Android-LayoutParams的那些事

原文：http://tryenough.com/android-layoutparams

LayoutParams是什麼？

LayoutParams是View用來告訴它的父控件如何放置本身的，LayoutParams是ViewGroup類裏的一個靜態內部類。

ViewGroup.LayoutParams僅僅描述了這個View想要的寬度和高度。能夠理解成LayoutParams是子View告訴父View自身寬高的橋樑。

可取的值：

• fill_parent 強制性使子視圖的大小擴展至與父視圖大小相等（不含 padding )
• match_parent 與fill_parent相同，用於Android 2.3 & 以後版本
• wrap_content 自適應大小，強制性地使視圖擴展以便顯示其所有內容(含 padding )

不一樣ViewGroup的繼承類對應着不一樣的ViewGroup.LayoutParams的子類，例如：ViewGroup.MarginLayoutParams, WindowManager.LayoutParams等。

原文：http://tryenough.com/android-layoutparams

實際使用的一個例子

Activity:

public class MoveActivity extends AppCompatActivity {
    private ImageView mIv;
    private TextView mTvBlue;
    private TextView mTvGreen;
    private ViewGroup.LayoutParams mVgLp;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_move);
        mIv = (ImageView) findViewById(R.id.mIv);
        mTvBlue = (TextView) findViewById(R.id.mTvBlue);
        mTvGreen = (TextView) findViewById(R.id.mTvGreen);

        mVgLp = mIv.getLayoutParams();

        findViewById(R.id.mTvMoveRight).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                ViewGroup.LayoutParams vg_lp = mIv.getLayoutParams();
                // RelativeLayout.LayoutParams 不可抽取爲成員變量
                RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(vg_lp);
                params.addRule(RelativeLayout.ALIGN_PARENT_RIGHT, R.id.mIv);
                mIv.setLayoutParams(params); //使layout更新
            }
        });

        findViewById(R.id.mTvMoveLeft).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // 左 （默認處於頂部，因此看起來是左上）
                RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(mVgLp);
                params.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
                mIv.setLayoutParams(params);
            }
        });

        findViewById(R.id.mTvCenter).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // 居中
                RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(mVgLp);
                params.addRule(RelativeLayout.CENTER_IN_PARENT);
                mIv.setLayoutParams(params);
            }
        });

        findViewById(R.id.mTvLeftVer).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // 左部垂直居中
                RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(mVgLp);
                params.addRule(RelativeLayout.ALIGN_PARENT_LEFT|RelativeLayout.CENTER_VERTICAL);
                mIv.setLayoutParams(params);
            }
        });

        findViewById(R.id.mTvRightBot).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // 右下
                RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(mVgLp);
                params.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM);
                params.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
                mIv.setLayoutParams(params);
            }
        });
        // 綠在藍右邊
        findViewById(R.id.mTvaGRightB).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                ViewGroup.LayoutParams vgLp = mTvGreen.getLayoutParams();
                RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(vgLp);
                params.addRule(RelativeLayout.RIGHT_OF,R.id.mTvBlue);
                mTvGreen.setLayoutParams(params);
            }
        });

        // 綠在藍下邊
        findViewById(R.id.mTvGElowB).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                ViewGroup.LayoutParams vgLp = mTvGreen.getLayoutParams();
                RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(vgLp);
                params.addRule(RelativeLayout.BELOW,R.id.mTvBlue);
                mTvGreen.setLayoutParams(params);
            }
        });
    }
}
複製代碼

佈局xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:id="@+id/activity_main" 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" android:orientation="vertical" tools:context="com.amqr.movetest.MoveActivity">
    <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal" >
        <TextView android:id="@+id/mTvMoveLeft" android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="#6600ff00" android:padding="10dp" android:layout_margin="10dp" android:text="黑色最左！！"/>
        <TextView android:id="@+id/mTvMoveRight" android:layout_width="wrap_content" android:layout_height="wrap_content" android:padding="10dp" android:background="#6600ff00" android:layout_margin="10dp" android:text="黑色最右！！"/>
        <TextView android:id="@+id/mTvCenter" android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="#6600ff00" android:padding="10dp" android:layout_margin="10dp" android:text="黑色居中"/>
    </LinearLayout>
    <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal" >
        <TextView android:id="@+id/mTvLeftVer" android:layout_width="wrap_content" android:layout_height="wrap_content" android:padding="10dp" android:background="#6600ff00" android:layout_margin="10dp" android:text="黑色靠左垂直居中"/>
        <TextView android:id="@+id/mTvRightBot" android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="#6600ff00" android:padding="10dp" android:layout_margin="10dp" android:text="黑色右下角"/>
    </LinearLayout>
    <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal" >
        <TextView android:id="@+id/mTvaGRightB" android:layout_width="wrap_content" android:layout_height="wrap_content" android:padding="10dp" android:background="#6600ff00" android:layout_margin="10dp" android:text="綠在藍右邊"/>
        <TextView android:id="@+id/mTvGElowB" android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="#6600ff00" android:padding="10dp" android:layout_margin="10dp" android:text="綠在藍下邊"/>
    </LinearLayout>
    <RelativeLayout android:layout_width="match_parent" android:layout_height="200px" android:background="#66ff0000" >
        <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="RelativeLayout" android:layout_centerInParent="true" />
        <ImageView android:id="@+id/mIv" android:layout_width="30dp" android:layout_height="40px" android:background="#000" android:layout_centerHorizontal="true" />
        <TextView android:id="@+id/mTvBlue" android:layout_width="20dp" android:layout_height="20dp" android:text="藍" android:gravity="center" android:background="#660000ff" />
        <TextView android:id="@+id/mTvGreen" android:layout_width="20dp" android:layout_height="20dp" android:text="綠" android:gravity="center" android:background="#6600ff00" android:layout_below="@id/mTvBlue" />
    </RelativeLayout>
</LinearLayout>
複製代碼