I want to use File chooser in my app. It crashes in the part where I want to append selected text to the view, specifically when I want to form setOnClickListener for TextView. Below is the mainactivity of the app;
package de.kai_morich.simple_bluetooth_terminal;
import android.Manifest;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;
import androidx.fragment.app.FragmentManager;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import com.jjoe64.graphview.GraphView;
import com.jjoe64.graphview.series.DataPoint;
import com.jjoe64.graphview.series.LineGraphSeries;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
public class MainActivity extends AppCompatActivity implements FragmentManager.OnBackStackChangedListener {
private static final int PERMISSION_REQUEST_CODE = 100;
Button read;
TextView output;
@Override
protected void onCreate(Bundle savedInstanceState) {
read = findViewById(R.id.read);
output = findViewById(R.id.output);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
getSupportFragmentManager().addOnBackStackChangedListener(this);
if (savedInstanceState == null)
getSupportFragmentManager().beginTransaction().add(R.id.fragment, new DevicesFragment(), "devices").commit();
else
onBackStackChanged();
read.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state)) {
if (Build.VERSION.SDK_INT >= 23) {
if (checkPermission()) {
File sdcard = Environment.getExternalStorageDirectory();
File dir = new File(sdcard.getAbsolutePath() + "/text/");
if(dir.exists()) {
File file = new File(dir, "sample.txt");
FileOutputStream os = null;
StringBuilder text = new StringBuilder();
try {
BufferedReader br = new BufferedReader(new FileReader(file));
String line;
while ((line = br.readLine()) != null) {
text.append(line);
text.append('\n');
}
br.close();
} catch (IOException e) {
//You'll need to add proper error handling here
}
output.setText(text);
}
} else {
requestPermission(); // Code for permission
}
} else {
File sdcard = Environment.getExternalStorageDirectory();
File dir = new File(sdcard.getAbsolutePath() + "/text/");
if(dir.exists()) {
File file = new File(dir, "sample.txt");
FileOutputStream os = null;
StringBuilder text = new StringBuilder();
try {
BufferedReader br = new BufferedReader(new FileReader(file));
String line;
while ((line = br.readLine()) != null) {
text.append(line);
text.append('\n');
}
br.close();
} catch (IOException e) {
//You'll need to add proper error handling here
}
output.setText(text);
}
}
}
}
});
}
private boolean checkPermission() {
int result = ContextCompat.checkSelfPermission(MainActivity.this, android.Manifest.permission.READ_EXTERNAL_STORAGE);
if (result == PackageManager.PERMISSION_GRANTED) {
return true;
} else {
return false;
}
}
private void requestPermission() {
if (ActivityCompat.shouldShowRequestPermissionRationale(MainActivity.this, android.Manifest.permission.READ_EXTERNAL_STORAGE)) {
Toast.makeText(MainActivity.this, "Write External Storage permission allows us to read files. Please allow this permission in App Settings.", Toast.LENGTH_LONG).show();
} else {
ActivityCompat.requestPermissions(MainActivity.this, new String[]{android.Manifest.permission.READ_EXTERNAL_STORAGE}, PERMISSION_REQUEST_CODE);
}
}
@Override
public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
switch (requestCode) {
case PERMISSION_REQUEST_CODE:
if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
Log.e("value", "Permission Granted, Now you can use local drive .");
} else {
Log.e("value", "Permission Denied, You cannot use local drive .");
}
break;
}
}
@Override
public void onBackStackChanged() {
getSupportActionBar().setDisplayHomeAsUpEnabled(getSupportFragmentManager().getBackStackEntryCount()>0);
}
@Override
public boolean onSupportNavigateUp() {
onBackPressed();
return true;
}
}
below is the error code that I recieve, I am not sure how to fix NullPointerException error;
2020-09-15 10:41:06.244 9578-9578/de.kai_morich.simple_bluetooth_terminal E/AndroidRuntime: FATAL EXCEPTION: main
Process: de.kai_morich.simple_bluetooth_terminal, PID: 9578
java.lang.RuntimeException: Unable to start activity ComponentInfo{de.kai_morich.simple_bluetooth_terminal/de.kai_morich.simple_bluetooth_terminal.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2750)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2811)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1528)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6316)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:762)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at de.kai_morich.simple_bluetooth_terminal.MainActivity.onCreate(MainActivity.java:57)
at android.app.Activity.performCreate(Activity.java:6757)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2703)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2811)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1528)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6316)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:872)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:762)
