Android '；应用程序不断停止'；通过添加RelativeLayout.LayoutParams

我对安卓系统还很陌生，我正在关注Newboston的教程系列

目前正在观看视频34：动画和过渡

本视频的目标是将按钮从左上设置为右下。

以下是MainActivity类的代码：

package com.example.jarno.a34_animations;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.transition.TransitionManager;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.RelativeLayout;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "debugMessage";

    ViewGroup mainLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.i(TAG, "set activity_main");

        mainLayout = (ViewGroup) findViewById(R.id.mainLayout);

        // Click screen
        mainLayout.setOnTouchListener(
                new RelativeLayout.OnTouchListener() {
                    @Override
                    public boolean onTouch(View v, MotionEvent event) {
                        moveButton();
                        Log.i(TAG, "button click");
                        return true;
                    }
                }
        );
    }

    public void moveButton() {
        View animationButton = findViewById(R.id.animationButton);

        // Smooth transition
        TransitionManager.beginDelayedTransition(mainLayout);

        // Change position
        RelativeLayout.LayoutParams positionRules = new RelativeLayout.LayoutParams(
                RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
        positionRules.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM, RelativeLayout.TRUE);
        positionRules.addRule(RelativeLayout.ALIGN_PARENT_RIGHT, RelativeLayout.TRUE);
        mainLayout.setLayoutParams(positionRules);

        // Change size
        ViewGroup.LayoutParams sizeRules = animationButton.getLayoutParams();
        sizeRules.width = 450;
        sizeRules.height = 300;
        animationButton.setLayoutParams(sizeRules);
    }
}

活动\u Main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/mainLayout"
    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.jarno.a34_animations.MainActivity">

    <Button
        android:text="Button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_alignParentStart="true"
        android:id="@+id/animationButton" />
</RelativeLayout>

---

LayoutParams

a

View

的类型由其父级决定。您的

animationButton

将具有

RelativeLayout.LayoutParams

，因为它位于

RelativeLayout

中。但是，您的

mainLayout

不会，因为它实际上位于

FrameLayout

中。您可能是由于

ClassCastException

导致崩溃，因为您试图在

mainLayout

上设置错误的

LayoutParams

。视图的

LayoutParams

类型由其父级决定。您的

animationButton

将具有

RelativeLayout.LayoutParams

，因为它位于

RelativeLayout

中。但是，您的

mainLayout

不会，因为它实际上位于

FrameLayout

中。您可能由于

ClassCastException

而崩溃，因为您试图在

mainloayout

上设置错误类型的

LayoutParams

。

// Change position
        RelativeLayout.LayoutParams positionRules = new RelativeLayout.LayoutParams(
                RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
        positionRules.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM, RelativeLayout.TRUE);
        positionRules.addRule(RelativeLayout.ALIGN_PARENT_RIGHT, RelativeLayout.TRUE);
        mainLayout.setLayoutParams(positionRules);