这是条形码扫描应用程序。当我扫描代码时，它崩溃了。如果有人知道如何解决，请帮帮我。
我从ScanActivity.java扫描代码并将对象传递到TicketResultActivity.java以显示结果后，它崩溃了。
错误
java.lang.RuntimeException：无法启动活动ComponentInfo {info.androidhive.movietickets / info.androidhive.movietickets.TicketResultActivity}：java.lang.NullPointerException：尝试调用虚拟方法'void info.androidhive.movietickets.MyApplication .addToRequestQueue（com.android.volley.Request）'上的空对象引用
MainActivity.java
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.activity_main);
// making toolbar transparent
transparentToolbar();
setContentView(R.layout.activity_main);
findViewById(R.id.btn_scan).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
startActivity(new Intent(MainActivity.this, ScanActivity.class));
}
});
}
private void transparentToolbar() {
if (Build.VERSION.SDK_INT >= 19 && Build.VERSION.SDK_INT < 21) {
setWindowFlag(this, WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS, true);
}
if (Build.VERSION.SDK_INT >= 19) {
getWindow().getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_STABLE | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
}
if (Build.VERSION.SDK_INT >= 21) {
setWindowFlag(this, WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS, false);
getWindow().setStatusBarColor(Color.TRANSPARENT);
}
}
private void setWindowFlag(Activity activity, final int bits, boolean on) {
Window win = activity.getWindow();
WindowManager.LayoutParams winParams = win.getAttributes();
if (on) {
winParams.flags |= bits;
} else {
winParams.flags &= ~bits;
}
win.setAttributes(winParams);
}
}
ScanActivity.java
public class ScanActivity extends AppCompatActivity implements BarcodeReader.BarcodeReaderListener{
BarcodeReader barcodeReader;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_scan);
// get the barcode reader instance
barcodeReader = (BarcodeReader) getSupportFragmentManager().findFragmentById(R.id.barcode_scanner);
}
@Override
public void onScanned(Barcode barcode) {
// playing barcode reader beep sound
barcodeReader.playBeep();
// ticket details activity by passing barcode
Intent intent = new Intent(ScanActivity.this, TicketResultActivity.class);
intent.putExtra("code", barcode.displayValue);
startActivity(intent);
}
@Override
public void onScannedMultiple(List<Barcode> list) {
}
@Override
public void onBitmapScanned(SparseArray<Barcode> sparseArray) {
}
/*@Override
public void onCameraPermissionDenied() {
finish();
}*/
@Override
public void onScanError(String s) {
Toast.makeText(getApplicationContext(), "Error occurred while scanning " + s, Toast.LENGTH_SHORT).show();
}
}
TicketResultActivity.java
public class TicketResultActivity extends AppCompatActivity {
private static final String TAG = TicketResultActivity.class.getSimpleName();
// url to search barcode
private static final String URL = "https://api.androidhive.info/barcodes/search.php?code=";
private TextView txtName, txtDuration, txtDirector, txtGenre, txtRating, txtPrice, txtError;
private ImageView imgPoster;
private Button btnBuy;
private ProgressBar progressBar;
private TicketView ticketView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_ticket_result);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
txtName = findViewById(R.id.name);
txtDirector = findViewById(R.id.director);
txtDuration = findViewById(R.id.duration);
txtPrice = findViewById(R.id.price);
txtRating = findViewById(R.id.rating);
imgPoster = findViewById(R.id.poster);
txtGenre = findViewById(R.id.genre);
btnBuy = findViewById(R.id.btn_buy);
imgPoster = findViewById(R.id.poster);
txtError = findViewById(R.id.txt_error);
ticketView = findViewById(R.id.layout_ticket);
progressBar = findViewById(R.id.progressBar);
String barcode = getIntent().getStringExtra("code");
// close the activity in case of empty barcode
if (TextUtils.isEmpty(barcode)) {
Toast.makeText(getApplicationContext(), "Barcode is empty!", Toast.LENGTH_LONG).show();
finish();
}
// search the barcode
searchBarcode(barcode);
}
/**
* Searches the barcode by making HTTP call
* Request was made using Volley network library but the library is
* not suggested in production, consider using Retrofit
*/
private void searchBarcode(String barcode) {
// making volley's json request
JsonObjectRequest jsonObjReq = new JsonObjectRequest(Request.Method.GET,
URL + barcode, null,
new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
Log.e(TAG, "Ticket response: " + response.toString());
// check for success status
if (!response.has("error")) {
// received movie response
renderMovie(response);
} else {
// no movie found
showNoTicket();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e(TAG, "Error: " + error.getMessage());
showNoTicket();
}
});
MyApplication.getInstance().addToRequestQueue(jsonObjReq);
}
private void showNoTicket() {
txtError.setVisibility(View.VISIBLE);
ticketView.setVisibility(View.GONE);
progressBar.setVisibility(View.GONE);
}
/**
* Rendering movie details on the ticket
*/
private void renderMovie(JSONObject response) {
try {
// converting json to movie object
Movie movie = new Gson().fromJson(response.toString(), Movie.class);
if (movie != null) {
txtName.setText(movie.getName());
txtDirector.setText(movie.getDirector());
txtDuration.setText(movie.getDuration());
txtGenre.setText(movie.getGenre());
txtRating.setText("" + movie.getRating());
txtPrice.setText(movie.getPrice());
Glide.with(this).load(movie.getPoster()).into(imgPoster);
if (movie.isReleased()) {
btnBuy.setText(getString(R.string.btn_buy_now));
btnBuy.setTextColor(ContextCompat.getColor(this, R.color.colorPrimary));
} else {
btnBuy.setText(getString(R.string.btn_coming_soon));
btnBuy.setTextColor(ContextCompat.getColor(this, R.color.btn_disabled));
}
ticketView.setVisibility(View.VISIBLE);
progressBar.setVisibility(View.GONE);
} else {
// movie not found
showNoTicket();
}
} catch (JsonSyntaxException e) {
Log.e(TAG, "JSON Exception: " + e.getMessage());
showNoTicket();
Toast.makeText(getApplicationContext(), "Error occurred. Check your LogCat for full report", Toast.LENGTH_SHORT).show();
} catch (Exception e) {
// exception
showNoTicket();
Toast.makeText(getApplicationContext(), "Error occurred. Check your LogCat for full report", Toast.LENGTH_SHORT).show();
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
if (item.getItemId() == android.R.id.home) {
finish();
}
return super.onOptionsItemSelected(item);
}
private class Movie {
String name;
String director;
String poster;
String duration;
String genre;
String price;
float rating;
@SerializedName("released")
boolean isReleased;
public String getName() {
return name;
}
public String getDirector() {
return director;
}
public String getPoster() {
return poster;
}
public String getDuration() {
return duration;
}
public String getGenre() {
return genre;
}
public String getPrice() {
return price;
}
public float getRating() {
return rating;
}
public boolean isReleased() {
return isReleased;
}
}
}
MyApplication.java
public class MyApplication extends Application {
public static final String TAG = MyApplication.class
.getSimpleName();
private RequestQueue mRequestQueue;
private static MyApplication mInstance;
@Override
public void onCreate() {
super.onCreate();
mInstance = this;
}
public static synchronized MyApplication getInstance() {
return mInstance;
}
public RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
mRequestQueue = Volley.newRequestQueue(getApplicationContext());
}
return mRequestQueue;
}
public <T> void addToRequestQueue(Request<T> req, String tag) {
// set the default tag if tag is empty
req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
getRequestQueue().add(req);
}
public <T> void addToRequestQueue(Request<T> req) {
req.setTag(TAG);
getRequestQueue().add(req);
}
public void cancelPendingRequests(Object tag) {
if (mRequestQueue != null) {
mRequestQueue.cancelAll(tag);
}
}
}
答案 0 :(得分：1)
要正确初始化MyApplication，您必须在AndroidManifest.xml
<application android:name="com.package.subpackage.MyApplication">
...
</application>