Android:面临Errorjava.lang.ClassCastException

Question

我想要实现的目标: 尝试将数据从我的应用程序字段发送到 WebAppServer 上的 Servlet。

我面临 ClassCastException 问题，我尝试实现我在 StackOverflow 上相关讨论中找到的建议，并做了一些更正，例如， 在“onCreate()”等中初始化我的对象

注意:我使用 Android 的 Volley 库将请求发送到 servlet。

我尝试了 .MainActivity 和 Manifest 文件中的大部分更改，但无法消除此错误。 能否请您指教。

我的“MainActivity.java”文件

package com.example.hawk;

import java.util.HashMap;
import java.util.Map;

import com.android.volley.AuthFailureError;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

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

public class MainActivity extends Activity implements View.OnClickListener {

    EditText var_sp = null;
    EditText var_ect = null;
    EditText var_er = null;
    EditText var_iat = null;
    EditText var_atp = null;
    Button submit;
    RequestQueue rq = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        var_speed = (EditText) findViewById(R.id.sp);
        var_eng_coolant_temp = (EditText) findViewById(R.id.ect);
        var_eng_rpm = (EditText) findViewById(R.id.er);
        var_in_air_temp = (EditText) findViewById(R.id.iat);
        var_abs_throttle_postn = (EditText) findViewById(R.id.atp);
        submit = (Button) findViewById(R.id.submit);        
        rq=Volley.newRequestQueue(this);
        submit.setOnClickListener(this);
    }
@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);
}

@Override
public void onClick(View v) {
    switch (v.getId()) {
    case R.id.submit:

    new Thread(new Runnable() {
    public void run() {
    try{
        StringRequest postReq = new StringRequest(Request.Method.POST, "http://192.168.0.103:8080/OBD_Feeder/post",new Response.Listener<String>() {
            protected Map<String, String> getParams() throws AuthFailureError {
                Map<String, String> params = new HashMap<String, String>();
                params.put("sp",var_speed.getText().toString());
                params.put("ect",var_eng_coolant_temp.getText().toString());
                params.put("er",var_eng_rpm.getText().toString());
                params.put("iat",var_in_air_temp.getText().toString());
                params.put("atp",var_abs_throttle_postn.getText().toString());
                return params;
            }

            @Override
            public void onResponse(String response) {
                // TODO Auto-generated method stub

            }

        }, null);

    rq.add(postReq);
    }catch(Exception e)
    {
        e.printStackTrace();
    }

    }
    }).start();

    break;


    }
    }
}

我的 Manifest.xml 文件

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

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="21" />

    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:name=".MainActivity"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".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>

我的Logcat如下

> 08-15 00:11:50.807: W/dalvikvm(9272): threadid=1: thread exiting with
> uncaught exception (group=0x41804ba8) 08-15 00:11:50.817:
> E/AndroidRuntime(9272): FATAL EXCEPTION: main 08-15 00:11:50.817:
> E/AndroidRuntime(9272): Process: com.example.hawk, PID: 9272 08-15
> 00:11:50.817: E/AndroidRuntime(9272): java.lang.RuntimeException:
> Unable to instantiate application com.example.hawk.MainActivity:
> java.lang.ClassCastException: com.example.hawk.MainActivity cannot be
> cast to android.app.Application 08-15 00:11:50.817:
> E/AndroidRuntime(9272):   at
> android.app.LoadedApk.makeApplication(LoadedApk.java:507) 08-15
> 00:11:50.817: E/AndroidRuntime(9272):     at
> android.app.ActivityThread.handleBindApplication(ActivityThread.java:4301)
> 08-15 00:11:50.817: E/AndroidRuntime(9272):   at
> android.app.ActivityThread.access$1500(ActivityThread.java:135) 08-15
> 00:11:50.817: E/AndroidRuntime(9272):     at
> android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
> 08-15 00:11:50.817: E/AndroidRuntime(9272):   at
> android.os.Handler.dispatchMessage(Handler.java:102) 08-15
> 00:11:50.817: E/AndroidRuntime(9272):     at
> android.os.Looper.loop(Looper.java:136) 08-15 00:11:50.817:
> E/AndroidRuntime(9272):   at
> android.app.ActivityThread.main(ActivityThread.java:5001) 08-15
> 00:11:50.817: E/AndroidRuntime(9272):     at
> java.lang.reflect.Method.invokeNative(Native Method) 08-15
> 00:11:50.817: E/AndroidRuntime(9272):     at
> java.lang.reflect.Method.invoke(Method.java:515) 08-15 00:11:50.817:
> E/AndroidRuntime(9272):   at
> com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
> 08-15 00:11:50.817: E/AndroidRuntime(9272):   at
> com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 08-15
> 00:11:50.817: E/AndroidRuntime(9272):     at
> dalvik.system.NativeStart.main(Native Method) 08-15 00:11:50.817:
> E/AndroidRuntime(9272): Caused by: java.lang.ClassCastException:
> com.example.hawk.MainActivity cannot be cast to
> android.app.Application 08-15 00:11:50.817: E/AndroidRuntime(9272):
>   at
> android.app.Instrumentation.newApplication(Instrumentation.java:990)
> 08-15 00:11:50.817: E/AndroidRuntime(9272):   at
> android.app.Instrumentation.newApplication(Instrumentation.java:975)
> 08-15 00:11:50.817: E/AndroidRuntime(9272):   at
> android.app.LoadedApk.makeApplication(LoadedApk.java:502) 08-15
> 00:11:50.817: E/AndroidRuntime(9272):     ... 11 more

Answer 1

这里:

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:name=".MainActivity"
    android:theme="@style/AppTheme" >

删除 android:name=".MainActivity 行。

name 属性指定 Application要使用的类。由于 MainActivity 未扩展 Application，因此您的应用会崩溃。

您实际上已经通过使用 android.intent Action 声明 intent-filter 来定义哪个 Activity 是主 Activity。操作.MAIN.