我有一个 Android 应用程序。这个应用程序有 12 个活动，第一个活动是启动屏幕，第二个活动是 intropage，第三个活动是主要等等当我运行应用程序时，它不会进入主活动并且应用程序关闭。错误如下：
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplication/com.example.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setAlpha(float)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setAlpha(float)' on a null object reference
at com.github.hujiaweibujidao.wava.BaseViewAnimator.reset(BaseViewAnimator.java:78)
at com.github.hujiaweibujidao.wava.BaseViewAnimator.start(BaseViewAnimator.java:55)
at com.github.hujiaweibujidao.wava.YoYo$Builder.start(YoYo.java:128)
at com.github.hujiaweibujidao.wava.YoYo$Builder.playOn(YoYo.java:115)
at com.example.myapplication.MainActivity.onCreate(MainActivity.java:108)
at android.app.Activity.performCreate(Activity.java:6679)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
感谢您的回答，但是您给我的解决方案没有帮助。我检查了，但它仍然给了我同样的错误。我给你放了三激活码。你能帮我吗？
这是我的主要活动java代码：
package com.example.myapplication;
import android.Manifest;
import android.annotation.SuppressLint;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.SharedPreferences;
import android.graphics.Color;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.provider.Settings;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import android.util.Log;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;
import com.akshay.library.CurveBottomBar;
import com.github.hujiaweibujidao.wava.Techniques;
import com.github.hujiaweibujidao.wava.YoYo;
import com.google.android.material.bottomnavigation.BottomNavigationView;
import com.karumi.dexter.Dexter;
import com.karumi.dexter.PermissionToken;
import com.karumi.dexter.listener.PermissionDeniedResponse;
import com.karumi.dexter.listener.PermissionGrantedResponse;
import com.karumi.dexter.listener.PermissionRequest;
import com.karumi.dexter.listener.single.PermissionListener;
import com.mxn.soul.flowingdrawer_core.ElasticDrawer;
import com.mxn.soul.flowingdrawer_core.FlowingDrawer;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import uk.co.samuelwall.materialtaptargetprompt.MaterialTapTargetPrompt;
public class MainActivity extends AppCompatActivity {
CurveBottomBar cbb;
FlowingDrawer mDrawer;
ImageView img_icon,imgtest,img_music,img_night,img_main,img_setting;
TextView txt;
String patch;
boolean read=false,music=true,night_mode;
Button btn_fehrest,btn_last_story,btn_fav;
SharedPreferences sharedP;
LinearLayout lin_main;
Toast exit;
boolean show_intropage;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
cbb = findViewById(R.id.cbb);
mDrawer = findViewById(R.id.drawerlayout);
img_icon = findViewById(R.id.img_icon);
imgtest = findViewById(R.id.imgtest);
txt = findViewById(R.id.txt);
btn_fehrest = findViewById(R.id.btn_fehrest);
img_music = findViewById(R.id.img_music);
lin_main = findViewById(R.id.lin_main);
img_night = findViewById(R.id.img_night);
img_main = findViewById(R.id.img_main);
btn_last_story = findViewById(R.id.btn_last_story);
btn_fav = findViewById(R.id.btn_fav);
img_setting = findViewById(R.id.img_setting);
cbb.inflateMenu(R.menu.menu_scrolling);
sharedP = getSharedPreferences(Items.SETTINGS, Context.MODE_PRIVATE);
show_intropage = sharedP.getBoolean(Items.INTROPAGE,true);
cbb.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
switch (menuItem.getItemId()){
case R.id.img_setting:
// kary ke mikhaym anjam bedim
break;
case R.id.img_music:
//
break;
}
return false;
}
});
YoYo.with(Techniques.ZoomInDown).duration(1000).playOn(btn_fehrest);
YoYo.with(Techniques.ZoomInDown).duration(1000).playOn(btn_last_story);
YoYo.with(Techniques.ZoomInDown).duration(1000).playOn(btn_fav);
YoYo.with(Techniques.ZoomInDown).duration(1000).playOn(img_music);
YoYo.with(Techniques.ZoomInDown).duration(1000).playOn(img_setting);
get_night();
permission();
//createFile();
if (show_intropage){
taptarget();
}
img_icon.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mDrawer.openMenu(true);
}
});
mDrawer.setTouchMode(ElasticDrawer.TOUCH_MODE_BEZEL);
mDrawer.setBackgroundColor(Color.WHITE);
mDrawer.setOnDrawerStateChangeListener(new ElasticDrawer.OnDrawerStateChangeListener() {
@Override
public void onDrawerStateChange(int oldState, int newState) {
if (newState == ElasticDrawer.STATE_CLOSED) {
Log.i("MainActivity", "Drawer STATE_CLOSED");
}
}
@Override
public void onDrawerSlide(float openRatio, int offsetPixels) {
Log.i("MainActivity", "openRatio=" + openRatio + " ,offsetPixels=" + offsetPixels);
}
});
}
public void createFile(){
try {
patch = Environment.getExternalStorageDirectory().getAbsolutePath() + "/Mbook/";
File mfile = new File(patch);
if (!mfile.exists()) {
mfile.mkdir();
mfile.createNewFile();
CopyDB(getBaseContext().getAssets().open("Mbook.db"), new FileOutputStream(patch+"/Mbook.db"));
//Toast.makeText(this, patch+"", Toast.LENGTH_LONG).show();
}
}catch (FileNotFoundException e){
e.printStackTrace();
}catch (IOException e){
e.printStackTrace();
}
}
public void CopyDB (InputStream inputStream, OutputStream outputStream) throws IOException {
byte[] buffer = new byte[1024];
int file_length;
while ((file_length = inputStream.read(buffer))>0){
outputStream.write(buffer,0,file_length);
}
inputStream.close();
outputStream.close();
}
public void fehrest_intent(View view) {
mDrawer.closeMenu(true);
YoYo.with(Techniques.Pulse).duration(800).playOn(btn_fehrest);
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
Intent intent = new Intent(getBaseContext(), Fehrest.class);
intent.putExtra("button","fehrest");
startActivity(intent);
}
},1500);
}
private void permission(){
Dexter.withContext(MainActivity.this)
.withPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE)
.withListener(new PermissionListener() {
@Override
public void onPermissionGranted(PermissionGrantedResponse response) {
createFile();
}
@Override
public void onPermissionDenied(PermissionDeniedResponse response) {
if (response !=null && response.isPermanentlyDenied()){
AlertDialog.Builder Hoshdar = new AlertDialog.Builder(MainActivity.this);
Hoshdar.setMessage("جهت استفاده از برنامه دادن اجازه دسترسی ضروریست");
Hoshdar.setCancelable(false);
Hoshdar.setPositiveButton("رفتن به تنظیمات", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
Intent intent = new Intent(Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
intent.setData(Uri.fromParts("package",getPackageName(),null));
startActivity(intent);
}
});
}
Toast.makeText(MainActivity.this, "جهت استفاده از برنامه دادن اجازه دسترسی ضروریست", Toast.LENGTH_SHORT).show();
alert();
}
@Override
public void onPermissionRationaleShouldBeShown(PermissionRequest permission, final PermissionToken token) {
alert();
}
}).check();
}
public void alert(){
AlertDialog.Builder Hoshdar = new AlertDialog.Builder(MainActivity.this);
Hoshdar.setTitle("توجه");
Hoshdar.setMessage("جهت استفاده از برنامه دادن اجازه دسترسی ضروریست لطفا درقسمت تنظیمات اجازه دسترسی را فعال کنید");
Hoshdar.setCancelable(false);
Hoshdar.setPositiveButton("رفتن به تنظیمات", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
Intent intent = new Intent(Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
intent.setData(Uri.fromParts("package",getPackageName(),null));
startActivity(intent);
}
});
Hoshdar.create().show();
}
public void fav_intent(View view) {
YoYo.with(Techniques.Pulse).duration(600).playOn(btn_fav);
mDrawer.closeMenu(true);
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
Intent intent = new Intent(getBaseContext(), Fehrest.class);
intent.putExtra("button","fav");
intent.putExtra("activity","main");
startActivity(intent);
}
},1500);
}
public void text_intent(View view) {
YoYo.with(Techniques.Pulse).duration(600).playOn(btn_last_story);
if (read){
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
Intent intent_movies = new Intent(getBaseContext(), Text_activity.class);
intent_movies.putExtra("activity","main");
startActivity(intent_movies);
}
},1500);
}else {
Toast.makeText(this, "هنوز هیچ داستانی مطالعه نکردید!", Toast.LENGTH_SHORT).show();
}
}
public void setting_intent(MenuItem item) {
mDrawer.closeMenu(true);
YoYo.with(Techniques.Pulse).duration(600).playOn(img_setting);
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
startActivity(new Intent(MainActivity.this,Setting.class));
}
},1500);
}
public void set_music(MenuItem item) {
YoYo.with(Techniques.Pulse).duration(600).playOn(img_music);
if (music){
stopService(new Intent(MainActivity.this,PlayMusic.class));
img_music.setBackgroundResource(R.drawable.music_off_icon);
music=false;
sharedP.edit().putBoolean(Items.MUSIC, false).apply();
}else {
startService(new Intent(MainActivity.this,PlayMusic.class));
img_music.setBackgroundResource(R.drawable.music_on_icon);
music=true;
sharedP.edit().putBoolean(Items.MUSIC, true).apply();
}
}
public void get_night(){
music = sharedP.getBoolean(Items.MUSIC,true);
night_mode = sharedP.getBoolean(Items.NIGHT_MODE,false);
read = sharedP.getBoolean(Items.READ,false);
if (night_mode){
lin_main.setBackgroundResource(R.color.Black0);
img_night.setBackgroundResource(R.drawable.sun_icon);
img_main.setBackgroundResource(R.drawable.main2);
}else {
lin_main.setBackgroundResource(0);
img_night.setBackgroundResource(R.drawable.moon_icon);
img_main.setBackgroundResource(R.drawable.main);
}
if (!music){
stopService(new Intent(MainActivity.this,PlayMusic.class));
img_music.setBackgroundResource(R.drawable.music_off_icon);
}else {
startService(new Intent(MainActivity.this,PlayMusic.class));
img_music.setBackgroundResource(R.drawable.music_on_icon);
}
}
public void set_night(View view){
YoYo.with(Techniques.RotateIn).duration(800).playOn(img_night);
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
if (night_mode){
lin_main.setBackgroundResource(0);
img_night.setBackgroundResource(R.drawable.moon_icon);
img_main.setBackgroundResource(R.drawable.main);
sharedP.edit().putBoolean(Items.NIGHT_MODE, false).apply();
night_mode=false;
}else {
lin_main.setBackgroundResource(R.color.Black0);
img_night.setBackgroundResource(R.drawable.sun_icon);
img_main.setBackgroundResource(R.drawable.main2);
sharedP.edit().putBoolean(Items.NIGHT_MODE, true).apply();
night_mode=true;
}
}
},800);
}
@Override
protected void onResume() {
super.onResume();
get_night();
}
@Override
protected void onDestroy() {
stopService(new Intent(MainActivity.this,PlayMusic.class));
super.onDestroy();
}
public void finish(View view) {
mDrawer.closeMenu(true);
finish();
}
@SuppressLint("ResourceAsColor")
private void taptarget(){
new MaterialTapTargetPrompt.Builder(MainActivity.this)
.setTarget(R.id.img_night)
.setPrimaryText("فعال کردن حالت شب")
.setSecondaryText("با زدن این دکمه میتوانید حالت مطالعه در شب را فعال یا غیر فعال کنید")
//.setPrimaryTextColour(Color.parseColor("#13dc74"))
// .setSecondaryTextColour(Color.parseColor("#13dc74"))
.setFocalColour(R.color.mycolorGray)
.setBackButtonDismissEnabled(false)
.setBackgroundColour(Color.parseColor("#635B5B"))
.setPromptStateChangeListener(new MaterialTapTargetPrompt.PromptStateChangeListener()
{
@Override
public void onPromptStateChanged(MaterialTapTargetPrompt prompt, int state)
{
if (state == MaterialTapTargetPrompt.STATE_FOCAL_PRESSED|| state==MaterialTapTargetPrompt.STATE_NON_FOCAL_PRESSED)
{
// User has pressed the prompt target
//Toast.makeText(MainActivity.this, "اولی", Toast.LENGTH_SHORT).show();
txt_target();
}
}
})
.show();
}
private void txt_target(){
new MaterialTapTargetPrompt.Builder(MainActivity.this)
.setTarget(R.id.img_icon)
.setFocalColour(R.color.mycolorGray)
.setPrimaryText("منوی کشویی")
.setSecondaryText("با زدن این دکمه منوی کشویی برنامه باز خواهد شد که شامل آیتم های مختلفی می باشد")
.setBackgroundColour(Color.parseColor("#635B5B"))
.setPromptStateChangeListener(new MaterialTapTargetPrompt.PromptStateChangeListener()
{
@Override
public void onPromptStateChanged(MaterialTapTargetPrompt prompt, int state)
{
if (state == MaterialTapTargetPrompt.STATE_FOCAL_PRESSED || state==MaterialTapTargetPrompt.STATE_NON_FOCAL_PRESSED)
{
// User has pressed the prompt target
//Toast.makeText(MainActivity.this, "دومی", Toast.LENGTH_SHORT).show();
target3();
}
}
})
.show();
}
private void target3(){
new MaterialTapTargetPrompt.Builder(MainActivity.this)
.setTarget(R.id.img_music)
.setPrimaryText("فعال/غیرفعال موزیک")
.setSecondaryText("با زدن این دکمه میتوانید موزیک پس زمینه حین مطالعه را پخش یا قطع کنید")
.setBackgroundColour(Color.parseColor("#635B5B"))
.setPromptStateChangeListener(new MaterialTapTargetPrompt.PromptStateChangeListener()
{
@Override
public void onPromptStateChanged(MaterialTapTargetPrompt prompt, int state)
{
if (state == MaterialTapTargetPrompt.STATE_FOCAL_PRESSED || state==MaterialTapTargetPrompt.STATE_NON_FOCAL_PRESSED)
{
// User has pressed the prompt target
//Toast.makeText(MainActivity.this, "دومی", Toast.LENGTH_SHORT).show();
target4();
}
}
})
.show();
}
private void target4(){
new MaterialTapTargetPrompt.Builder(MainActivity.this)
.setTarget(R.id.img_setting)
.setPrimaryText("تنظیمات")
.setSecondaryText("با زدن این دکمه بخش تنظیمات باز خواهد شد که شامل تغییر فونت متن ، سایز متن و ... می باشد")
.setBackgroundColour(Color.parseColor("#635B5B"))
.setPromptStateChangeListener(new MaterialTapTargetPrompt.PromptStateChangeListener()
{
@Override
public void onPromptStateChanged(MaterialTapTargetPrompt prompt, int state)
{
if (state == MaterialTapTargetPrompt.STATE_FOCAL_PRESSED || state==MaterialTapTargetPrompt.STATE_NON_FOCAL_PRESSED)
{
// User has pressed the prompt target
//Toast.makeText(MainActivity.this, "دومی", Toast.LENGTH_SHORT).show();
sharedP.edit().putBoolean(Items.INTROPAGE, false).apply();
}
}
})
.show();
}
@Override
public void onBackPressed() {
if (!(exit ==null)){
super.onBackPressed();
//MainActivity.this.finish();
}else {
exit = Toast.makeText(this,"برای خروج دوباره بزنید",Toast.LENGTH_LONG);
exit.show();
}
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
exit= null;
}
},3000);
}
}
这是我的主要活动 xml 代码：
Splash Screen Activity Run enters Intro Page. After clicking the reject or complete button, the program will not enter the activity menu and the program will close.
请遵循以下选项。希望您的问题能够得到解决。
1) 您的清单必须更改，如下所示 活动名称必须指定为“.YourActivityname”
<activity
android:name=".MainActivity" >
</activity>
2）清理并重建项目并希望它能发挥作用。