无法使用空指针异常错误的 Butterknife

Question

我正在尝试在我的 Android 项目中使用 ButterKnife。

我有一个 Activity 实现了 Interface。我正在使用 MVP 模式。我正在尝试从 EditText 获取文本，但它抛出一个

null pointer exception.

这是我的简单代码。

Gradle 依赖项

compile 'com.jakewharton:butterknife:8.8.1'

布局

 <?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.rao.myapplication.LoginActivity">

    <EditText
        android:id="@+id/etUseName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <EditText
        android:id="@+id/etPassword"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toBottomOf="@+id/etUseName"/>
    <Button
        android:id="@+id/btnLogin"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Login"
        android:onClick="loginClick"
        app:layout_constraintTop_toBottomOf="@+id/etPassword"/>

</android.support.constraint.ConstraintLayout>

Activity

 package com.example.rao.myapplication;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.example.rao.myapplication.Presenter.LoginActivityPresenter;
import com.example.rao.myapplication.View.LoginActivityView;

import butterknife.BindView;
import butterknife.ButterKnife;

public class LoginActivity extends AppCompatActivity implements LoginActivityView {

    @BindView(R.id.etUseName)
    EditText userNameET;

    @BindView(R.id.etPassword)
    EditText passwordET;

    @BindView(R.id.btnLogin)
    Button loginBtn;

    private LoginActivityPresenter presenter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);

        ButterKnife.bind(this);
        passwordET.setText("abcd"); // Fails here as well
        presenter = new LoginActivityPresenter(this);
    }

    @Override
    public void navigateToListActivity() {

    }

    @Override
    public void loginFailed() {

    }

    public void loginClick(View view) {
        Toast.makeText(this, userNameET.getText().toString(), Toast.LENGTH_SHORT ).show(); // Fails here
        Toast.makeText(this, "test", Toast.LENGTH_SHORT ).show();
    }
}

这是错误日志

FATAL EXCEPTION: main Process: com.example.rao.myapplication, PID: 24847 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.rao.myapplication/com.example.rao.myapplication.LoginActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.EditText.setText(java.lang.CharSequence)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2927) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2988) at android.app.ActivityThread.-wrap14(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1631) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6682) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.EditText.setText(java.lang.CharSequence)' on a null object reference at com.example.rao.myapplication.LoginActivity.onCreate(LoginActivity.java:34) at android.app.Activity.performCreate(Activity.java:6942) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2880) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2988) at android.app.ActivityThread.-wrap14(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1631) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6682) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)

请你在这方面指导我正确的方向。

Answer 1

也在您的 gradle 文件中添加以下行....

compile 'com.jakewharton:butterknife:8.8.1'
annotationProcessor 'com.jakewharton:butterknife-compiler:8.+'//add this line also

希望能解决您的问题....

Answer 2

将其放入 gradle 文件并检查。这是 official documentation.

的 link

GRADLE

compile 'com.jakewharton:butterknife:8.8.1'
annotationProcessor 'com.jakewharton:butterknife-compiler:8.8.1'

Answer 3

如果你忘记在setContentView后面添加ButterKnife.bind(this);，你会得到NullPointerException。

无法使用空指针异常错误的 Butterknife

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