使用设备管理员时应用中的Android实例化异常

Question

I am getting there!

Logcat:

07-29 19:15:05.509: D/libEGL(31021): loaded /system/lib/egl/libEGL_mali.so
07-29 19:15:05.544: D/libEGL(31021): loaded /system/lib/egl/libGLESv1_CM_mali.so
07-29 19:15:05.549: D/libEGL(31021): loaded /system/lib/egl/libGLESv2_mali.so
07-29 19:15:05.549: D/(31021): Device driver API match
07-29 19:15:05.549: D/(31021): Device driver API version: 10
07-29 19:15:05.549: D/(31021): User space API version: 10 
07-29 19:15:05.549: D/(31021): mali: REVISION=Linux-r2p4-02rel0 BUILD_DATE=Mon Mar  5 09:47:55 KST 2012 
07-29 19:15:05.574: D/OpenGLRenderer(31021): Enabling debug mode 0
07-29 19:15:07.509: W/IInputConnectionWrapper(31021): showStatusIcon on inactive InputConnection
07-29 19:15:08.444: D/dalvikvm(31021): newInstance failed: no <init>()
07-29 19:15:08.444: D/AndroidRuntime(31021): Shutting down VM
07-29 19:15:08.444: W/dalvikvm(31021): threadid=1: thread exiting with uncaught exception (group=0x41443300)
07-29 19:15:08.549: E/AndroidRuntime(31021): FATAL EXCEPTION: main
07-29 19:15:08.549: E/AndroidRuntime(31021): java.lang.RuntimeException: Unable to instantiate receiver com.liamwli.parent.trap.ParentTrap$Controller: java.lang.InstantiationException: can't instantiate class com.liamwli.parent.trap.ParentTrap$Controller; no empty constructor
07-29 19:15:08.549: E/AndroidRuntime(31021):    at android.app.ActivityThread.handleReceiver(ActivityThread.java:2333)
07-29 19:15:08.549: E/AndroidRuntime(31021):    at android.app.ActivityThread.access$1500(ActivityThread.java:139)
07-29 19:15:08.549: E/AndroidRuntime(31021):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1281)
07-29 19:15:08.549: E/AndroidRuntime(31021):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-29 19:15:08.549: E/AndroidRuntime(31021):    at android.os.Looper.loop(Looper.java:137)
07-29 19:15:08.549: E/AndroidRuntime(31021):    at android.app.ActivityThread.main(ActivityThread.java:4896)
07-29 19:15:08.549: E/AndroidRuntime(31021):    at java.lang.reflect.Method.invokeNative(Native Method)
07-29 19:15:08.549: E/AndroidRuntime(31021):    at java.lang.reflect.Method.invoke(Method.java:511)
07-29 19:15:08.549: E/AndroidRuntime(31021):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:788)
07-29 19:15:08.549: E/AndroidRuntime(31021):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
07-29 19:15:08.549: E/AndroidRuntime(31021):    at dalvik.system.NativeStart.main(Native Method)
07-29 19:15:08.549: E/AndroidRuntime(31021): Caused by: java.lang.InstantiationException: can't instantiate class com.liamwli.parent.trap.ParentTrap$Controller; no empty constructor
07-29 19:15:08.549: E/AndroidRuntime(31021):    at java.lang.Class.newInstanceImpl(Native Method)
07-29 19:15:08.549: E/AndroidRuntime(31021):    at java.lang.Class.newInstance(Class.java:1319)
07-29 19:15:08.549: E/AndroidRuntime(31021):    at android.app.ActivityThread.handleReceiver(ActivityThread.java:2328)
07-29 19:15:08.549: E/AndroidRuntime(31021):    ... 10 more
07-29 19:15:09.719: I/Process(31021): Sending signal. PID: 31021 SIG: 9

Acitvity:

package com.liamwli.parent.trap;

import android.os.Bundle;
import android.app.Activity;
import android.app.admin.DeviceAdminReceiver;
import android.app.admin.DevicePolicyManager;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import android.support.v4.app.NavUtils;



public class ParentTrap extends Activity {

    Button dae, dad, spass;
    EditText pass;
    ComponentName mDeviceAdminSample;
    static final int RESULT_ENABLE = 1;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        dae = (Button) findViewById(R.id.benablea);
        dae.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub

                mDeviceAdminSample = new ComponentName(ParentTrap.this,
                        Controller.class);

                Intent intent = new Intent(
                        DevicePolicyManager.ACTION_ADD_DEVICE_ADMIN);
                intent.putExtra(DevicePolicyManager.EXTRA_DEVICE_ADMIN,
                        mDeviceAdminSample);
                intent.putExtra(DevicePolicyManager.EXTRA_ADD_EXPLANATION,
                        "Title");
                startActivityForResult(intent, RESULT_ENABLE);

            }
        });
        dad = (Button) findViewById(R.id.button1);
        dad.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub

            }
        });
        spass = (Button) findViewById(R.id.button2);
        spass.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub

            }
        });

        pass = (EditText) findViewById(R.id.editText1);

        dad.setEnabled(false);
    }

    public class Controller extends DeviceAdminReceiver {

        void showToast(Context context, String msg) {
            String status = "Status";
            Toast.makeText(context, status, Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onEnabled(Context context, Intent intent) {
            showToast(context, "Enabled");
        }

        @Override
        public CharSequence onDisableRequested(Context context, Intent intent) {
            return "Disable Requested";
        }

        @Override
        public void onDisabled(Context context, Intent intent) {
            showToast(context, "Disabled");
        }

        @Override
        public void onPasswordChanged(Context context, Intent intent) {
            showToast(context, "Device PIN Changed");
        }

    }

}

class evilliam {

}
// @Override
// public boolean onCreateOptionsMenu(Menu menu) {
// getMenuInflater().inflate(R.menu.main, menu);
// return true;
// }

Please help me with this question, and I promise not to bother you until tomorrow :)

Answer 1

Caused by: java.lang.InstantiationException: can't instantiate class com.liamwli.parent.trap.ParentTrap$Controller; no empty constructor

This suggests that Controller needs a default constructor, like this:

public class Controller extends DeviceAdminReceiver {
    public Controller() {
        super();
    }

    void showToast(Context context, String msg) {
        String status = "Status";
        Toast.makeText(context, status, Toast.LENGTH_SHORT).show();

        //Toast.makeText(context, msg, Toast.LENGTH_SHORT).show();
    }
    ...
}