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@android:style/Theme.NoTitleBar">
        <activity
            android:name="com.example.myfirstapp.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>
    </application>

</manifest>

有什么方法可以从我的 logcat 中指出我的 NPE 在哪里？

提前非常感谢

Answer 1

---

您应该创建两个活动。第一个启动屏幕活动和第二个主要活动。我在您的清单文件中只看到一个。对 SecondActivity.class 使用意图。

更好地使用同步的安全方法编写代码，例如：

私有线程 mSplashThread;

@Override  
public void onCreate(Bundle savedInstanceState) {  
    super.onCreate(savedInstanceState);  

    setContentView(R.layout.splashscreen);  

    final SplashScreen sPlashScreen = this;     

    mSplashThread =  new Thread(){  
        @Override  
        public void run(){  
            try {  
                synchronized(this){  

                wait(3000);  
                }  
            }  
            catch(InterruptedException ex){                      
            }  

            finish();  

            Intent intent = new Intent();  
            intent.setClass(sPlashScreen, MainActivity.class);  
            startActivity(intent);  

        }  
    };  

    mSplashThread.start();          
}