Question

我收到here

的提示

似乎有些人使用了相同的方法，没有人遇到崩溃。我有这样的java文件：

package com.example.instantinput;

import android.app.Activity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends Activity {
    private EditText m_et;
    private TextView m_tv;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        m_tv = (TextView) findViewById(R.id.tv);
        m_et = (EditText) findViewById(R.id.et);
        m_et.setHint("please enter name");
        m_et.addTextChangedListener(new TextWatcher() {
            public void afterTextChanged(Editable s) {

                m_tv.setText(m_et.getText().toString());

            }

            public void beforeTextChanged(CharSequence s, int start, int count,
                    int after) {
            }

            public void onTextChanged(CharSequence s, int start, int before,
                    int count) {

            }
        });
    }
}

但它在运行时崩溃并提供

E/AndroidRuntime(6015): java.lang.NullPointerException

在我输入第二封信之后。有人说setText中的afterTextChanged会给出无休止的迭代，所以如果希望它可以阻止这种无穷无尽的话，我会放一个。不知道接下来该做什么。谢谢。 activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
   <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        >
    <EditText
        android:id="@+id/et" 
        android:inputType="text"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        />
    <TextView        
        android:text="@+id/tv"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"        
        />
</LinearLayout>

我刚注意到textview的地方是“假”？

enter image description here

error from logcat right after the first input (of edittext):
06-04 09:04:51.249: E/AndroidRuntime(10410): FATAL EXCEPTION: main
06-04 09:04:51.249: E/AndroidRuntime(10410): java.lang.NullPointerException
06-04 09:04:51.249: E/AndroidRuntime(10410):    at com.example.instantinput.MainActivity$1.afterTextChanged(MainActivity.java:26)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.widget.TextView.sendAfterTextChanged(TextView.java:6568)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.widget.TextView$ChangeWatcher.afterTextChanged(TextView.java:6757)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.text.SpannableStringBuilder.sendTextHasChanged(SpannableStringBuilder.java:897)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.text.SpannableStringBuilder.change(SpannableStringBuilder.java:353)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.text.SpannableStringBuilder.change(SpannableStringBuilder.java:269)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:432)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:409)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:28)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.view.inputmethod.BaseInputConnection.replaceText(BaseInputConnection.java:654)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.view.inputmethod.BaseInputConnection.setComposingText(BaseInputConnection.java:415)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at com.android.internal.view.IInputConnectionWrapper.executeMessage(IInputConnectionWrapper.java:328)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at com.android.internal.view.IInputConnectionWrapper$MyHandler.handleMessage(IInputConnectionWrapper.java:79)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.os.Handler.dispatchMessage(Handler.java:99)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.os.Looper.loop(Looper.java:123)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at android.app.ActivityThread.main(ActivityThread.java:3687)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at java.lang.reflect.Method.invokeNative(Native Method)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at java.lang.reflect.Method.invoke(Method.java:507)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
06-04 09:04:51.249: E/AndroidRuntime(10410):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

看起来你的崩溃就在这条线上：

m_tv.setText(m_et.getText().toString());

必须是m_tv null。（m_et是附加了TextWatcher的视图，因此在第二个按键上不能是null。）

因此，请检查您的activity_main.xml布局文件，以确保正确定义了R.id.tv视图。如果它在那里，请做一个干净的项目构建，以防有些东西正在收集过时的数据。

使用EditText和TextView即时显示文本会导致崩溃

1 个答案: