应用程序在按钮单击时崩溃，说尝试调用虚拟方法'void android.widget.Button.setOnClickListener'

Question

当我点击activity_home.xml的Upload Photo按钮时，这个代码给了我错误。这个应用程序工作得很好，直到我没有添加上传活动。上传活动是关于将图片推送到ftp服务器。上传活动工作良好作为一个独立的apk。这个错误显示当我加入这两个独立的apks与创建一个意图b/w两个单独的视图。

我不确定应用程序崩溃的按钮点击。

<<p> 日志异常/strong>

Process: com.muchmore.www.chasquido, PID: 9571
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.muchmore.www.chasquido/com.muchmore.www.chasquido.Upload}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2372)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2434)
            at android.app.ActivityThread.access$800(ActivityThread.java:162)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5424)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:913)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:706)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
            at com.muchmore.www.chasquido.Upload.onCreate(Upload.java:30)
            at android.app.Activity.performCreate(Activity.java:6093)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2434)
            at android.app.ActivityThread.access$800(ActivityThread.java:162)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5424)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:913)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:706)

Home.java

package com.muchmore.www.chasquido;
import android.graphics.Typeface;
import android.media.MediaPlayer;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.ImageView;
import android.content.pm.PackageInfo;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.provider.MediaStore;
import android.widget.ImageButton;
import android.view.View;
// new imports
import android.graphics.Color;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.RelativeLayout;
import android.app.AlertDialog;
import android.app.Service;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.os.IBinder;
import android.provider.Settings;
import android.util.Log;
import android.widget.Toast;

public class Home extends AppCompatActivity {
    static final int REQUEST_IMAGE_CAPTURE = 1;
    ImageView imageView;
    Button btnShowLocation;
    GPSTracker gps;

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

        //          Media Player
        Runnable backgroundSound = new Runnable() {
            @Override
            public void run() {
                MediaPlayer mediaPlayer1= MediaPlayer.create(Home.this, R.raw.welcome_message);
                mediaPlayer1.start();
                MediaPlayer mediaPlayer2= MediaPlayer.create(Home.this, R.raw.welcome_tone);
                mediaPlayer2.start();
            }
        };
        Thread media = new Thread(backgroundSound);
        media.start();
        //          Media Player
        //          Font
        final TextView userMessage = (TextView) findViewById(R.id.welcome_tag);
        Typeface customWelcomeMessage = (Typeface)Typeface.createFromAsset(getAssets(), "PoiretOne-Regular.ttf");
        userMessage.setTypeface(customWelcomeMessage);
        //          Font
        //          Intent Import and show top Text
        Bundle achieve = getIntent().getExtras();
        Boolean anonymousUser = false;
        if(achieve == null){
            anonymousUser = true;
            return;
        }
        String userName= achieve.getString("Username");
        if(anonymousUser == false) {
            userMessage.setText("Welcome " + userName + ", You can now take a snap, edit it and upload it to the Server.");
        }
        if(anonymousUser == true){
            userMessage.setText("Welcome Annoymous User, You can't do anything here. Buzz off!!");
        }
        //          Intent Import and show top Text
        // GPS
        Runnable r = new Runnable() {
            @Override
            public void run() {
                btnShowLocation = (Button)findViewById(R.id.show_location);
                btnShowLocation.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        gps = new GPSTracker(Home.this);
                        if(gps.canGetLocation()) {
                            double latitude = gps.getLatitude();
                            double longitude = gps.getLongitude();
                            Toast.makeText(
                                    getApplicationContext(),
                                    "Your Location is -nLat: " + latitude + "nLong: "
                                            + longitude, Toast.LENGTH_LONG).show();
                        } else {
                            gps.showSettingsAlert();
                        }
                    }
                });
            }
        };

        Thread th = new Thread(r);
        th.start();
        // GPS
        //          CAMERA BUTTON IMPLEMENTATION
        ImageButton cameraButton = (ImageButton)findViewById(R.id.imageButton);
        imageView = (ImageView)findViewById(R.id.imageView);
                    /* Disable the button if the user doesn't have camera */
        if(!hasCamera())
            cameraButton.setEnabled(false);
        //          CAMERA BUTTON IMPLEMENTATION

    }

    // Upload View Load
    public void loadUpload(View view){
        Log.d("MyMessage", "On Upload Button Click");
        Intent intent = new Intent(Home.this, Upload.class);
        startActivity(intent);
        Log.d("MyMessage", "Starting Intent");
    }
    //

    // Check if the user has a camera
    private boolean hasCamera(){
        return getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA_ANY);
    }
    // Launching the camera
    public void launchCamera(View view){
        Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        //Take a picture and pass results along to onActivityResult
        startActivityForResult(intent, REQUEST_IMAGE_CAPTURE);
    }

    // If you want to return the image taken
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data){
        if(requestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK){
            //Get the photo
            Bundle extras = data.getExtras();
            Bitmap photo = (Bitmap) extras.get("data");
            imageView.setImageBitmap(photo);
        }
    }

activity_home.xml

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:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context="com.muchmore.www.chasquido.Home"
    android:background="@drawable/home_background"
    android:id="@+id/home_activity"
    >
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Welcome User!!!"
        android:id="@+id/welcome_tag"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:textColor="#000"
        />
    <ImageButton
        android:layout_width="90dp"
        android:layout_height="90dp"
        android:id="@+id/imageButton"
        android:background="@drawable/camera_button"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:onClick="launchCamera"
        />
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/imageView"
        android:minHeight="300dp"
        android:minWidth="300dp"
        android:layout_above="@+id/imageButton"
        android:layout_centerHorizontal="true" />
    <Button
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Location"
        android:id="@+id/show_location"
        android:layout_above="@+id/imageView"
        android:layout_toRightOf="@+id/imageButton"
        android:layout_toEndOf="@+id/imageButton" />
    <Button
        style="?android:attr/buttonStyleSmall"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Upload Photo"
        android:id="@+id/upload"
        android:layout_above="@+id/imageView"
        android:layout_alignLeft="@+id/imageView"
        android:layout_alignStart="@+id/imageView"
        android:onClick="loadUpload" />
</RelativeLayout>

Upload.java

package com.muchmore.www.chasquido;
import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class Upload extends Activity {
    private static final int MY_INTENT_CLICK=302;
    private TextView txta;
    private Button btn_selectImage;
    String myGlobalImagePath = "";
    Runnable r;
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        txta = (TextView) findViewById(R.id.textView1);
        btn_selectImage = (Button) findViewById(R.id.btn_selectImage);
        btn_selectImage.setOnClickListener(new OnClickListener()
        {
            @Override
            public void onClick(View v)
            {
                Intent intent = new Intent();
                intent.setType("*/*");
                intent.setAction(Intent.ACTION_GET_CONTENT);
                startActivityForResult(Intent.createChooser(intent, "Select File"),MY_INTENT_CLICK);
            }
        });
        r = new Runnable() {
            @Override
            public void run() {
                Ftp obj = new Ftp();
                obj.ftpConnect("cp.mdurtk.in", "cp.mdurtk.in|cp", "cp@123", 21);
                //obj.ftpUpload(myGlobalImagePath,"file.jpg", "/vikas");
                obj.ftpMyUpload(myGlobalImagePath);
            }
        };
    }
    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data)
    {
        if (resultCode == RESULT_OK)
        {
            if (requestCode == MY_INTENT_CLICK)
            {
                if (null == data) return;
                String selectedImagePath;
                Uri selectedImageUri = data.getData();
                //MEDIA GALLERY
                selectedImagePath = ImageFilePath.getPath(getApplicationContext(), selectedImageUri);
                myGlobalImagePath = selectedImagePath;
                Log.i("Image File Path", ""+selectedImagePath);
                txta.setText("File Path : n"+selectedImagePath);           }
        }
        Thread t = new Thread(r);
        t.start();
    }
}

activity_upload.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="30dp" >
    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Howdy Buddy! Select an image from your device and the image will be automatically uploaded to the server. You need not to do anything. Isn't that cool? Well yaa cool app for cool buddies."
        android:textSize="14sp"
        android:textStyle="bold" />
    <Button
        android:id="@+id/btn_selectImage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="10dp"
        android:layout_marginTop="10dp"
        android:text="Select Image" />
    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:textSize="14sp"
        android:textStyle="bold" />
</LinearLayout>

Answer 1

您将layout.xml设置为上传活动的View内容。

你应该做

setContentView(R.layout.activity_upload);

而不是做

setContentView(R.layout.activity_main);

Answer 2

您正在尝试调用Upload.java上的null对象的方法，30行