NulPointerException，Android应用程序意外关闭

Question

有谁能告诉我为什么我的申请意外关闭了？

以下是LogCat错误，但我不知道它们的含义，需要帮助。

LogCat错误

10-08 11:15:00.556: E/AndroidRuntime(275): FATAL EXCEPTION: main
10-08 11:15:00.556: E/AndroidRuntime(275): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.fyp.atms/com.fyp.atms.MainActivity}: java.lang.NullPointerException
10-08 11:15:00.556: E/AndroidRuntime(275):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
10-08 11:15:00.556: E/AndroidRuntime(275):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
10-08 11:15:00.556: E/AndroidRuntime(275):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
10-08 11:15:00.556: E/AndroidRuntime(275):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
10-08 11:15:00.556: E/AndroidRuntime(275):  at android.os.Handler.dispatchMessage(Handler.java:99)
10-08 11:15:00.556: E/AndroidRuntime(275):  at android.os.Looper.loop(Looper.java:123)
10-08 11:15:00.556: E/AndroidRuntime(275):  at android.app.ActivityThread.main(ActivityThread.java:4627)
10-08 11:15:00.556: E/AndroidRuntime(275):  at java.lang.reflect.Method.invokeNative(Native Method)
10-08 11:15:00.556: E/AndroidRuntime(275):  at java.lang.reflect.Method.invoke(Method.java:521)
10-08 11:15:00.556: E/AndroidRuntime(275):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
10-08 11:15:00.556: E/AndroidRuntime(275):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
10-08 11:15:00.556: E/AndroidRuntime(275):  at dalvik.system.NativeStart.main(Native Method)
10-08 11:15:00.556: E/AndroidRuntime(275): Caused by: java.lang.NullPointerException
10-08 11:15:00.556: E/AndroidRuntime(275):  at com.fyp.atms.MainActivity.onCreate(MainActivity.java:30)
10-08 11:15:00.556: E/AndroidRuntime(275):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-08 11:15:00.556: E/AndroidRuntime(275):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
10-08 11:15:00.556: E/AndroidRuntime(275):  ... 11 more

MainActivity.java

package com.fyp.atms;

import android.support.v7.app.ActionBarActivity;
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;
import android.widget.TextView;

import com.memetix.mst.language.Language;
import com.memetix.mst.translate.Translate;

public class MainActivity extends ActionBarActivity implements OnClickListener{

    TextView tled;
    EditText toTl;
    Button translate;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Translate.setClientId("bharatnakka");
        Translate.setClientSecret("+HLa1sMAlW6Kw6XpNcIo+m2DxLZySLpmV2BgT96sA2s=");

        translate.setOnClickListener(this);

        translate = (Button) findViewById(R.id.btnT);   // translate button
        tled = (TextView) findViewById(R.id.Ted);   // translated
        toTl = (EditText) findViewById(R.id.toT);   // to be translate

        translate.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                switch(v.getId()){
                case R.id.btnT:
                    String input = toTl.getText().toString();
                    try {
                        String output = Translate.execute(input, Language.AUTO_DETECT, Language.FRENCH);

                    toTl.setText(input);
                    tled.setText(output);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }


            }
        });
    }

    @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) {
        // TODO Auto-generated method stub

    }
}

activity_main.xml中

<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="com.fyp.atms.MainActivity" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_marginTop="28dp"
        android:text="@string/atms"
        android:gravity="center"
        android:textSize="20dp" />

    <EditText
        android:id="@+id/toT"
        android:hint="Type to translate..."
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/textView1"
        android:layout_below="@+id/textView1"
        android:layout_marginTop="40dp"
        android:ems="10" />

    <Button
        android:id="@+id/btnT"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="Translate" />

    <TextView
        android:id="@+id/Ted"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/toT"
        android:layout_below="@+id/btnT"
        android:layout_marginTop="57dp"
        android:textAppearance="?android:attr/textAppearanceLarge" />

</RelativeLayout>

atms Manifest

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

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

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

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Answer 1

从

更改此订单

 translate.setOnClickListener(this);
 translate = (Button) findViewById(R.id.btnT); 

到

 translate = (Button) findViewById(R.id.btnT); 
 translate.setOnClickListener(this);

您应首先初始化translate Button，然后将OnClickListner()设置为Button

Answer 2

translate按钮从未初始化。

事实上，它已初始化但为时已晚，在对此对象执行任何其他操作之前先执行translate = (Button) findViewById(R.id.btnT);。

Answer 3

修改您的课程，如下所示！

---

<强> MainActivity.java

package com.fyp.atms;

import android.support.v7.app.ActionBarActivity;
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;
import android.widget.TextView;

import com.memetix.mst.language.Language;
import com.memetix.mst.translate.Translate;

public class MainActivity extends ActionBarActivity implements OnClickListener{

    TextView tled;
    EditText toTl;
    Button translate;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Translate.setClientId("bharatnakka");
        Translate.setClientSecret("+HLa1sMAlW6Kw6XpNcIo+m2DxLZySLpmV2BgT96sA2s=");

        translate = (Button) findViewById(R.id.btnT);   // translate button
        tled = (TextView) findViewById(R.id.Ted);   // translated
        toTl = (EditText) findViewById(R.id.toT);   // to be translate

        translate.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                switch(v.getId()){
                case R.id.btnT:
                    String input = toTl.getText().toString();
                    try {
                        String output = Translate.execute(input, Language.AUTO_DETECT, Language.FRENCH);

                    toTl.setText(input);
                    tled.setText(output);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }


            }
        });
    }

    @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) {
        // TODO Auto-generated method stub

    }
}