android 中的配置更改时如何解决 edittext 中的 getLayout() 方法变为 null 时的问题

Question

我正在尝试使用 textwatcher 界面从其 addTextChangeListener 中的多行 Edittext 获取单行。

我想用这个 EditText 的唯一第一行更新另一个 EditText。一切正常，除了旋转设备时，activity 和整个应用程序终止

public class CreateNoteActivity extends AppCompatActivity {

private EditText etNote, etNoteTitle;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_create_note);
    setTitle("Write Note");

    etNoteTitle = findViewById(R.id.etNoteTitle);
    etNote = findViewById(R.id.etNote);
    etNote.requestFocus();

    etNote.addTextChangedListener(new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {

        }

        @Override
        public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
            int start = etNote.getLayout().getLineStart(0);
            int end = etNote.getLayout().getLineEnd(0);
            String title = etNote.getText().subSequence(start, end).toString();
            etNoteTitle.setText(title);




        }

        @Override
        public void afterTextChanged(Editable editable) {

        }
    });
}

}

但是当旋转屏幕时发生配置更改时，会出现以下错误，是否有任何其他方法可以从多行 Edittext 中获取单行文本，如果可以的话，将不胜感激，提前谢谢

1-21 16:47:28.792 12534-12534/com.example.haadee.noteitdown E/AndroidRuntime: FATAL EXCEPTION: main
                                                                           Process: com.example.haadee.noteitdown, PID: 12534
                                                                           java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.haadee.noteitdown/com.example.haadee.noteitdown.ui.CreateNoteActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.text.Layout.getLineStart(int)' on a null object reference
                                                                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2678)
                                                                               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2743)
                                                                               at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4560)
                                                                               at android.app.ActivityThread.-wrap19(ActivityThread.java)
                                                                               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1496)
                                                                               at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                               at android.os.Looper.loop(Looper.java:154)
                                                                               at android.app.ActivityThread.main(ActivityThread.java:6165)
                                                                               at java.lang.reflect.Method.invoke(Native Method)
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)
                                                                            Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int android.text.Layout.getLineStart(int)' on a null object reference
                                                                               at com.example.haadee.noteitdown.ui.CreateNoteActivity.onTextChanged(CreateNoteActivity.java:39)
                                                                               at android.widget.TextView.sendOnTextChanged(TextView.java:8231)
                                                                               at android.widget.TextView.setText(TextView.java:4512)
                                                                               at android.widget.TextView.setText(TextView.java:4366)
                                                                               at android.widget.EditText.setText(EditText.java:89)
                                                                               at android.widget.TextView.setText(TextView.java:4341)
                                                                               at android.widget.TextView.onRestoreInstanceState(TextView.java:4232)
                                                                               at android.view.View.dispatchRestoreInstanceState(View.java:15767)
                                                                               at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3240)
                                                                               at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3240)
                                                                               at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3240)
                                                                               at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3240)
                                                                               at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:3240)
                                                                               at android.view.View.restoreHierarchyState(View.java:15745)
                                                                               at com.android.internal.policy.PhoneWindow.restoreHierarchyState(PhoneWindow.java:2106)
                                                                               at android.app.Activity.onRestoreInstanceState(Activity.java:1051)
                                                                               at android.app.Activity.performRestoreInstanceState(Activity.java:1006)
                                                                               at android.app.Instrumentation.callActivityOnRestoreInstanceState(Instrumentation.java:1196)
                                                                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2651)
                                                                               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2743) 
                                                                               at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4560) 
                                                                               at android.app.ActivityThread.-wrap19(ActivityThread.java) 
                                                                               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1496) 
                                                                               at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                               at android.os.Looper.loop(Looper.java:154) 
                                                                               at android.app.ActivityThread.main(ActivityThread.java:6165) 
                                                                               at java.lang.reflect.Method.invoke(Native Method) 
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888) 
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778) 

Answer 1

EditText getLayout() 方法在设备旋转时可以为空。 如此安全的方法首先进行空检查。

更新方法为：

@Override
    public void onTextChanged(CharSequence s, int i, int before, int count) {
        // do null check here
        if (etNote.getLayout() != null) {
            int start = etNote.getLayout().getLineStart(0);
            int end = etNote.getLayout().getLineEnd(0);
            String title = etNote.getText().subSequence(start, end).toString();
            etNoteTitle.setText(title);
        }

    }