when I call addTextChangedListener() method for editText and I implement TextWatcher class and override 3 methods beforTextChanged() onTextChanged() afterTextChanged(). the program does not give any errors but the program fails whit the implementation of the TextWatcher class and when run the app this message is displayed: "unfortunately, My Application1 has stopped"
this is code:
package com.example.myapplication1;
import androidx.appcompat.app.AppCompatActivity;
import android.annotation.SuppressLint;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Switch;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity implements View.OnClickListener, TextWatcher {
private static final String TAG= "MainActivity";
Button btn1, btn2;
ImageView imageView;
EditText editText;
CheckBox checkBox;
Switch aSwitch;
@SuppressLint("ResourceAsColor")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn1=findViewById(R.id.firstButton);
btn2=findViewById(R.id.secondButton);
imageView=findViewById(R.id.imageView);
editText.findViewById(R.id.editText);
checkBox.findViewById(R.id.checkBox);
aSwitch.findViewById(R.id.swiClick);
btn1.setText(R.string.btn);
btn1.setTextColor(getResources().getColor(R.color.purple_700));
btn1.setBackgroundColor(getResources().getColor(R.color.teal_700));
btn1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Log.d(TAG, "click btn1");
}
});
btn2.setOnClickListener(this);
imageView.setScaleType(ImageView.ScaleType.FIT_START);
Toast.makeText(this,"salam",Toast.LENGTH_SHORT).show();
editText.addTextChangedListener(this);
}
@Override
public void onClick(View v) {
Log.d(TAG, "click btn2");
}
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
Toast.makeText(this, editText.getText(),Toast.LENGTH_SHORT).show();
}
@Override
public void afterTextChanged(Editable editable) {
}
}
in run part show these message:
Install successfully finished in 1 s 492 ms.
$ adb shell am start -n "com.example.myapplication1/com.example.myapplication1.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
Connected to process 1833 on device '-google_nexus_5-192.168.81.101:5555'.
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
E/libprocessgroup: failed to make and chown /acct/uid_10060: Read-only file system
W/Zygote: createProcessGroup failed, kernel missing CONFIG_CGROUP_CPUACCT?
I/art: Late-enabling -Xcheck:jni
W/System: ClassLoader referenced unknown path: /data/app/com.example.myapplication1-1/lib/x86
W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter androidx.vectordrawable.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication1, PID: 1833
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplication1/com.example.myapplication1.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.widget.EditText.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.widget.EditText.findViewById(int)' on a null object reference
at com.example.myapplication1.MainActivity.onCreate(MainActivity.java:36)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
I/Process: Sending signal. PID: 1833 SIG: 9
wheres problem?
