java - 如何在Android中正确使用snackbar

Question

我为 Android 创建了一个简单的计数器应用程序。我刚刚开始使用支持库，只是为了对其进行测试，我想显示一个 snackbar，其中显示 Hello。这是我在 MainActivity.java 文件中的代码:

package com.mapsup.counter;

import android.app.Activity;
import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import com.google.android.material.snackbar.Snackbar;

public class MainActivity extends Activity {
    long count=0;
    TextView tv;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_layout);
        SharedPreferences sp=getApplicationContext().getSharedPreferences("preferences",Context.MODE_PRIVATE);
        count=sp.getLong("count",0);
        tv=findViewById(R.id.counter);
        tv.setText(String.valueOf(count));

        //Create and display a snackbar
        Snackbar snackbar = Snackbar.make(tv,"Hello",Snackbar.LENGTH_LONG);
        snackbar.show();
    }

    public void increase(View view) {
        ++count;
        tv.setText(String.valueOf(count));
    }

    public void decrease(View view) {
        if(count>0) {
            --count;
            tv.setText(String.valueOf(count));
        }
    }

    public void reset(View view) {
        count=0;
        tv.setText("0");
    }

    @Override
    public void onStop() {
        super.onStop();
        Context ctx=getApplicationContext();
        SharedPreferences sp=ctx.getSharedPreferences("preferences",Context.MODE_PRIVATE);
        SharedPreferences.Editor editor=sp.edit();
        editor.putLong("count",count);
        editor.apply();
    }
}

这是布局 main_layout.xml 文件:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#0031A0"
    android:orientation="vertical"
    android:padding="20dp"
    android:id="@+id/root">

    <TextView
        android:id="@+id/counter"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_marginBottom="20dp"
        android:layout_weight="1"
        android:background="#B2FFFFFF"
        android:gravity="center"
        android:textSize="36sp" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="increase"
            android:text="@string/add"
            android:textSize="30sp" />

        <Button
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="decrease"
            android:text="@string/subt"
            android:textSize="30sp" />
    </LinearLayout>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="reset"
        android:text="@string/reset"
        android:textAllCaps="false"
        android:textSize="30sp" />
</LinearLayout>

当我运行应用程序时，应用程序崩溃了。 logcat 将其显示为错误消息:

2020-02-03 00:20:10.015 12849-12849/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.mapsup.counter, PID: 12849
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mapsup.counter/com.mapsup.counter.MainActivity}: android.view.InflateException: Binary XML file line #26: Binary XML file line #26: Error inflating class <unknown>
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2724)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2789)
        at android.app.ActivityThread.-wrap12(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1527)
        at android.os.Handler.dispatchMessage(Handler.java:110)
        at android.os.Looper.loop(Looper.java:203)
        at android.app.ActivityThread.main(ActivityThread.java:6251)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924)
     Caused by: android.view.InflateException: Binary XML file line #26: Binary XML file line #26: Error inflating class <unknown>
     Caused by: android.view.InflateException: Binary XML file line #26: Error inflating class <unknown>
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Constructor.newInstance0(Native Method)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:430)
        at android.view.LayoutInflater.createView(LayoutInflater.java:645)
        at com.android.internal.policy.PhoneLayoutInflater.onCreateView(PhoneLayoutInflater.java:58)
        at android.view.LayoutInflater.onCreateView(LayoutInflater.java:717)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:785)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:727)
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:858)
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:821)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:518)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:426)
        at com.google.android.material.snackbar.Snackbar.make(Snackbar.java:164)
        at com.mapsup.counter.MainActivity.onCreate(MainActivity.java:23)
        at android.app.Activity.performCreate(Activity.java:6712)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2677)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2789)
        at android.app.ActivityThread.-wrap12(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1527)
        at android.os.Handler.dispatchMessage(Handler.java:110)
        at android.os.Looper.loop(Looper.java:203)
        at android.app.ActivityThread.main(ActivityThread.java:6251)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924)
     Caused by: java.lang.UnsupportedOperationException: Failed to resolve attribute at index 6: TypedValue{t=0x2/d=0x101009b a=1}
        at android.content.res.TypedArray.getColorStateList(TypedArray.java:531)
        at android.widget.TextView.<init>(TextView.java:805)
        at android.widget.TextView.<init>(TextView.java:727)
        at android.widget.TextView.<init>(TextView.java:723)
        at java.lang.reflect.Constructor.newInstance0(Native Method) 
        at java.lang.reflect.Constructor.newInstance(Constructor.java:430) 
        at android.view.LayoutInflater.createView(LayoutInflater.java:645) 
        at com.android.internal.policy.PhoneLayoutInflater.onCreateView(PhoneLayoutInflater.java:58) 
        at android.view.LayoutInflater.onCreateView(LayoutInflater.java:717) 
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:785) 
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:727) 
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:858) 
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:821) 
        at android.view.LayoutInflater.inflate(LayoutInflater.java:518) 
        at android.view.LayoutInflater.inflate(LayoutInflater.java:426) 
        at com.google.android.material.snackbar.Snackbar.make(Snackbar.java:164) 
        at com.mapsup.counter.MainActivity.onCreate(MainActivity.java:23) 
        at android.app.Activity.performCreate(Activity.java:6712) 
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118) 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2677) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2789) 
        at android.app.ActivityThread.-wrap12(ActivityThread.java) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1527) 
        at android.os.Handler.dispatchMessage(Handler.java:110) 
        at android.os.Looper.loop(Looper.java:203) 
        at android.app.ActivityThread.main(ActivityThread.java:6251) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924) 

如果我删除 snackbar 代码，应用程序运行一切正常。根据我的想法，创建一个 Snackbar 和创建一个 Toast 是一样的，我们只需要将 Toast 替换为 Snackbar 即可。这是正确的吗？

我的错误是什么以及如何正确使用 snackbar ？

Answer 1

请将 Snackbar.make(llRootLayout,"Hello",Snackbar.LENGTH_LONG); 中的 tv 替换为 rootLayout；如下。

 public class MainActivity extends Activity {
    long count=0;
    TextView tv;|
LinearLayout llRootLayout;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_layout);
        SharedPreferences sp=getApplicationContext().getSharedPreferences("preferences",Context.MODE_PRIVATE);
        count=sp.getLong("count",0);
        tv=findViewById(R.id.counter);
llRootLayout=findViewById(R.id.root);
        tv.setText(String.valueOf(count));

        //Create and display a snackbar
       Snackbar snackbar=Snackbar.make(llRootLayout,"Hello",Snackbar.LENGTH_LONG);
        snackbar.show();
    }

    public void increase(View view) {
        ++count;
        tv.setText(String.valueOf(count));
    }

    public void decrease(View view) {
        if(count>0) {
            --count;
            tv.setText(String.valueOf(count));
        }
    }

    public void reset(View view) {
        count=0;
        tv.setText("0");
    }

    @Override
    public void onStop() {
        super.onStop();
        Context ctx=getApplicationContext();
        SharedPreferences sp=ctx.getSharedPreferences("preferences",Context.MODE_PRIVATE);
        SharedPreferences.Editor editor=sp.edit();
        editor.putLong("count",count);
        editor.apply();
    }
}