Java RuntimeException:无法实例化活动组件信息Android

我试图用android编写一些代码，但我无法在我的外部设备上运行。它总是被迫退出。我已经在android中编写了一两个代码，我总是能够启动它们，所以我不知道这个错误是从哪里来的

这是启动器活动的代码：

package x.y.alarm;

import java.util.ArrayList;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends ActionBarActivity {

    final int setAlarm = 214;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button add = (Button) findViewById(R.id.add);
        add.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                startActivityForResult(new Intent(MainActivity.this,AlarmScreen.class), setAlarm);
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data){
        if(requestCode == setAlarm){
            if(resultCode == RESULT_OK){
                String name = data.getStringExtra("Name");
                String time = data.getStringExtra("Time");  //In h:m format
                String days = data.getStringExtra("Days");  //Seperated by ;

                String[] t = time.split(":");
                String[] d = days.split(";");

                int[] hrsAndMin = new int[t.length];
                for(int i = 0; i < t.length; i++){
                    hrsAndMin[i] = Integer.parseInt(t[i]);
                }

                ArrayList<Day> ds = new ArrayList<Day>();
                for(int i = 0; i < d.length; i++){
                    switch(d[i]){
                    case("Monday"):
                        ds.add(Day.Monday);
                    case("Tuesday"):
                        ds.add(Day.Tuesday);
                    case("Wednesday"):
                        ds.add(Day.Wednesday);
                    case("Thursday"):
                        ds.add(Day.Thursday);
                    case("Friday"):
                        ds.add(Day.Friday);
                    case("Saturday"):
                        ds.add(Day.Saturday);
                    case("Sunday"):
                        ds.add(Day.Sunday);
                    }
                }

                Alarm alarm = new Alarm(name, hrsAndMin[0], hrsAndMin[1] , Status.ON, ds);

                addAlarm(alarm);
            }
        }
    }

    @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);
    }

    private void addAlarm(Alarm alarm){

    }
}

我花了很长时间寻找解决方案，但似乎找不到解决问题的方法。我尝试了不同的方法，但都不管用。如果有人能帮助我，我将永远感激

---

问候

虚拟机无法找到android.support.v7.app.ActionBarActivity；检查支持库jar的位置。它应该在项目的libs文件夹中才能工作

看起来所需的jar不在您的libs文件夹中。将jar复制到libs文件夹中

您需要确保在以下路径中选中了库

Go to Properties->Java Build Path->Order and Export and make sure the library is checked.

---

android-support-v4.jar在其中，但我在项目的java构建路径中添加了appcompat_v7。appcompat_v7已经包含了android-support-v4.jar。尝试从libs文件夹中删除android-support-v4.jar。此支持库的不同版本也可能导致此问题。是的，就是这样！谢谢对于其他项目，这是没有问题的，这就是为什么我找不到它。。。非常感谢@Rohit5k2Glad我能帮上忙…：

10-27 20:56:52.278: W/dalvikvm(14367): Unable to resolve superclass of Lsander/bylemans/alarm/MainActivity; (4)
10-27 20:56:52.278: W/dalvikvm(14367): Link of class 'Lsander/bylemans/alarm/MainActivity;' failed
10-27 20:56:52.298: W/dalvikvm(14367): threadid=1: thread exiting with uncaught exception (group=0x4001d560)
10-27 20:56:52.398: E/AndroidRuntime(14367): FATAL EXCEPTION: main
10-27 20:56:52.398: E/AndroidRuntime(14367): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{sander.bylemans.alarm/sander.bylemans.alarm.MainActivity}: java.lang.ClassNotFoundException: sander.bylemans.alarm.MainActivity in loader dalvik.system.PathClassLoader[/data/app/sander.bylemans.alarm-2.apk]
10-27 20:56:52.398: E/AndroidRuntime(14367):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1573)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at android.app.ActivityThread.access$1500(ActivityThread.java:117)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at android.os.Handler.dispatchMessage(Handler.java:99)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at android.os.Looper.loop(Looper.java:130)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at android.app.ActivityThread.main(ActivityThread.java:3687)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at java.lang.reflect.Method.invokeNative(Native Method)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at java.lang.reflect.Method.invoke(Method.java:507)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at dalvik.system.NativeStart.main(Native Method)
10-27 20:56:52.398: E/AndroidRuntime(14367): Caused by: java.lang.ClassNotFoundException: sander.bylemans.alarm.MainActivity in loader dalvik.system.PathClassLoader[/data/app/sander.bylemans.alarm-2.apk]
10-27 20:56:52.398: E/AndroidRuntime(14367):    at dalvik.system.PathClassLoader.findClass(PathClassLoader.java:240)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at java.lang.ClassLoader.loadClass(ClassLoader.java:551)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
10-27 20:56:52.398: E/AndroidRuntime(14367):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1565)
10-27 20:56:52.398: E/AndroidRuntime(14367):    ... 11 more

Go to Properties->Java Build Path->Order and Export and make sure the library is checked.