java - 出现错误 java.lang.RuntimeException : Unable to start activity ComponentInfo

Question

我正在学习如何使用线性布局。我创建了一个新的布局资源文件，拖动按钮和文本，调整它们的属性。尝试在具有 API 16 的虚拟设备上运行时，该应用程序崩溃。我尝试了以下解决方案，但没有成功:

• 我已将 API 更改为 15
• 我已将应用主题更改为 Holo.light.DarkActionBar

这是日志猫:

06-14 20:56:20.692 1281-1281/? D/dalvikvm: Late-enabling CheckJNI
06-14 20:56:20.728 1281-1287/? D/dalvikvm: Debugger has detached; object registry had 1 entries
06-14 20:56:20.796 1281-1281/? W/dalvikvm: VFY: unable to find class referenced in signature (Landroid/view/SearchEvent;)
06-14 20:56:20.800 1281-1281/? I/dalvikvm: Could not find method android.view.Window$Callback.onSearchRequested, referenced from method android.support.v7.view.WindowCallbackWrapper.onSearchRequested
06-14 20:56:20.800 1281-1281/? W/dalvikvm: VFY: unable to resolve interface method 18815: Landroid/view/Window$Callback;.onSearchRequested (Landroid/view/SearchEvent;)Z
06-14 20:56:20.800 1281-1281/? D/dalvikvm: VFY: replacing opcode 0x72 at 0x0002
06-14 20:56:20.800 1281-1281/? I/dalvikvm: Could not find method android.view.Window$Callback.onWindowStartingActionMode, referenced from method android.support.v7.view.WindowCallbackWrapper.onWindowStartingActionMode
06-14 20:56:20.800 1281-1281/? W/dalvikvm: VFY: unable to resolve interface method 18819: Landroid/view/Window$Callback;.onWindowStartingActionMode (Landroid/view/ActionMode$Callback;I)Landroid/view/ActionMode;
06-14 20:56:20.800 1281-1281/? D/dalvikvm: VFY: replacing opcode 0x72 at 0x0002
06-14 20:56:20.816 1281-1281/? D/AndroidRuntime: Shutting down VM
06-14 20:56:20.816 1281-1281/? W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0xa6253288)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime: FATAL EXCEPTION: main
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.shubhendu.linearlayoutexperiments/com.example.shubhendu.linearlayoutexperiments.MainActivity}: java.lang.NullPointerException
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.app.ActivityThread.access$600(ActivityThread.java:130)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:99)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:137)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:4745)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at java.lang.reflect.Method.invokeNative(Native Method)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:511)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at dalvik.system.NativeStart.main(Native Method)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:  Caused by: java.lang.NullPointerException
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at com.example.shubhendu.linearlayoutexperiments.MainActivity.onCreate(MainActivity.java:22)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.app.Activity.performCreate(Activity.java:5008)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.app.ActivityThread.access$600(ActivityThread.java:130) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:99) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:137) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:4745) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at java.lang.reflect.Method.invokeNative(Native Method) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:511) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
06-14 20:56:20.816 1281-1281/? E/AndroidRuntime:     at dalvik.system.NativeStart.main(Native Method) 
06-14 20:56:22.640 1281-1281/? I/Process: Sending signal. PID: 1281 SIG: 9

我的MainActivity.java:

package com.example.shubhendu.linearlayoutexperiments;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.linear_experiment);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.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();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

还有我的 Linear_experiment.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_weight=".5"
        android:gravity="center_horizontal">

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="New Button"
            android:id="@+id/button" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="New Button"
            android:id="@+id/button2" />
    </LinearLayout>

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_weight="0.5">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="New Text"
            android:id="@+id/textView"
            android:layout_gravity="center_horizontal"
            android:layout_marginTop="20dp" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="New Text"
            android:id="@+id/textView2"
            android:layout_gravity="center_horizontal"
            android:layout_marginTop="20dp" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="New Text"
            android:id="@+id/textView3"
            android:layout_gravity="center_horizontal"
            android:layout_marginTop="20dp" />
    </LinearLayout>
</LinearLayout>

Answer 1

Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);

您的布局中没有任何内容是工具栏或具有android:id="@+id/toolbar"。

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);

您的布局中没有任何 FloatingActionButton 或具有 android:id="@+id/fab"。