textView setText（）NullPointerException [英] textView setText() NullPointerException

问题描述

我有一个几乎完全香草的应用程序。我要做的就是更改textView的文本，但它给了我一个NullPointerException。我没有XML配置，没有添加方法，没什么特别的。我检查了我的类，它指向了正确的XML，并且XML中确实有一个带有正确id的textView元素。

I have an almost completely Vanilla App. All I'm trying to do is change the text of a textView, but it gives me a NullPointerException. I have no XML configuration, no added methods, nothing special. I checked my class, and it's pointing to the correct XML, and the XML does have a textView element in it with the correct id.

我也尝试过创建textView在类级别上的onCreate（）之外的实例，无论如何，应用程序都无法启动。我敢肯定我很容易忽视，但我找不到答案。谢谢您的帮助。
编辑：
我意识到我需要移动这段代码才能访问片段资源，但是当我这样做时，它会给我一个错误：

I have also tried creating the textView instance outside of onCreate() on the class level, and the app just fails to start no matter what. I'm sure I'm overlooking simple, but I can't find the answer. Thanks for the help. I realize that I need to move this code so that it accesses fragment resources, but when I do, it gives me an error:

无法对类型为Activity的非静态方法findViewById（int）进行静态引用

Cannot make a static reference to the non-static method findViewById(int) from the type Activity

如果我的所有视图都在我的视图中，我应该在哪里放置代码片段，而不是我的Activity XML？或者我应该让活动加载片段开始？
package com.example.testapp;

Where should I put my code if ALL of my views are in my fragment, and not in my Activity XML? or should I just have the activity load the fragment to begin with? package com.example.testapp;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.os.Build;

public class MainActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView tv = (TextView) findViewById(R.id.textView1);
        tv.setText("Teststring");

    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
        .add(R.id.container, new PlaceholderFragment()).commit();
    }


    }



    @Override
    public boolean onCreateOptionsMenu(Menu menu) {


        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;


    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }


    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container,
                    false);
            return rootView;
        }

    }


}

错误日志：

06-14 17:02:27.405: E/AndroidRuntime(1420): FATAL EXCEPTION: main
06-14 17:02:27.405: E/AndroidRuntime(1420): Process: com.example.testapp, PID: 1420
06-14 17:02:27.405: E/AndroidRuntime(1420): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.testapp/com.example.testapp.MainActivity}: java.lang.NullPointerException
06-14 17:02:27.405: E/AndroidRuntime(1420):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at android.os.Handler.dispatchMessage(Handler.java:102)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at android.os.Looper.loop(Looper.java:136)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at android.app.ActivityThread.main(ActivityThread.java:5017)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at java.lang.reflect.Method.invokeNative(Native Method)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at java.lang.reflect.Method.invoke(Method.java:515)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at dalvik.system.NativeStart.main(Native Method)
06-14 17:02:27.405: E/AndroidRuntime(1420): Caused by: java.lang.NullPointerException
06-14 17:02:27.405: E/AndroidRuntime(1420):     at com.example.testapp.MainActivity.onCreate(MainActivity.java:23)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at android.app.Activity.performCreate(Activity.java:5231)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
06-14 17:02:27.405: E/AndroidRuntime(1420):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
06-14 17:02:27.405: E/AndroidRuntime(1420):     ... 11 more

XML fragment_main

XML fragment_main

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.testapp.MainActivity$PlaceholderFragment" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

</RelativeLayout>

推荐答案

你能发布xml吗？你的java假设R.id.textView1的id可能是错误的。也许R.id.textview1？

Can you post xml? It's likely that the id your java is assuming "R.id.textView1" is wrong. Maybe R.id.textview1?

如果您的文本视图位于片段内部，请执行以下操作：

Well if your text view lives inside the fragment just do this:

@Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container,
                    false);
            TextView tv = (TextView) rootView.findViewById(R.id.textView1);
        tv.setText("Teststring");
            return rootView;
        }

这篇关于textView setText（）NullPointerException的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！