新活动不是从Eclipse开始的

Question

我已经链接了许多活动，以构建一个应用程序，但是最初的一个，现在当我开始时，在使用时会出错。尽管该活动最初工作，但现在，它显示应用程序已强制关闭。任何人都可以帮我解决这个问题吗？另外，如何附加logcat，请告诉我。我希望看到这可能会帮助你们所有人，更好地解决问题。 谢谢！

package com.example.newapplication;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;


public class MainActivity extends Activity {

    int counter;
    Button add, sub, change, mail, camera;
    TextView display;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_main);

       add = (Button) findViewById(R.id.add);
       sub = (Button) findViewById(R.id.sub);
       display=(TextView) findViewById(R.id.textView1);
       change = (Button) findViewById(R.id.change);
       mail = (Button) findViewById(R.id.mail);
       camera = (Button) findViewById(R.id.camera);

       add.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            counter = counter + 1;
            display.setText("Answer is "+ counter);

        }
    });

       sub.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            counter = counter - 1;
            display.setText("Answer is "+ counter);

        }
    });

      change.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            Intent startTextPlay = new Intent("com.example.newapplication.TEXTPLAY");
            startActivity(startTextPlay);
        }
    });

      mail.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            Intent startMailer = new Intent("com.example.newapplication.EMAIL");
            startActivity(startMailer);

        }
    });

      camera.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            Intent startCamera = new Intent("com.example.newapplication.CAMERA");
            startActivity(startCamera);

        }
    });

    }
}

这是主要活动中的代码，活动的代码没有启动，下面再次给出了更改。

package com.example.newapplication;

import java.util.Random;

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.text.InputType;
import android.view.Gravity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.ToggleButton;

public class TextPlay extends Activity{

    Button chkCommand = (Button) findViewById(R.id.b1);
    ToggleButton passTog = (ToggleButton) findViewById(R.id.tB1);
    EditText input = (EditText) findViewById(R.id.etCommands);
    TextView display = (TextView) findViewById(R.id.tv);

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

        passTog.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                if (passTog.isChecked()){
                    input.setInputType(InputType.TYPE_CLASS_TEXT | InputType.TYPE_TEXT_VARIATION_PASSWORD);
                } else{
                    input.setInputType(InputType.TYPE_CLASS_TEXT);
                }
            }
        });

        chkCommand.setOnClickListener(new View.OnClickListener() {          
            @Override
            public void onClick(View arg0) {
                String message = input.getText().toString();
                if(message.contentEquals("naman")){
                    display.setTextColor(Color.GREEN);
                    display.setGravity(Gravity.CENTER);
                    display.setText("Password is correct");
                    Random crazy = new Random();
                    display.setTextSize(crazy.nextInt(75));
                    display.setTextColor(Color.rgb(crazy.nextInt(200), crazy.nextInt(256), crazy.nextInt(256)));
                }
                else{
                    display.setTextColor(Color.RED);
                    display.setGravity(Gravity.CENTER);
                    display.setText("Invalid Password");
                }
            }
        });
    }



}

logcat如下所示：

05-29 01:52:40.280: E/AndroidRuntime(892): FATAL EXCEPTION: main
05-29 01:52:40.280: E/AndroidRuntime(892): Process: com.example.newapplication, PID: 892
05-29 01:52:40.280: E/AndroidRuntime(892): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.newapplication/com.example.newapplication.TextPlay}: java.lang.NullPointerException
05-29 01:52:40.280: E/AndroidRuntime(892):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
05-29 01:52:40.280: E/AndroidRuntime(892):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
05-29 01:52:40.280: E/AndroidRuntime(892):  at android.app.ActivityThread.access$800(ActivityThread.java:135)
05-29 01:52:40.280: E/AndroidRuntime(892):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
05-29 01:52:40.280: E/AndroidRuntime(892):  at android.os.Handler.dispatchMessage(Handler.java:102)
05-29 01:52:40.280: E/AndroidRuntime(892):  at android.os.Looper.loop(Looper.java:136)
05-29 01:52:40.280: E/AndroidRuntime(892):  at android.app.ActivityThread.main(ActivityThread.java:5017)
05-29 01:52:40.280: E/AndroidRuntime(892):  at java.lang.reflect.Method.invokeNative(Native Method)
05-29 01:52:40.280: E/AndroidRuntime(892):  at java.lang.reflect.Method.invoke(Method.java:515)
05-29 01:52:40.280: E/AndroidRuntime(892):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
05-29 01:52:40.280: E/AndroidRuntime(892):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
05-29 01:52:40.280: E/AndroidRuntime(892):  at dalvik.system.NativeStart.main(Native Method)
05-29 01:52:40.280: E/AndroidRuntime(892): Caused by: java.lang.NullPointerException
05-29 01:52:40.280: E/AndroidRuntime(892):  at android.app.Activity.findViewById(Activity.java:1884)
05-29 01:52:40.280: E/AndroidRuntime(892):  at com.example.newapplication.TextPlay.<init>(TextPlay.java:18)
05-29 01:52:40.280: E/AndroidRuntime(892):  at java.lang.Class.newInstanceImpl(Native Method)
05-29 01:52:40.280: E/AndroidRuntime(892):  at java.lang.Class.newInstance(Class.java:1208)
05-29 01:52:40.280: E/AndroidRuntime(892):  at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
05-29 01:52:40.280: E/AndroidRuntime(892):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
05-29 01:52:40.280: E/AndroidRuntime(892):  ... 11 more

Android Manifest文件如下：

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

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="19" />
    <permission android:name="android.permission.SET_WALLPAPER"></permission>

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.newapplication.Splash"
            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="com.example.newapplication.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="com.example.newapplication.MAINACTIVITY" />

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

        <activity
            android:name="com.example.newapplication.TextPlay"
            android:label="@string/app_name" 
            android:screenOrientation="portrait"
            >
            <intent-filter>
                <action android:name="com.example.newapplication.TEXTPLAY" />

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

        <activity
            android:name="com.example.newapplication.Email"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="com.example.newapplication.EMAIL" />

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

        <activity
            android:name="com.example.newapplication.Camera"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="com.example.newapplication.CAMERA" />

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


    </application>

</manifest>

Answer 1

移动此代码TextPlay.java

Button chkCommand = (Button) findViewById(R.id.b1);
ToggleButton passTog = (ToggleButton) findViewById(R.id.tB1);
EditText input = (EditText) findViewById(R.id.etCommands);
TextView display = (TextView) findViewById(R.id.tv);

之后

setContentView(R.layout.text);

在设置xml文件的内容之前尝试查找视图时，您将收到Null Pointer Exception。希望这会有所帮助。

Answer 2

此代码：

Button chkCommand = (Button) findViewById(R.id.b1);
ToggleButton passTog = (ToggleButton) findViewById(R.id.tB1);
EditText input = (EditText) findViewById(R.id.etCommands);
TextView display = (TextView) findViewById(R.id.tv);

它应该在OnCreate方法内部并且在setContentView(R.layout.text);下面这一行在类中你可以声明变量初始化在OnCreate方法中完成。

public class TextPlay extends Activity{

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

        Button chkCommand = (Button) findViewById(R.id.b1);
        ToggleButton passTog = (ToggleButton) findViewById(R.id.tB1);
        EditText input = (EditText) findViewById(R.id.etCommands);
        TextView display = (TextView) findViewById(R.id.tv);


        passTog.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                if (passTog.isChecked()){
                    input.setInputType(InputType.TYPE_CLASS_TEXT | InputType.TYPE_TEXT_VARIATION_PASSWORD);
                } else{
                    input.setInputType(InputType.TYPE_CLASS_TEXT);
                }
            }
        });

        chkCommand.setOnClickListener(new View.OnClickListener() {          
            @Override
            public void onClick(View arg0) {
                String message = input.getText().toString();
                if(message.contentEquals("naman")){
                    display.setTextColor(Color.GREEN);
                    display.setGravity(Gravity.CENTER);
                    display.setText("Password is correct");
                    Random crazy = new Random();
                    display.setTextSize(crazy.nextInt(75));
                    display.setTextColor(Color.rgb(crazy.nextInt(200), crazy.nextInt(256), crazy.nextInt(256)));
                }
                else{
                    display.setTextColor(Color.RED);
                    display.setGravity(Gravity.CENTER);
                    display.setText("Invalid Password");
                }
            }
        });
    }



}