无法启动活动ComponentInfo NullpointerException-

Question

I wanted to make an app where you can make pictures and save them, but when I test it I got this error in my logcat: "java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.random/com.example.random.FotoMaker}: java.lang.NullPointerException". I think the problem has something to do with the intent, but im not sure what I need to add/change in my FotoMaker.java.

MenuScreen.java:

package com.example.random;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;
import android.widget.Button;

public class MenuScreen extends Activity {  

    @Override
    public void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);



        findViewById(R.id.test).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Log.d("DEBUG", "test");
                Intent intent = new Intent(MenuScreen.this, FotoMaker.class);
                startActivityForResult(intent, 0);
            }
        });


        findViewById(R.test1).setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {
                Log.d("DEBUG", "test1");
                Intent intent = new Intent(MenuScreen.this, FotoMaker.class);

            }
        });

        findViewById(R.test2).setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {
                Log.d("DEBUG", "test2");
                Intent intent = new Intent(MenuScreen.this, FotoMaker.class);

            }
        });



        findViewById(R.id.verlaat_app).setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {
                Log.d("DEBUG", "test3");
                MenuScreen.this.finish();
            }
        });
    }
}

MenuScreen.java:

package com.example.random;


import android.app.Activity;
import android.content.Intent;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;


public class FotoMaker extends Activity 
    {
    ImageView iv;


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

        iv = (ImageView) findViewById(R.id.imageView);
        Button btn = (Button) findViewById(R.id.testpic);
        btn.setOnClickListener(new OnClickListener()
        {
            @Override
            public void onClick (View v){
                Intent intent = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
                startActivityForResult(intent, 0);

            }
        });
        }
        @Override
        protected void onActivityResult(int requestCode, int resultCode, Intent data)
        {
            if(requestCode == 0)
            {
                Bitmap theImage = (Bitmap) data.getExtras().get("data");
                iv.setImageBitmap(theImage);
            }
        }

    }

LogCat:

11-16 18:30:14.366: E/AndroidRuntime(1522): FATAL EXCEPTION: main
11-16 18:30:14.366: E/AndroidRuntime(1522): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.random/com.example.random.FotoMaker}: java.lang.NullPointerException
11-16 18:30:14.366: E/AndroidRuntime(1522):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1996)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2023)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at android.app.ActivityThread.access$600(ActivityThread.java:127)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1174)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at android.os.Handler.dispatchMessage(Handler.java:99)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at android.os.Looper.loop(Looper.java:137)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at android.app.ActivityThread.main(ActivityThread.java:4503)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at java.lang.reflect.Method.invokeNative(Native Method)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at java.lang.reflect.Method.invoke(Method.java:511)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:809)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:576)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at dalvik.system.NativeStart.main(Native Method)
11-16 18:30:14.366: E/AndroidRuntime(1522): Caused by: java.lang.NullPointerException
11-16 18:30:14.366: E/AndroidRuntime(1522):     at com.example.random.FotoMaker.onCreate(FotoMaker.java:27)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at android.app.Activity.performCreate(Activity.java:4479)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1050)
11-16 18:30:14.366: E/AndroidRuntime(1522):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1960)
11-16 18:30:14.366: E/AndroidRuntime(1522):     ... 11 more

testpic.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:src="@drawable/ic_launcher" />

</LinearLayout>

Answer 1

It seems that you forget to add testpic button id in your xml layout,Therefore in FotoMaker activity your button btn is null.

Button btn = (Button) findViewById(R.id.testpic);  <-- null here

So add button view with id testpic in your testpic.xml layout file.

Answer 2

Button btn = (Button) findViewById(R.id.testpic);

在布局“ testpic”中没有名为testpic的 Button，您需要添加一个testtest ind您的布局文件，否则它将返回null。